touch(1p) — Linux manual page

PROLOG | NAME | SYNOPSIS | DESCRIPTION | OPTIONS | OPERANDS | STDIN | INPUT FILES | ENVIRONMENT VARIABLES | ASYNCHRONOUS EVENTS | STDOUT | STDERR | OUTPUT FILES | EXTENDED DESCRIPTION | EXIT STATUS | CONSEQUENCES OF ERRORS | APPLICATION USAGE | EXAMPLES | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT

TOUCH(1P)               POSIX Programmer's Manual              TOUCH(1P)

PROLOG         top

       This manual page is part of the POSIX Programmer's Manual.  The
       Linux implementation of this interface may differ (consult the
       corresponding Linux manual page for details of Linux behavior),
       or the interface may not be implemented on Linux.

NAME         top

       touch — change file access and modification times

SYNOPSIS         top

       touch [-acm] [-r ref_file|-t time|-d date_time] file...

DESCRIPTION         top

       The touch utility shall change the last data modification
       timestamps, the last data access timestamps, or both.

       The time used can be specified by the -t time option-argument,
       the corresponding time fields of the file referenced by the -r
       ref_file option-argument, or the -d date_time option-argument, as
       specified in the following sections. If none of these are
       specified, touch shall use the current time.

       For each file operand, touch shall perform actions equivalent to
       the following functions defined in the System Interfaces volume
       of POSIX.1‐2017:

        1. If file does not exist:

            a. The creat() function is called with the following
               arguments:

               --  The file operand is used as the path argument.

               --  The value of the bitwise-inclusive OR of S_IRUSR,
                   S_IWUSR, S_IRGRP, S_IWGRP, S_IROTH, and S_IWOTH is
                   used as the mode argument.

            b. The futimens() function is called with the following
               arguments:

               --  The file descriptor opened in step 1a.

               --  The access time and the modification time, set as
                   described in the OPTIONS section, are used as the
                   first and second elements of the times array
                   argument, respectively.

        2. If file exists, the utimensat() function is called with the
           following arguments:

            a. The AT_FDCWD special value is used as the fd argument.

            b. The file operand is used as the path argument.

            c. The access time and the modification time, set as
               described in the OPTIONS section, are used as the first
               and second elements of the times array argument,
               respectively.

            d. The flag argument is set to zero.

OPTIONS         top

       The touch utility shall conform to the Base Definitions volume of
       POSIX.1‐2017, Section 12.2, Utility Syntax Guidelines.

       The following options shall be supported:

       -a        Change the access time of file.  Do not change the
                 modification time unless -m is also specified.

       -c        Do not create a specified file if it does not exist. Do
                 not write any diagnostic messages concerning this
                 condition.

       -d date_time
                 Use the specified date_time instead of the current
                 time. The option-argument shall be a string of the
                 form:

                     YYYY-MM-DDThh:mm:SS[.frac][tz]

                 or:

                     YYYY-MM-DDThh:mm:SS[,frac][tz]

                 where:

                  *  YYYY are at least four decimal digits giving the
                     year.

                  *  MM, DD, hh, mm, and SS are as with -t time.

                  *  T is the time designator, and can be replaced by a
                     single <space>.

                  *  [.frac] and [,frac] are either empty, or a <period>
                     ('.')  or a <comma> (',') respectively, followed by
                     one or more decimal digits, specifying a fractional
                     second.

                  *  [tz] is either empty, signifying local time, or the
                     letter 'Z', signifying UTC. If [tz] is empty, the
                     resulting time shall be affected by the value of
                     the TZ environment variable.

                 If the resulting time precedes the Epoch, the behavior
                 is implementation-defined. If the time cannot be
                 represented as the file's timestamp, touch shall exit
                 immediately with an error status.

       -m        Change the modification time of file.  Do not change
                 the access time unless -a is also specified.

       -r ref_file
                 Use the corresponding time of the file named by the
                 pathname ref_file instead of the current time.

       -t time   Use the specified time instead of the current time. The
                 option-argument shall be a decimal number of the form:

                     [[CC]YY]MMDDhhmm[.SS]

                 where each two digits represents the following:

                 MM      The month of the year [01,12].

                 DD      The day of the month [01,31].

                 hh      The hour of the day [00,23].

                 mm      The minute of the hour [00,59].

                 CC      The first two digits of the year (the century).

                 YY      The second two digits of the year.

                 SS      The second of the minute [00,60].

