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DASH(1)                BSD General Commands Manual               DASH(1)

NAME         top

     dash — command interpreter (shell)

SYNOPSIS         top

     dash [-aCefnuvxIimqVEb] [+aCefnuvxIimqVEb] [-o option_name]
          [+o option_name] [command_file [argument ...]]
     dash -c [-aCefnuvxIimqVEb] [+aCefnuvxIimqVEb] [-o option_name]
          [+o option_name] command_string [command_name [argument ...]]
     dash -s [-aCefnuvxIimqVEb] [+aCefnuvxIimqVEb] [-o option_name]
          [+o option_name] [argument ...]

DESCRIPTION         top

     dash is the standard command interpreter for the system.  The
     current version of dash is in the process of being changed to
     conform with the POSIX 1003.2 and 1003.2a specifications for the
     shell.  This version has many features which make it appear similar
     in some respects to the Korn shell, but it is not a Korn shell
     clone (see ksh(1)).  Only features designated by POSIX, plus a few
     Berkeley extensions, are being incorporated into this shell.  This
     man page is not intended to be a tutorial or a complete
     specification of the shell.

   Overview
     The shell is a command that reads lines from either a file or the
     terminal, interprets them, and generally executes other commands.
     It is the program that is running when a user logs into the system
     (although a user can select a different shell with the chsh(1)
     command).  The shell implements a language that has flow control
     constructs, a macro facility that provides a variety of features in
     addition to data storage, along with built in history and line
     editing capabilities.  It incorporates many features to aid
     interactive use and has the advantage that the interpretative
     language is common to both interactive and non-interactive use
     (shell scripts).  That is, commands can be typed directly to the
     running shell or can be put into a file and the file can be
     executed directly by the shell.

   Invocation
     If no args are present and if the standard input of the shell is
     connected to a terminal (or if the -i flag is set), and the -c
     option is not present, the shell is considered an interactive
     shell.  An interactive shell generally prompts before each command
     and handles programming and command errors differently (as
     described below).  When first starting, the shell inspects argument
     0, and if it begins with a dash ‘-’, the shell is also considered a
     login shell.  This is normally done automatically by the system
     when the user first logs in.  A login shell first reads commands
     from the files /etc/profile and .profile if they exist.  If the
     environment variable ENV is set on entry to an interactive shell,
     or is set in the .profile of a login shell, the shell next reads
     commands from the file named in ENV.  Therefore, a user should
     place commands that are to be executed only at login time in the
     .profile file, and commands that are executed for every interactive
     shell inside the ENV file.  To set the ENV variable to some file,
     place the following line in your .profile of your home directory

           ENV=$HOME/.shinit; export ENV

     substituting for “.shinit” any filename you wish.

     If command line arguments besides the options have been specified,
     then the shell treats the first argument as the name of a file from
     which to read commands (a shell script), and the remaining
     arguments are set as the positional parameters of the shell ($1,
     $2, etc).  Otherwise, the shell reads commands from its standard
     input.

   Argument List Processing
     All of the single letter options that have a corresponding name can
     be used as an argument to the -o option.  The set -o name is
     provided next to the single letter option in the description below.
     Specifying a dash “-” turns the option on, while using a plus “+”
     disables the option.  The following options can be set from the
     command line or with the set builtin (described later).

           -a allexport     Export all variables assigned to.

           -c               Read commands from the command_string
                            operand instead of from the standard input.
                            Special parameter 0 will be set from the
                            command_name operand and the positional
                            parameters ($1, $2, etc.)  set from the
                            remaining argument operands.

           -C noclobber     Don't overwrite existing files with “>”.

           -e errexit       If not interactive, exit immediately if any
                            untested command fails.  The exit status of
                            a command is considered to be explicitly
                            tested if the command is used to control an
                            if, elif, while, or until; or if the command
                            is the left hand operand of an “&&” or “||”
                            operator.

           -f noglob        Disable pathname expansion.

           -n noexec        If not interactive, read commands but do not
                            execute them.  This is useful for checking
                            the syntax of shell scripts.

           -u nounset       Write a message to standard error when
                            attempting to expand a variable that is not
                            set, and if the shell is not interactive,
                            exit immediately.

           -v verbose       The shell writes its input to standard error
                            as it is read.  Useful for debugging.

           -x xtrace        Write each command to standard error
                            (preceded by a ‘+ ’) before it is executed.
                            Useful for debugging.

           -I ignoreeof     Ignore EOF's from input when interactive.

           -i interactive   Force the shell to behave interactively.

           -l               Make dash act as if it had been invoked as a
                            login shell.

           -m monitor       Turn on job control (set automatically when
                            interactive).

           -s stdin         Read commands from standard input (set
                            automatically if no file arguments are
                            present).  This option has no effect when
                            set after the shell has already started
                            running (i.e. with set).

           -V vi            Enable the built-in vi(1) command line
                            editor (disables -E if it has been set).

           -E emacs         Enable the built-in emacs(1) command line
                            editor (disables -V if it has been set).

           -b notify        Enable asynchronous notification of
                            background job completion.  (UNIMPLEMENTED
                            for 4.4alpha)

   Lexical Structure
     The shell reads input in terms of lines from a file and breaks it
     up into words at whitespace (blanks and tabs), and at certain
     sequences of characters that are special to the shell called
     “operators”.  There are two types of operators: control operators
     and redirection operators (their meaning is discussed later).
     Following is a list of operators:

           Control operators:
                 & && ( ) ; ;; | || <newline>

           Redirection operators:
                 < > >| << >> <& >& <<- <>

   Quoting
     Quoting is used to remove the special meaning of certain characters
     or words to the shell, such as operators, whitespace, or keywords.
     There are three types of quoting: matched single quotes, matched
     double quotes, and backslash.

   Backslash
     A backslash preserves the literal meaning of the following
     character, with the exception of ⟨newline⟩.  A backslash preceding
     a ⟨newline⟩ is treated as a line continuation.

   Single Quotes
     Enclosing characters in single quotes preserves the literal meaning
     of all the characters (except single quotes, making it impossible
     to put single-quotes in a single-quoted string).

   Double Quotes
     Enclosing characters within double quotes preserves the literal
     meaning of all characters except dollarsign ($), backquote (`), and
     backslash (\).  The backslash inside double quotes is historically
     weird, and serves to quote only the following characters:
           $ ` " \ <newline>.
     Otherwise it remains literal.

   Reserved Words
     Reserved words are words that have special meaning to the shell and
     are recognized at the beginning of a line and after a control
     operator.  The following are reserved words:

           !       elif    fi      while   case
           else    for     then    {       }
           do      done    until   if      esac

     Their meaning is discussed later.