                 Both CC and YY shall be optional. If neither is given,
                 the current year shall be assumed. If YY is specified,
                 but CC is not, CC shall be derived as follows:
                              ┌───────────┬─────────────┐
                              │ If YY is: CC becomes: │
                              ├───────────┼─────────────┤
                              │  [69,99]  │     19      │
                              │  [00,68]  │     20      │
                              └───────────┴─────────────┘

                 Note:  It is expected that in a future version of this
                        standard the default century inferred from a
                        2-digit year will change. (This would apply to
                        all commands accepting a 2-digit year as input.)

                 The resulting time shall be affected by the value of
                 the TZ environment variable. If the resulting time
                 value precedes the Epoch, the behavior is
                 implementation-defined. If the time is out of range for
                 the file's timestamp, touch shall exit immediately with
                 an error status. The range of valid times past the
                 Epoch is implementation-defined, but it shall extend to
                 at least the time 0 hours, 0 minutes, 0 seconds,
                 January 1, 2038, Coordinated Universal Time. Some
                 implementations may not be able to represent dates
                 beyond January 18, 2038, because they use signed int as
                 a time holder.

                 The range for SS is [00,60] rather than [00,59] because
                 of leap seconds. If SS is 60, and the resulting time,
                 as affected by the TZ environment variable, does not
                 refer to a leap second, the resulting time shall be one
                 second after a time where SS is 59. If SS is not given
                 a value, it is assumed to be zero.

       If neither the -a nor -m options were specified, touch shall
       behave as if both the -a and -m options were specified.

OPERANDS         top

       The following operands shall be supported:

       file      A pathname of a file whose times shall be modified.

STDIN         top

       Not used.

INPUT FILES         top

       None.

ENVIRONMENT VARIABLES         top

       The following environment variables shall affect the execution of
       touch:

       LANG      Provide a default value for the internationalization
                 variables that are unset or null. (See the Base
                 Definitions volume of POSIX.1‐2017, Section 8.2,
                 Internationalization Variables for the precedence of
                 internationalization variables used to determine the
                 values of locale categories.)

       LC_ALL    If set to a non-empty string value, override the values
                 of all the other internationalization variables.

       LC_CTYPE  Determine the locale for the interpretation of
                 sequences of bytes of text data as characters (for
                 example, single-byte as opposed to multi-byte
                 characters in arguments).

       LC_MESSAGES
                 Determine the locale that should be used to affect the
                 format and contents of diagnostic messages written to
                 standard error.

       NLSPATH   Determine the location of message catalogs for the
                 processing of LC_MESSAGES.

       TZ        Determine the timezone to be used for interpreting the
                 time option-argument. If TZ is unset or null, an
                 unspecified default timezone shall be used.

ASYNCHRONOUS EVENTS         top

       Default.

STDOUT         top

       Not used.

STDERR         top

       The standard error shall be used only for diagnostic messages.

OUTPUT FILES         top

       None.

EXTENDED DESCRIPTION         top

       None.

EXIT STATUS         top

       The following exit values shall be returned:

        0    The utility executed successfully and all requested changes
             were made.

       >0    An error occurred.

CONSEQUENCES OF ERRORS         top

       Default.

       The following sections are informative.

APPLICATION USAGE         top

       The interpretation of time is taken to be seconds since the Epoch
       (see the Base Definitions volume of POSIX.1‐2017, Section 4.16,
       Seconds Since the Epoch).  It should be noted that
       implementations conforming to the System Interfaces volume of
       POSIX.1‐2017 do not take leap seconds into account when computing
       seconds since the Epoch. When SS=60 is used, the resulting time
       always refers to 1 plus seconds since the Epoch for a time when
       SS=59.

       Although the -t time option-argument specifies values in 1969,
       the access time and modification time fields are defined in terms
       of seconds since the Epoch (00:00:00 on 1 January 1970 UTC).
       Therefore, depending on the value of TZ when touch is run, there
       is never more than a few valid hours in 1969 and there need not
       be any valid times in 1969.

       If the T time designator is replaced by a <space> for the -d
       date_time option-argument, the <space> must be quoted to prevent
       the shell from splitting the argument.