   Aliases
     An alias is a name and corresponding value set using the alias(1)
     builtin command.  Whenever a reserved word may occur (see above),
     and after checking for reserved words, the shell checks the word to
     see if it matches an alias.  If it does, it replaces it in the
     input stream with its value.  For example, if there is an alias
     called “lf” with the value “ls -F”, then the input:

           lf foobar ⟨return⟩

     would become

           ls -F foobar ⟨return⟩

     Aliases provide a convenient way for naive users to create
     shorthands for commands without having to learn how to create
     functions with arguments.  They can also be used to create
     lexically obscure code.  This use is discouraged.

   Commands
     The shell interprets the words it reads according to a language,
     the specification of which is outside the scope of this man page
     (refer to the BNF in the POSIX 1003.2 document).  Essentially
     though, a line is read and if the first word of the line (or after
     a control operator) is not a reserved word, then the shell has
     recognized a simple command.  Otherwise, a complex command or some
     other special construct may have been recognized.

   Simple Commands
     If a simple command has been recognized, the shell performs the
     following actions:

           1.   Leading words of the form “name=value” are stripped off
                and assigned to the environment of the simple command.
                Redirection operators and their arguments (as described
                below) are stripped off and saved for processing.

           2.   The remaining words are expanded as described in the
                section called “Expansions”, and the first remaining
                word is considered the command name and the command is
                located.  The remaining words are considered the
                arguments of the command.  If no command name resulted,
                then the “name=value” variable assignments recognized in
                item 1 affect the current shell.

           3.   Redirections are performed as described in the next
                section.

   Redirections
     Redirections are used to change where a command reads its input or
     sends its output.  In general, redirections open, close, or
     duplicate an existing reference to a file.  The overall format used
     for redirection is:

           [n] redir-op file

     where redir-op is one of the redirection operators mentioned
     previously.  Following is a list of the possible redirections.  The
     [n] is an optional number between 0 and 9, as in ‘3’ (not ‘[3]’),
     that refers to a file descriptor.

           [n]> file   Redirect standard output (or n) to file.

           [n]>| file  Same, but override the -C option.

           [n]>> file  Append standard output (or n) to file.

           [n]< file   Redirect standard input (or n) from file.

           [n1]<&n2    Copy file descriptor n2 as stdout (or fd n1).  fd
                       n2.

           [n]<&-      Close standard input (or n).

           [n1]>&n2    Copy file descriptor n2 as stdin (or fd n1).  fd
                       n2.

           [n]>&-      Close standard output (or n).

           [n]<> file  Open file for reading and writing on standard
                       input (or n).

     The following redirection is often called a “here-document”.

           [n]<< delimiter
                 here-doc-text ...
           delimiter

     All the text on successive lines up to the delimiter is saved away
     and made available to the command on standard input, or file
     descriptor n if it is specified.  If the delimiter as specified on
     the initial line is quoted, then the here-doc-text is treated
     literally, otherwise the text is subjected to parameter expansion,
     command substitution, and arithmetic expansion (as described in the
     section on “Expansions”).  If the operator is “<<-” instead of
     “<<”, then leading tabs in the here-doc-text are stripped.

   Search and Execution
     There are three types of commands: shell functions, builtin
     commands, and normal programs – and the command is searched for (by
     name) in that order.  They each are executed in a different way.

     When a shell function is executed, all of the shell positional
     parameters (except $0, which remains unchanged) are set to the
     arguments of the shell function.  The variables which are
     explicitly placed in the environment of the command (by placing
     assignments to them before the function name) are made local to the
     function and are set to the values given.  Then the command given
     in the function definition is executed.  The positional parameters
     are restored to their original values when the command completes.
     This all occurs within the current shell.

     Shell builtins are executed internally to the shell, without
     spawning a new process.

     Otherwise, if the command name doesn't match a function or builtin,
     the command is searched for as a normal program in the file system
     (as described in the next section).  When a normal program is
     executed, the shell runs the program, passing the arguments and the
     environment to the program.  If the program is not a normal
     executable file (i.e., if it does not begin with the "magic number"
     whose ASCII representation is "#!", so execve(2) returns ENOEXEC
     then) the shell will interpret the program in a subshell.  The
     child shell will reinitialize itself in this case, so that the
     effect will be as if a new shell had been invoked to handle the ad-
     hoc shell script, except that the location of hashed commands
     located in the parent shell will be remembered by the child.

     Note that previous versions of this document and the source code
     itself misleadingly and sporadically refer to a shell script
     without a magic number as a "shell procedure".

   Path Search
     When locating a command, the shell first looks to see if it has a
     shell function by that name.  Then it looks for a builtin command
     by that name.  If a builtin command is not found, one of two things
     happen:

     1.   Command names containing a slash are simply executed without
          performing any searches.

     2.   The shell searches each entry in PATH in turn for the command.
          The value of the PATH variable should be a series of entries
          separated by colons.  Each entry consists of a directory name.
          The current directory may be indicated implicitly by an empty
          directory name, or explicitly by a single period.

   Command Exit Status
     Each command has an exit status that can influence the behaviour of
     other shell commands.  The paradigm is that a command exits with
     zero for normal or success, and non-zero for failure, error, or a
     false indication.  The man page for each command should indicate
     the various exit codes and what they mean.  Additionally, the
     builtin commands return exit codes, as does an executed shell
     function.

     If a command consists entirely of variable assignments then the
     exit status of the command is that of the last command substitution
     if any, otherwise 0.

   Complex Commands
     Complex commands are combinations of simple commands with control
     operators or reserved words, together creating a larger complex
     command.  More generally, a command is one of the following:

     simple command

     pipeline

     list or compound-list

     compound command

     function definition

     Unless otherwise stated, the exit status of a command is that of
     the last simple command executed by the command.

   Pipelines
     A pipeline is a sequence of one or more commands separated by the
     control operator |.  The standard output of all but the last
     command is connected to the standard input of the next command.
     The standard output of the last command is inherited from the
     shell, as usual.

     The format for a pipeline is:

           [!] command1 [| command2 ...]

     The standard output of command1 is connected to the standard input
     of command2.  The standard input, standard output, or both of a
     command is considered to be assigned by the pipeline before any
     redirection specified by redirection operators that are part of the
     command.

     If the pipeline is not in the background (discussed later), the
     shell waits for all commands to complete.

     If the reserved word ! does not precede the pipeline, the exit
     status is the exit status of the last command specified in the
     pipeline.  Otherwise, the exit status is the logical NOT of the
     exit status of the last command.  That is, if the last command
     returns zero, the exit status is 1; if the last command returns
     greater than zero, the exit status is zero.

     Because pipeline assignment of standard input or standard output or
     both takes place before redirection, it can be modified by
     redirection.  For example:

           $ command1 2>&1 | command2

     sends both the standard output and standard error of command1 to
     the standard input of command2.

     A ; or ⟨newline⟩ terminator causes the preceding AND-OR-list
     (described next) to be executed sequentially; a & causes
     asynchronous execution of the preceding AND-OR-list.

     Note that unlike some other shells, each process in the pipeline is
     a child of the invoking shell (unless it is a shell builtin, in
     which case it executes in the current shell – but any effect it has
     on the environment is wiped).

   Background Commands – &
     If a command is terminated by the control operator ampersand (&),
     the shell executes the command asynchronously – that is, the shell
     does not wait for the command to finish before executing the next
     command.

     The format for running a command in background is:

           command1 & [command2 & ...]

     If the shell is not interactive, the standard input of an
     asynchronous command is set to /dev/null.

   Lists – Generally Speaking
     A list is a sequence of zero or more commands separated by
     newlines, semicolons, or ampersands, and optionally terminated by
     one of these three characters.  The commands in a list are executed
     in the order they are written.  If command is followed by an
     ampersand, the shell starts the command and immediately proceeds
     onto the next command; otherwise it waits for the command to
     terminate before proceeding to the next one.

   Short-Circuit List Operators
     “&&” and “||” are AND-OR list operators.  “&&” executes the first
     command, and then executes the second command if and only if the
     exit status of the first command is zero.  “||” is similar, but
     executes the second command if and only if the exit status of the
     first command is nonzero.  “&&” and “||” both have the same
     priority.

   Flow-Control Constructs – if, while, for, case
     The syntax of the if command is

           if list
           then list
           [ elif list
           then    list ] ...
           [ else list ]
           fi

     The syntax of the while command is

           while list
           do   list
           done

     The two lists are executed repeatedly while the exit status of the
     first list is zero.  The until command is similar, but has the word
     until in place of while, which causes it to repeat until the exit
     status of the first list is zero.

     The syntax of the for command is

           for variable [ in [ word ... ] ]
           do   list
           done

     The words following in are expanded, and then the list is executed
     repeatedly with the variable set to each word in turn.  Omitting in
     word ... is equivalent to in "$@".

     The syntax of the break and continue command is

           break [ num ]
           continue [ num ]

     Break terminates the num innermost for or while loops.  Continue
     continues with the next iteration of the innermost loop.  These are
     implemented as builtin commands.

     The syntax of the case command is

           case word in
           [(]pattern) list ;;
           ...
           esac

     The pattern can actually be one or more patterns (see Shell
     Patterns described later), separated by “|” characters.  The “(”
     character before the pattern is optional.

   Grouping Commands Together
     Commands may be grouped by writing either

           (list)

     or

           { list; }

     The first of these executes the commands in a subshell.  Builtin
     commands grouped into a (list) will not affect the current shell.
     The second form does not fork another shell so is slightly more
     efficient.  Grouping commands together this way allows you to
     redirect their output as though they were one program:

           { printf " hello " ; printf " world\n" ; } > greeting

     Note that “}” must follow a control operator (here, “;”) so that it
     is recognized as a reserved word and not as another command
     argument.

   Functions
     The syntax of a function definition is

           name () command

     A function definition is an executable statement; when executed it
     installs a function named name and returns an exit status of zero.
     The command is normally a list enclosed between “{” and “}”.

     Variables may be declared to be local to a function by using a
     local command.  This should appear as the first statement of a
     function, and the syntax is

           local [variable | -] ...

     Local is implemented as a builtin command.

     When a variable is made local, it inherits the initial value and
     exported and readonly flags from the variable with the same name in
     the surrounding scope, if there is one.  Otherwise, the variable is
     initially unset.  The shell uses dynamic scoping, so that if you
     make the variable x local to function f, which then calls function
     g, references to the variable x made inside g will refer to the
     variable x declared inside f, not to the global variable named x.

     The only special parameter that can be made local is “-”.  Making
     “-” local any shell options that are changed via the set command
     inside the function to be restored to their original values when
     the function returns.

     The syntax of the return command is

           return [exitstatus]

     It terminates the currently executing function.  Return is
     implemented as a builtin command.

   Variables and Parameters
     The shell maintains a set of parameters.  A parameter denoted by a
     name is called a variable.  When starting up, the shell turns all
     the environment variables into shell variables.  New variables can
     be set using the form

           name=value

     Variables set by the user must have a name consisting solely of
     alphabetics, numerics, and underscores - the first of which must
     not be numeric.  A parameter can also be denoted by a number or a
     special character as explained below.

   Positional Parameters
     A positional parameter is a parameter denoted by a number (n > 0).
     The shell sets these initially to the values of its command line
     arguments that follow the name of the shell script.  The set
     builtin can also be used to set or reset them.

   Special Parameters
     A special parameter is a parameter denoted by one of the following
     special characters.  The value of the parameter is listed next to
     its character.

     *            Expands to the positional parameters, starting from
                  one.  When the expansion occurs within a double-quoted
                  string it expands to a single field with the value of
                  each parameter separated by the first character of the
                  IFS variable, or by a ⟨space⟩ if IFS is unset.

     @            Expands to the positional parameters, starting from
                  one.  When the expansion occurs within double-quotes,
                  each positional parameter expands as a separate
                  argument.  If there are no positional parameters, the
                  expansion of @ generates zero arguments, even when @
                  is double-quoted.  What this basically means, for
                  example, is if $1 is “abc” and $2 is “def ghi”, then
                  "$@" expands to the two arguments:

                        "abc" "def ghi"

     #            Expands to the number of positional parameters.

     ?            Expands to the exit status of the most recent
                  pipeline.

     - (Hyphen.)  Expands to the current option flags (the single-letter
                  option names concatenated into a string) as specified
                  on invocation, by the set builtin command, or
                  implicitly by the shell.

     $            Expands to the process ID of the invoked shell.  A
                  subshell retains the same value of $ as its parent.

     !            Expands to the process ID of the most recent
                  background command executed from the current shell.
                  For a pipeline, the process ID is that of the last
                  command in the pipeline.

     0 (Zero.)    Expands to the name of the shell or shell script.

   Word Expansions
     This clause describes the various expansions that are performed on
     words.  Not all expansions are performed on every word, as
     explained later.

     Tilde expansions, parameter expansions, command substitutions,
     arithmetic expansions, and quote removals that occur within a
     single word expand to a single field.  It is only field splitting
     or pathname expansion that can create multiple fields from a single
     word.  The single exception to this rule is the expansion of the
     special parameter @ within double-quotes, as was described above.