EXAMPLES         top

       Create or update a file called dwc; the resulting file has both
       the last data modification and last data access timestamps set to
       November 12, 2007 at 10:15:30 local time:

           touch -d 2007-11-12T10:15:30 dwc

       Create or update a file called nick; the resulting file has both
       the last data modification and last data access timestamps set to
       November 12, 2007 at 10:15:30 UTC:

           touch -d 2007-11-12T10:15:30Z nick

       Create or update a file called gwc; the resulting file has both
       the last data modification and last data access timestamps set to
       November 12, 2007 at 10:15:30 local time with a fractional second
       timestamp of .002 seconds:

           touch -d 2007-11-12T10:15:30,002 gwc

       Create or update a file called ajosey; the resulting file has
       both the last data modification and last data access timestamps
       set to November 12, 2007 at 10:15:30 UTC with a fractional second
       timestamp of .002 seconds:

           touch -d "2007-11-12 10:15:30.002Z" ajosey

       Create or update a file called cathy; the resulting file has both
       the last data modification and last data access timestamps set to
       November 12, 2007 at 10:15:00 local time:

           touch -t 200711121015 cathy

       Create or update a file called drepper; the resulting file has
       both the last data modification and last data access timestamps
       set to November 12, 2007 at 10:15:30 local time:

           touch -t 200711121015.30 drepper

       Create or update a file called ebb9; the resulting file has both
       the last data modification and last data access timestamps set to
       November 12, 2007 at 10:15:30 local time:

           touch -t 0711121015.30 ebb9

       Create or update a file called eggert; the resulting file has the
       last data access timestamp set to the corresponding time of the
       file named mark instead of the current time. If the file exists,
       the last data modification time is not changed:

           touch -a -r mark eggert

RATIONALE         top

       The functionality of touch is described almost entirely through
       references to functions in the System Interfaces volume of
       POSIX.1‐2017. In this way, there is no duplication of effort
       required for describing such side-effects as the relationship of
       user IDs to the user database, permissions, and so on.

       There are some significant differences between the touch utility
       in this volume of POSIX.1‐2017 and those in System V and BSD
       systems. They are upwards-compatible for historical applications
       from both implementations:

        1. In System V, an ambiguity exists when a pathname that is a
           decimal number leads the operands; it is treated as a time
           value. In BSD, no time value is allowed; files may only be
           touched to the current time. The -t time construct solves
           these problems for future conforming applications (note that
           the -t option is not historical practice).

        2. The inclusion of the century digits, CC, is also new. Note
           that a ten-digit time value is treated as if YY, and not CC,
           were specified. The caveat about the range of dates following
           the Epoch was included as recognition that some
           implementations are not able to represent dates beyond 18
           January 2038 because they use signed int as a time holder.

       The -r option was added because several comments requested this
       capability.  This option was named -f in an early proposal, but
       was changed because the -f option is used in the BSD version of
       touch with a different meaning.

       At least one historical implementation of touch incremented the
       exit code if -c was specified and the file did not exist. This
       volume of POSIX.1‐2017 requires exit status zero if no errors
       occur.

       In previous version of the standard, if at least two operands are
       specified, and the first operand is an eight or ten-digit decimal
       integer, the first operand was assumed to be a date_time operand.
       This usage was removed in this version of the standard since it
       had been marked obsolescent previously.

       The -d date_time format is an ISO 8601:2004 standard complete
       representation of date and time extended format with an optional
       decimal point or <comma> followed by a string of digits following
       the seconds portion to specify fractions of a second. It is not
       necessary to recognize "[+/-]hh:mm" and "[+/-]hh" to specify
       timezones other than local time and UTC. The T time designator in
       the ISO 8601:2004 standard extended format may be replaced by
       <space>.

FUTURE DIRECTIONS         top

       None.

SEE ALSO         top

       date(1p)

       The Base Definitions volume of POSIX.1‐2017, Section 4.16,
       Seconds Since the Epoch, Chapter 8, Environment Variables,
       Section 12.2, Utility Syntax Guidelines, sys_stat.h(0p)

       The System Interfaces volume of POSIX.1‐2017, creat(3p),
       futimens(3p), time(3p), utime(3p)

COPYRIGHT         top

       Portions of this text are reprinted and reproduced in electronic
       form from IEEE Std 1003.1-2017, Standard for Information
       Technology -- Portable Operating System Interface (POSIX), The
       Open Group Base Specifications Issue 7, 2018 Edition, Copyright
       (C) 2018 by the Institute of Electrical and Electronics
       Engineers, Inc and The Open Group.  In the event of any
       discrepancy between this version and the original IEEE and The
       Open Group Standard, the original IEEE and The Open Group
       Standard is the referee document. The original Standard can be
       obtained online at http://www.opengroup.org/unix/online.html .

       Any typographical or formatting errors that appear in this page
       are most likely to have been introduced during the conversion of
       the source files to man page format. To report such errors, see
       https://www.kernel.org/doc/man-pages/reporting_bugs.html .

IEEE/The Open Group               2017                         TOUCH(1P)

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