     The order of word expansion is:

     1.   Tilde Expansion, Parameter Expansion, Command Substitution,
          Arithmetic Expansion (these all occur at the same time).

     2.   Field Splitting is performed on fields generated by step (1)
          unless the IFS variable is null.

     3.   Pathname Expansion (unless set -f is in effect).

     4.   Quote Removal.

     The $ character is used to introduce parameter expansion, command
     substitution, or arithmetic evaluation.

   Tilde Expansion (substituting a user's home directory)
     A word beginning with an unquoted tilde character (~) is subjected
     to tilde expansion.  All the characters up to a slash (/) or the
     end of the word are treated as a username and are replaced with the
     user's home directory.  If the username is missing (as in
     ~/foobar), the tilde is replaced with the value of the HOME
     variable (the current user's home directory).

   Parameter Expansion
     The format for parameter expansion is as follows:

           ${expression}

     where expression consists of all characters until the matching “}”.
     Any “}” escaped by a backslash or within a quoted string, and
     characters in embedded arithmetic expansions, command
     substitutions, and variable expansions, are not examined in
     determining the matching “}”.

     The simplest form for parameter expansion is:

           ${parameter}

     The value, if any, of parameter is substituted.

     The parameter name or symbol can be enclosed in braces, which are
     optional except for positional parameters with more than one digit
     or when parameter is followed by a character that could be
     interpreted as part of the name.  If a parameter expansion occurs
     inside double-quotes:

     1.   Pathname expansion is not performed on the results of the
          expansion.

     2.   Field splitting is not performed on the results of the
          expansion, with the exception of @.

     In addition, a parameter expansion can be modified by using one of
     the following formats.

     ${parameter:-word}    Use Default Values.  If parameter is unset or
                           null, the expansion of word is substituted;
                           otherwise, the value of parameter is
                           substituted.

     ${parameter:=word}    Assign Default Values.  If parameter is unset
                           or null, the expansion of word is assigned to
                           parameter.  In all cases, the final value of
                           parameter is substituted.  Only variables,
                           not positional parameters or special
                           parameters, can be assigned in this way.

     ${parameter:?[word]}  Indicate Error if Null or Unset.  If
                           parameter is unset or null, the expansion of
                           word (or a message indicating it is unset if
                           word is omitted) is written to standard error
                           and the shell exits with a nonzero exit
                           status.  Otherwise, the value of parameter is
                           substituted.  An interactive shell need not
                           exit.

     ${parameter:+word}    Use Alternative Value.  If parameter is unset
                           or null, null is substituted; otherwise, the
                           expansion of word is substituted.

     In the parameter expansions shown previously, use of the colon in
     the format results in a test for a parameter that is unset or null;
     omission of the colon results in a test for a parameter that is
     only unset.

     ${#parameter}         String Length.  The length in characters of
                           the value of parameter.

     The following four varieties of parameter expansion provide for
     substring processing.  In each case, pattern matching notation (see
     Shell Patterns), rather than regular expression notation, is used
     to evaluate the patterns.  If parameter is * or @, the result of
     the expansion is unspecified.  Enclosing the full parameter
     expansion string in double-quotes does not cause the following four
     varieties of pattern characters to be quoted, whereas quoting
     characters within the braces has this effect.

     ${parameter%word}     Remove Smallest Suffix Pattern.  The word is
                           expanded to produce a pattern.  The parameter
                           expansion then results in parameter, with the
                           smallest portion of the suffix matched by the
                           pattern deleted.

     ${parameter%%word}    Remove Largest Suffix Pattern.  The word is
                           expanded to produce a pattern.  The parameter
                           expansion then results in parameter, with the
                           largest portion of the suffix matched by the
                           pattern deleted.

     ${parameter#word}     Remove Smallest Prefix Pattern.  The word is
                           expanded to produce a pattern.  The parameter
                           expansion then results in parameter, with the
                           smallest portion of the prefix matched by the
                           pattern deleted.

     ${parameter##word}    Remove Largest Prefix Pattern.  The word is
                           expanded to produce a pattern.  The parameter
                           expansion then results in parameter, with the
                           largest portion of the prefix matched by the
                           pattern deleted.

   Command Substitution
     Command substitution allows the output of a command to be
     substituted in place of the command name itself.  Command
     substitution occurs when the command is enclosed as follows:

           $(command)

     or (“backquoted” version):

           `command`

     The shell expands the command substitution by executing command in
     a subshell environment and replacing the command substitution with
     the standard output of the command, removing sequences of one or
     more ⟨newline⟩s at the end of the substitution.  (Embedded
     ⟨newline⟩s before the end of the output are not removed; however,
     during field splitting, they may be translated into ⟨space⟩s,
     depending on the value of IFS and quoting that is in effect.)

   Arithmetic Expansion
     Arithmetic expansion provides a mechanism for evaluating an
     arithmetic expression and substituting its value.  The format for
     arithmetic expansion is as follows:

           $((expression))

     The expression is treated as if it were in double-quotes, except
     that a double-quote inside the expression is not treated specially.
     The shell expands all tokens in the expression for parameter
     expansion, command substitution, and quote removal.

     Next, the shell treats this as an arithmetic expression and
     substitutes the value of the expression.

   White Space Splitting (Field Splitting)
     After parameter expansion, command substitution, and arithmetic
     expansion the shell scans the results of expansions and
     substitutions that did not occur in double-quotes for field
     splitting and multiple fields can result.

     The shell treats each character of the IFS as a delimiter and uses
     the delimiters to split the results of parameter expansion and
     command substitution into fields.

   Pathname Expansion (File Name Generation)
     Unless the -f flag is set, file name generation is performed after
     word splitting is complete.  Each word is viewed as a series of
     patterns, separated by slashes.  The process of expansion replaces
     the word with the names of all existing files whose names can be
     formed by replacing each pattern with a string that matches the
     specified pattern.  There are two restrictions on this: first, a
     pattern cannot match a string containing a slash, and second, a
     pattern cannot match a string starting with a period unless the
     first character of the pattern is a period.  The next section
     describes the patterns used for both Pathname Expansion and the
     case command.

   Shell Patterns
     A pattern consists of normal characters, which match themselves,
     and meta-characters.  The meta-characters are “!”, “*”, “?”, and
     “[”.  These characters lose their special meanings if they are
     quoted.  When command or variable substitution is performed and the
     dollar sign or back quotes are not double quoted, the value of the
     variable or the output of the command is scanned for these
     characters and they are turned into meta-characters.

     An asterisk (“*”) matches any string of characters.  A question
     mark matches any single character.  A left bracket (“[”) introduces
     a character class.  The end of the character class is indicated by
     a (“]”); if the “]” is missing then the “[” matches a “[” rather
     than introducing a character class.  A character class matches any
     of the characters between the square brackets.  A range of
     characters may be specified using a minus sign.  The character
     class may be complemented by making an exclamation point the first
     character of the character class.

     To include a “]” in a character class, make it the first character
     listed (after the “!”, if any).  To include a minus sign, make it
     the first or last character listed.

   Builtins
     This section lists the builtin commands which are builtin because
     they need to perform some operation that can't be performed by a
     separate process.  In addition to these, there are several other
     commands that may be builtin for efficiency (e.g.  printf(1),
     echo(1), test(1), etc).

     :

     true   A null command that returns a 0 (true) exit value.

     . file
            The commands in the specified file are read and executed by
            the shell.

     alias [name[=string ...]]
            If name=string is specified, the shell defines the alias
            name with value string.  If just name is specified, the
            value of the alias name is printed.  With no arguments, the
            alias builtin prints the names and values of all defined
            aliases (see unalias).

     bg [job] ...
            Continue the specified jobs (or the current job if no jobs
            are given) in the background.

     command [-p] [-v] [-V] command [arg ...]
            Execute the specified command but ignore shell functions
            when searching for it.  (This is useful when you have a
            shell function with the same name as a builtin command.)

            -p     search for command using a PATH that guarantees to
                   find all the standard utilities.

            -V     Do not execute the command but search for the command
                   and print the resolution of the command search.  This
                   is the same as the type builtin.

            -v     Do not execute the command but search for the command
                   and print the absolute pathname of utilities, the
                   name for builtins or the expansion of aliases.

     cd -

     cd [-LP] [directory]
            Switch to the specified directory (default HOME).  If an
            entry for CDPATH appears in the environment of the cd
            command or the shell variable CDPATH is set and the
            directory name does not begin with a slash, then the
            directories listed in CDPATH will be searched for the
            specified directory.  The format of CDPATH is the same as
            that of PATH.  If a single dash is specified as the
            argument, it will be replaced by the value of OLDPWD.  The
            cd command will print out the name of the directory that it
            actually switched to if this is different from the name that
            the user gave.  These may be different either because the
            CDPATH mechanism was used or because the argument is a
            single dash.  The -P option causes the physical directory
            structure to be used, that is, all symbolic links are
            resolved to their respective values.  The -L option turns
            off the effect of any preceding -P options.

     echo [-n] args...
            Print the arguments on the standard output, separated by
            spaces.  Unless the -n option is present, a newline is
            output following the arguments.

            If any of the following sequences of characters is
            encountered during output, the sequence is not output.
            Instead, the specified action is performed:

            \b      A backspace character is output.

            \c      Subsequent output is suppressed.  This is normally
                    used at the end of the last argument to suppress the
                    trailing newline that echo would otherwise output.

            \f      Output a form feed.

            \n      Output a newline character.

            \r      Output a carriage return.

            \t      Output a (horizontal) tab character.

            \v      Output a vertical tab.

            \0digits
                    Output the character whose value is given by zero to
                    three octal digits.  If there are zero digits, a nul
                    character is output.

            \\      Output a backslash.

            All other backslash sequences elicit undefined behaviour.

     eval string ...
            Concatenate all the arguments with spaces.  Then re-parse
            and execute the command.

     exec [command arg ...]
            Unless command is omitted, the shell process is replaced
            with the specified program (which must be a real program,
            not a shell builtin or function).  Any redirections on the
            exec command are marked as permanent, so that they are not
            undone when the exec command finishes.

     exit [exitstatus]
            Terminate the shell process.  If exitstatus is given it is
            used as the exit status of the shell; otherwise the exit
            status of the preceding command is used.

     export name ...

     export -p
            The specified names are exported so that they will appear in
            the environment of subsequent commands.  The only way to un-
            export a variable is to unset it.  The shell allows the
            value of a variable to be set at the same time it is
            exported by writing

                  export name=value

            With no arguments the export command lists the names of all
            exported variables.  With the -p option specified the output
            will be formatted suitably for non-interactive use.

     fc [-e editor] [first [last]]

     fc -l [-nr] [first [last]]

     fc -s [old=new] [first]
            The fc builtin lists, or edits and re-executes, commands
            previously entered to an interactive shell.

            -e editor
                   Use the editor named by editor to edit the commands.
                   The editor string is a command name, subject to
                   search via the PATH variable.  The value in the
                   FCEDIT variable is used as a default when -e is not
                   specified.  If FCEDIT is null or unset, the value of
                   the EDITOR variable is used.  If EDITOR is null or
                   unset, ed(1) is used as the editor.

            -l (ell)
                   List the commands rather than invoking an editor on
                   them.  The commands are written in the sequence
                   indicated by the first and last operands, as affected
                   by -r, with each command preceded by the command
                   number.

            -n     Suppress command numbers when listing with -l.

            -r     Reverse the order of the commands listed (with -l) or
                   edited (with neither -l nor -s).

            -s     Re-execute the command without invoking an editor.

            first

            last   Select the commands to list or edit.  The number of
                   previous commands that can be accessed are determined
                   by the value of the HISTSIZE variable.  The value of
                   first or last or both are one of the following:

                   [+]number
                          A positive number representing a command
                          number; command numbers can be displayed with
                          the -l option.

                   -number
                          A negative decimal number representing the
                          command that was executed number of commands
                          previously.  For example, -1 is the
                          immediately previous command.

            string
                   A string indicating the most recently entered command
                   that begins with that string.  If the old=new operand
                   is not also specified with -s, the string form of the
                   first operand cannot contain an embedded equal sign.

            The following environment variables affect the execution of
            fc:

            FCEDIT    Name of the editor to use.

            HISTSIZE  The number of previous commands that are
                      accessible.

     fg [job]
            Move the specified job or the current job to the foreground.

     getopts optstring var
            The POSIX getopts command, not to be confused with the Bell
            Labs -derived getopt(1).

            The first argument should be a series of letters, each of
            which may be optionally followed by a colon to indicate that
            the option requires an argument.  The variable specified is
            set to the parsed option.

            The getopts command deprecates the older getopt(1) utility
            due to its handling of arguments containing whitespace.

            The getopts builtin may be used to obtain options and their
            arguments from a list of parameters.  When invoked, getopts
            places the value of the next option from the option string
            in the list in the shell variable specified by var and its
            index in the shell variable OPTIND.  When the shell is
            invoked, OPTIND is initialized to 1.  For each option that
            requires an argument, the getopts builtin will place it in
            the shell variable OPTARG.  If an option is not allowed for
            in the optstring, then OPTARG will be unset.

            optstring is a string of recognized option letters (see
            getopt(3)).  If a letter is followed by a colon, the option
            is expected to have an argument which may or may not be
            separated from it by white space.  If an option character is
            not found where expected, getopts will set the variable var
            to a “?”; getopts will then unset OPTARG and write output to
            standard error.  By specifying a colon as the first
            character of optstring all errors will be ignored.

            After the last option getopts will return a non-zero value
            and set var to “?”.

            The following code fragment shows how one might process the
            arguments for a command that can take the options [a] and
            [b], and the option [c], which requires an argument.

                  while getopts abc: f
                  do
                          case $f in
                          a | b)  flag=$f;;
                          c)      carg=$OPTARG;;
                          \?)     echo $USAGE; exit 1;;
                          esac
                  done
                  shift `expr $OPTIND - 1`

            This code will accept any of the following as equivalent:

                  cmd -acarg file file
                  cmd -a -c arg file file
                  cmd -carg -a file file
                  cmd -a -carg -- file file

     hash -rv command ...
            The shell maintains a hash table which remembers the
            locations of commands.  With no arguments whatsoever, the
            hash command prints out the contents of this table.  Entries
            which have not been looked at since the last cd command are
            marked with an asterisk; it is possible for these entries to
            be invalid.

            With arguments, the hash command removes the specified
            commands from the hash table (unless they are functions) and
            then locates them.  With the -v option, hash prints the
            locations of the commands as it finds them.  The -r option
            causes the hash command to delete all the entries in the
            hash table except for functions.

     pwd [-LP]
            builtin command remembers what the current directory is
            rather than recomputing it each time.  This makes it faster.
            However, if the current directory is renamed, the builtin
            version of pwd will continue to print the old name for the
            directory.  The -P option causes the physical value of the
            current working directory to be shown, that is, all symbolic
            links are resolved to their respective values.  The -L
            option turns off the effect of any preceding -P options.

     read [-p prompt] [-r] variable [...]
            The prompt is printed if the -p option is specified and the
            standard input is a terminal.  Then a line is read from the
            standard input.  The trailing newline is deleted from the
            line and the line is split as described in the section on
            word splitting above, and the pieces are assigned to the
            variables in order.  At least one variable must be
            specified.  If there are more pieces than variables, the
            remaining pieces (along with the characters in IFS that
            separated them) are assigned to the last variable.  If there
            are more variables than pieces, the remaining variables are
            assigned the null string.  The read builtin will indicate
            success unless EOF is encountered on input, in which case
            failure is returned.

            By default, unless the -r option is specified, the backslash
            “\” acts as an escape character, causing the following
            character to be treated literally.  If a backslash is
            followed by a newline, the backslash and the newline will be
            deleted.

     readonly name ...

     readonly -p
            The specified names are marked as read only, so that they
            cannot be subsequently modified or unset.  The shell allows
            the value of a variable to be set at the same time it is
            marked read only by writing

                  readonly name=value

            With no arguments the readonly command lists the names of
            all read only variables.  With the -p option specified the
            output will be formatted suitably for non-interactive use.

     printf format [arguments ...]
            printf formats and prints its arguments, after the first,
            under control of the format.  The format is a character
            string which contains three types of objects: plain
            characters, which are simply copied to standard output,
            character escape sequences which are converted and copied to
            the standard output, and format specifications, each of
            which causes printing of the next successive argument.

            The arguments after the first are treated as strings if the
            corresponding format is either b, c or s; otherwise it is
            evaluated as a C constant, with the following extensions:

                  A leading plus or minus sign is allowed.
                  If the leading character is a single or double
                      quote, the value is the ASCII code of the next
                      character.

            The format string is reused as often as necessary to satisfy
            the arguments.  Any extra format specifications are
            evaluated with zero or the null string.

            Character escape sequences are in backslash notation as
            defined in ANSI X3.159-1989 (“ANSI C89”).  The characters
            and their meanings are as follows:

                  \a      Write a <bell> character.

                  \b      Write a <backspace> character.

                  \f      Write a <form-feed> character.

                  \n      Write a <new-line> character.

                  \r      Write a <carriage return> character.

                  \t      Write a <tab> character.

                  \v      Write a <vertical tab> character.

                  \\      Write a backslash character.

                  \num    Write an 8-bit character whose ASCII value is
                          the 1-, 2-, or 3-digit octal number num.

            Each format specification is introduced by the percent
            character (``%'').  The remainder of the format
            specification includes, in the following order:

            Zero or more of the following flags:

                    #       A `#' character specifying that the value
                            should be printed in an ``alternative
                            form''.  For b, c, d, and s formats, this
                            option has no effect.  For the o format the
                            precision of the number is increased to
                            force the first character of the output
                            string to a zero.  For the x (X) format, a
                            non-zero result has the string 0x (0X)
                            prepended to it.  For e, E, f, g, and G
                            formats, the result will always contain a
                            decimal point, even if no digits follow the
                            point (normally, a decimal point only
                            appears in the results of those formats if a
                            digit follows the decimal point).  For g and
                            G formats, trailing zeros are not removed
                            from the result as they would otherwise be.

                    -       A minus sign `-' which specifies left
                            adjustment of the output in the indicated
                            field;

                    +       A `+' character specifying that there should
                            always be a sign placed before the number
                            when using signed formats.

                    ‘ ’     A space specifying that a blank should be
                            left before a positive number for a signed
                            format.  A `+' overrides a space if both are
                            used;

                    0       A zero `0' character indicating that zero-
                            padding should be used rather than blank-
                            padding.  A `-' overrides a `0' if both are
                            used;

            Field Width:
                    An optional digit string specifying a field width;
                    if the output string has fewer characters than the
                    field width it will be blank-padded on the left (or
                    right, if the left-adjustment indicator has been
                    given) to make up the field width (note that a
                    leading zero is a flag, but an embedded zero is part
                    of a field width);

            Precision:
                    An optional period, ‘.’, followed by an optional
                    digit string giving a precision which specifies the
                    number of digits to appear after the decimal point,
                    for e and f formats, or the maximum number of bytes
                    to be printed from a string (b and s formats); if
                    the digit string is missing, the precision is
                    treated as zero;

            Format:
                    A character which indicates the type of format to
                    use (one of diouxXfwEgGbcs).

            A field width or precision may be ‘*’ instead of a digit
            string.  In this case an argument supplies the field width
            or precision.

            The format characters and their meanings are:

            diouXx      The argument is printed as a signed decimal (d
                        or i), unsigned octal, unsigned decimal, or
                        unsigned hexadecimal (X or x), respectively.

            f           The argument is printed in the style [-]ddd.ddd
                        where the number of d's after the decimal point
                        is equal to the precision specification for the
                        argument.  If the precision is missing, 6 digits
                        are given; if the precision is explicitly 0, no
                        digits and no decimal point are printed.

            eE          The argument is printed in the style
                        [-]d.ddde±dd where there is one digit before the
                        decimal point and the number after is equal to
                        the precision specification for the argument;
                        when the precision is missing, 6 digits are
                        produced.  An upper-case E is used for an `E'
                        format.

            gG          The argument is printed in style f or in style e
                        (E) whichever gives full precision in minimum
                        space.

            b           Characters from the string argument are printed
                        with backslash-escape sequences expanded.
                        The following additional backslash-escape
                        sequences are supported:

                        \c      Causes dash to ignore any remaining
                                characters in the string operand
                                containing it, any remaining string
                                operands, and any additional characters
                                in the format operand.

                        \0num   Write an 8-bit character whose ASCII
                                value is the 1-, 2-, or 3-digit octal
                                number num.

            c           The first character of argument is printed.

            s           Characters from the string argument are printed
                        until the end is reached or until the number of
                        bytes indicated by the precision specification
                        is reached; if the precision is omitted, all
                        characters in the string are printed.

            %           Print a `%'; no argument is used.

            In no case does a non-existent or small field width cause
            truncation of a field; padding takes place only if the
            specified field width exceeds the actual width.

     set [{ -options | +options | -- }] arg ...
            The set command performs three different functions.

            With no arguments, it lists the values of all shell
            variables.

            If options are given, it sets the specified option flags, or
            clears them as described in the section called Argument List
            Processing.  As a special case, if the option is -o or +o
            and no argument is supplied, the shell prints the settings
            of all its options.  If the option is -o, the settings are
            printed in a human-readable format; if the option is +o, the
            settings are printed in a format suitable for reinput to the
            shell to affect the same option settings.

            The third use of the set command is to set the values of the
            shell's positional parameters to the specified args.  To
            change the positional parameters without changing any
            options, use “--” as the first argument to set.  If no args
            are present, the set command will clear all the positional
            parameters (equivalent to executing “shift $#”.)

     shift [n]
            Shift the positional parameters n times.  A shift sets the
            value of $1 to the value of $2, the value of $2 to the value
            of $3, and so on, decreasing the value of $# by one.  If n
            is greater than the number of positional parameters, shift
            will issue an error message, and exit with return status 2.

     test expression

     [ expression ]
            The test utility evaluates the expression and, if it
            evaluates to true, returns a zero (true) exit status;
            otherwise it returns 1 (false).  If there is no expression,
            test also returns 1 (false).

            All operators and flags are separate arguments to the test
            utility.

            The following primaries are used to construct expression:

            -b file       True if file exists and is a block special
                          file.

            -c file       True if file exists and is a character special
                          file.

            -d file       True if file exists and is a directory.

            -e file       True if file exists (regardless of type).

            -f file       True if file exists and is a regular file.

            -g file       True if file exists and its set group ID flag
                          is set.

            -h file       True if file exists and is a symbolic link.

            -k file       True if file exists and its sticky bit is set.

            -n string     True if the length of string is nonzero.

            -p file       True if file is a named pipe (FIFO).

            -r file       True if file exists and is readable.

            -s file       True if file exists and has a size greater
                          than zero.

            -t file_descriptor
                          True if the file whose file descriptor number
                          is file_descriptor is open and is associated
                          with a terminal.

            -u file       True if file exists and its set user ID flag
                          is set.

            -w file       True if file exists and is writable.  True
                          indicates only that the write flag is on.  The
                          file is not writable on a read-only file
                          system even if this test indicates true.

            -x file       True if file exists and is executable.  True
                          indicates only that the execute flag is on.
                          If file is a directory, true indicates that
                          file can be searched.

            -z string     True if the length of string is zero.

            -L file       True if file exists and is a symbolic link.
                          This operator is retained for compatibility
                          with previous versions of this program.  Do
                          not rely on its existence; use -h instead.

            -O file       True if file exists and its owner matches the
                          effective user id of this process.

            -G file       True if file exists and its group matches the
                          effective group id of this process.

            -S file       True if file exists and is a socket.

            file1 -nt file2
                          True if file1 and file2 exist and file1 is
                          newer than file2.

            file1 -ot file2
                          True if file1 and file2 exist and file1 is
                          older than file2.

            file1 -ef file2
                          True if file1 and file2 exist and refer to the
                          same file.

            string        True if string is not the null string.

            s1 = s2       True if the strings s1 and s2 are identical.

            s1 != s2      True if the strings s1 and s2 are not
                          identical.

            s1 < s2       True if string s1 comes before s2 based on the
                          ASCII value of their characters.

            s1 > s2       True if string s1 comes after s2 based on the
                          ASCII value of their characters.

            n1 -eq n2     True if the integers n1 and n2 are
                          algebraically equal.

            n1 -ne n2     True if the integers n1 and n2 are not
                          algebraically equal.

            n1 -gt n2     True if the integer n1 is algebraically
                          greater than the integer n2.

            n1 -ge n2     True if the integer n1 is algebraically
                          greater than or equal to the integer n2.

            n1 -lt n2     True if the integer n1 is algebraically less
                          than the integer n2.

            n1 -le n2     True if the integer n1 is algebraically less
                          than or equal to the integer n2.

            These primaries can be combined with the following
            operators:

            ! expression  True if expression is false.

            expression1 -a expression2
                          True if both expression1 and expression2 are
                          true.

            expression1 -o expression2
                          True if either expression1 or expression2 are
                          true.

            (expression)  True if expression is true.

            The -a operator has higher precedence than the -o operator.

     times  Print the accumulated user and system times for the shell
            and for processes run from the shell.  The return status is
            0.

     trap [action signal ...]
            Cause the shell to parse and execute action when any of the
            specified signals are received.  The signals are specified
            by signal number or as the name of the signal.  If signal is
            0 or EXIT, the action is executed when the shell exits.
            action may be empty (''), which causes the specified signals
            to be ignored.  With action omitted or set to `-' the
            specified signals are set to their default action.  When the
            shell forks off a subshell, it resets trapped (but not
            ignored) signals to the default action.  The trap command
            has no effect on signals that were ignored on entry to the
            shell.  trap without any arguments cause it to write a list
            of signals and their associated action to the standard
            output in a format that is suitable as an input to the shell
            that achieves the same trapping results.

            Examples:

                  trap

            List trapped signals and their corresponding action

                  trap '' INT QUIT tstp 30

            Ignore signals INT QUIT TSTP USR1

                  trap date INT

            Print date upon receiving signal INT

     type [name ...]
            Interpret each name as a command and print the resolution of
            the command search.  Possible resolutions are: shell
            keyword, alias, shell builtin, command, tracked alias and
            not found.  For aliases the alias expansion is printed; for
            commands and tracked aliases the complete pathname of the
            command is printed.

     ulimit [-H | -S] [-a | -tfdscmlpnv [value]]
            Inquire about or set the hard or soft limits on processes or
            set new limits.  The choice between hard limit (which no
            process is allowed to violate, and which may not be raised
            once it has been lowered) and soft limit (which causes
            processes to be signaled but not necessarily killed, and
            which may be raised) is made with these flags:

            -H          set or inquire about hard limits

            -S          set or inquire about soft limits.  If neither -H
                        nor -S is specified, the soft limit is displayed
                        or both limits are set.  If both are specified,
                        the last one wins.

            The limit to be interrogated or set, then, is chosen by
            specifying any one of these flags:

            -a          show all the current limits

            -t          show or set the limit on CPU time (in seconds)

            -f          show or set the limit on the largest file that
                        can be created (in 512-byte blocks)

            -d          show or set the limit on the data segment size
                        of a process (in kilobytes)

            -s          show or set the limit on the stack size of a
                        process (in kilobytes)

            -c          show or set the limit on the largest core dump
                        size that can be produced (in 512-byte blocks)

            -m          show or set the limit on the total physical
                        memory that can be in use by a process (in
                        kilobytes)

            -l          show or set the limit on how much memory a
                        process can lock with mlock(2) (in kilobytes)

            -p          show or set the limit on the number of processes
                        this user can have at one time

            -n          show or set the limit on the number files a
                        process can have open at once

            -v          show or set the limit on the total virtual
                        memory that can be in use by a process (in
                        kilobytes)

            -r          show or set the limit on the real-time
                        scheduling priority of a process

            If none of these is specified, it is the limit on file size
            that is shown or set.  If value is specified, the limit is
            set to that number; otherwise the current limit is
            displayed.

            Limits of an arbitrary process can be displayed or set using
            the sysctl(8) utility.

     umask [mask]
            Set the value of umask (see umask(2)) to the specified octal
            value.  If the argument is omitted, the umask value is
            printed.

     unalias [-a] [name]
            If name is specified, the shell removes that alias.  If -a
            is specified, all aliases are removed.

     unset [-fv] name ...
            The specified variables and functions are unset and
            unexported.  If -f or -v is specified, the corresponding
            function or variable is unset, respectively.  If a given
            name corresponds to both a variable and a function, and no
            options are given, only the variable is unset.

     wait [job]
            Wait for the specified job to complete and return the exit
            status of the last process in the job.  If the argument is
            omitted, wait for all jobs to complete and return an exit
            status of zero.

   Command Line Editing
     When dash is being used interactively from a terminal, the current
     command and the command history (see fc in Builtins) can be edited
     using vi-mode command-line editing.  This mode uses commands,
     described below, similar to a subset of those described in the vi
     man page.  The command ‘set -o vi’ enables vi-mode editing and
     places sh into vi insert mode.  With vi-mode enabled, sh can be
     switched between insert mode and command mode.  It is similar to
     vi: typing ⟨ESC⟩ enters vi command mode.  Hitting ⟨return⟩ while in
     command mode will pass the line to the shell.

EXIT STATUS         top

     Errors that are detected by the shell, such as a syntax error, will
     cause the shell to exit with a non-zero exit status.  If the shell
     is not an interactive shell, the execution of the shell file will
     be aborted.  Otherwise the shell will return the exit status of the
     last command executed, or if the exit builtin is used with a
     numeric argument, it will return the argument.

ENVIRONMENT         top

     HOME       Set automatically by login(1) from the user's login
                directory in the password file (passwd(4)).  This
                environment variable also functions as the default
                argument for the cd builtin.

     PATH       The default search path for executables.  See the above
                section Path Search.

     CDPATH     The search path used with the cd builtin.

     MAIL       The name of a mail file, that will be checked for the
                arrival of new mail.  Overridden by MAILPATH.

     MAILCHECK  The frequency in seconds that the shell checks for the
                arrival of mail in the files specified by the MAILPATH
                or the MAIL file.  If set to 0, the check will occur at
                each prompt.

     MAILPATH   A colon “:” separated list of file names, for the shell
                to check for incoming mail.  This environment setting
                overrides the MAIL setting.  There is a maximum of 10
                mailboxes that can be monitored at once.

     PS1        The primary prompt string, which defaults to “$ ”,
                unless you are the superuser, in which case it defaults
                to “# ”.

     PS2        The secondary prompt string, which defaults to “> ”.

     PS4        Output before each line when execution trace (set -x) is
                enabled, defaults to “+ ”.

     IFS        Input Field Separators.  This is normally set to
                ⟨space⟩, ⟨tab⟩, and ⟨newline⟩.  See the White Space
                Splitting section for more details.

     TERM       The default terminal setting for the shell.  This is
                inherited by children of the shell, and is used in the
                history editing modes.

     HISTSIZE   The number of lines in the history buffer for the shell.

     PWD        The logical value of the current working directory.
                This is set by the cd command.

     OLDPWD     The previous logical value of the current working
                directory.  This is set by the cd command.

     PPID       The process ID of the parent process of the shell.

FILES         top

     $HOME/.profile

     /etc/profile

SEE ALSO         top

     csh(1), echo(1), getopt(1), ksh(1), login(1), printf(1), test(1),
     getopt(3), passwd(5), environ(7), sysctl(8)

HISTORY         top

     dash is a POSIX-compliant implementation of /bin/sh that aims to be
     as small as possible.  dash is a direct descendant of the NetBSD
     version of ash (the Almquist SHell), ported to Linux in early 1997.
     It was renamed to dash in 2002.

BUGS         top

     Setuid shell scripts should be avoided at all costs, as they are a
     significant security risk.

     PS1, PS2, and PS4 should be subject to parameter expansion before
     being displayed.

COLOPHON         top

     This page is part of the dash (Debian Almquist shell) project.
     Information about the project can be found at
     http://gondor.apana.org.au/~herbert/dash/.  If you have a bug
     report for this manual page, send it to dash@vger.kernel.org.  This
     page was obtained from the project's upstream Git repository
     ⟨git://git.kernel.org/pub/scm/utils/dash/dash.git⟩ on 2021-08-27.
     (At that time, the date of the most recent commit that was found in
     the repository was 2021-06-04.)  If you discover any rendering
     problems in this HTML version of the page, or you believe there is
     a better or more up-to-date source for the page, or you have
     corrections or improvements to the information in this COLOPHON
     (which is not part of the original manual page), send a mail to
     man-pages@man7.org

BSD                         January 19, 2003                         BSD

Pages that refer to this page: intro(1)systemctl(1)system(3)