scr_dump(5) — Linux manual page

NAME | SYNOPSIS | DESCRIPTION | PORTABILITY | EXAMPLE | SEE ALSO | AUTHORS | COLOPHON

scr_dump(5)                File Formats Manual               scr_dump(5)

NAME         top

       scr_dump - format of curses screen-dumps.

SYNOPSIS         top

       scr_dump

DESCRIPTION         top

       The curses library provides applications with the ability to
       write the contents of a window to an external file using scr_dump
       or putwin, and read it back using scr_restore or getwin.

       The putwin and getwin functions do the work; while scr_dump and
       scr_restore conveniently save and restore the whole screen, i.e.,
       stdscr.

   ncurses6
       A longstanding implementation of screen-dump was revised with
       ncurses6 to remedy problems with the earlier approach:

       •   A “magic number” is written to the beginning of the dump
           file, allowing applications (such as file(1)) to recognize
           curses dump files.

           Because ncurses6 uses a new format, that requires a new magic
           number was unused by other applications.  This 16-bit number
           was unused:

               0x8888 (octal “\210\210”)

           but to be more certain, this 32-bit number was chosen:

               0x88888888 (octal “\210\210\210\210”)

           This is the pattern submitted to the maintainers of the file
           program:

               #
               # ncurses5 (and before) did not use a magic number,
               # making screen dumps "data".
               #
               # ncurses6 (2015) uses this format, ignoring byte-order
               0    string    \210\210\210\210ncurses    ncurses6 screen image
               #

       •   The screen dumps are written in textual form, so that
           internal data sizes are not directly related to the dump-
           format, and enabling the library to read dumps from either
           narrow- or wide-character- configurations.

           The narrow library configuration holds characters and video
           attributes in a 32-bit chtype, while the wide-character
           library stores this information in the cchar_t structure,
           which is much larger than 32-bits.

       •   It is possible to read a screen dump into a terminal with a
           different screen-size, because the library truncates or fills
           the screen as necessary.

       •   The ncurses6 getwin reads the legacy screen dumps from
           ncurses5.

   ncurses5 (legacy)
       The screen-dump feature was added to ncurses in June 1995.  While
       there were fixes and improvements in succeeding years, the basic
       scheme was unchanged:

       •   The WINDOW structure was written in binary form.

       •   The WINDOW structure refers to lines of data, which were
           written as an array of binary data following the WINDOW.

       •   When getwin restored the window, it would keep track of
           offsets into the array of line-data and adjust the WINDOW
           structure which was read back into memory.

       This is similar to Unix SystemV, but does not write a “magic
       number” to identify the file format.

PORTABILITY         top

       There is no standard format for putwin.  This section gives a
       brief description of the existing formats.

   X/Open Curses
       Refer to X/Open Curses, Issue 7 (2009).

       X/Open's documentation for enhanced curses says only:

          The getwin( ) function reads window-related data stored in the
          file by putwin( ).  The function then creates and initializes
          a new window using that data.

          The putwin( ) function writes all data associated with win
          into the stdio stream to which filep points, using an
          unspecified format.  This information can be retrieved later
          using getwin( ).

       In the mid-1990s when the X/Open Curses document was written,
       there were still systems using older, less capable curses
       libraries (aside from the BSD curses library which was not
       relevant to X/Open because it did not meet the criteria for base
       curses).  The document explained the term “enhanced” as follows:

          •   Shading is used to identify X/Open Enhanced Curses
              material, relating to interfaces included to provide
              enhanced capabilities for applications originally written
              to be compiled on systems based on the UNIX operating
              system.  Therefore, the features described may not be
              present on systems that conform to XPG4 or to earlier XPG
              releases.  The relevant reference pages may provide
              additional or more specific portability warnings about use
              of the material.

       In the foregoing, emphasis was added to unspecified format and to
       XPG4 or to earlier XPG releases, for clarity.

   Unix SystemV
       Unix SystemV curses identified the file format by writing a
       “magic number” at the beginning of the dump.  The WINDOW data and
       the lines of text follow, all in binary form.

       The Solaris curses source has these definitions:

           /* terminfo magic number */
           #define MAGNUM  0432

           /* curses screen dump magic number */
           #define SVR2_DUMP_MAGIC_NUMBER  0433
           #define SVR3_DUMP_MAGIC_NUMBER  0434

       That is, the feature was likely introduced in SVr2 (1984), and
       improved in SVr3 (1987).  The Solaris curses source has no magic
       number for SVr4 (1989).  Other operating systems (AIX and HPUX)
       use a magic number which would correspond to this definition:

           /* curses screen dump magic number */
           #define SVR4_DUMP_MAGIC_NUMBER  0435

       That octal number in bytes is 001, 035.  Because most Unix
       vendors use big-endian hardware, the magic number is written with
       the high-order byte first, e.g.,

            01 35

       After the magic number, the WINDOW structure and line-data are
       written in binary format.  While the magic number used by the
       Unix systems can be seen using od(1), none of the Unix systems
       documents the format used for screen-dumps.

       The Unix systems do not use identical formats.  While collecting
       information for for this manual page, the savescreen test-program
       produced dumps of different size (all on 64-bit hardware, on
       40x80 screens):

       •   AIX (51817 bytes)

       •   HPUX (90093 bytes)

       •   Solaris 10 (13273 bytes)

       •   ncurses5 (12888 bytes)

   Solaris
       As noted above, Solaris curses has no magic number corresponding
       to SVr4 curses.  This is odd since Solaris was the first
       operating system to pass the SVr4 guidelines.  Solaris has two
       versions of curses:

       •   The default curses library uses the SVr3 magic number.

       •   There is an alternate curses library in /usr/xpg4.  This uses
           a textual format with no magic number.

           According to the copyright notice, the xpg4 Solaris curses
           library was developed by MKS (Mortice Kern Systems) from 1990
           to 1995.

           Like ncurses6, there is a file-header with parameters.
           Unlike ncurses6, the contents of the window are written
           piecemeal, with coordinates and attributes for each chunk of
           text rather than writing the whole window from top to bottom.

   PDCurses
       PDCurses added support for screen dumps in version 2.7 (2005).
       Like Unix SystemV and ncurses5, it writes the WINDOW structure in
       binary, but begins the file with its three-byte identifier “PDC”,
       followed by a one-byte version, e.g.,

                “PDC\001”

   NetBSD
       As of April 2017, NetBSD curses does not support scr_dump and
       scr_restore (or scr_init, scr_set), although it has putwin and
       getwin.

       Like ncurses5, NetBSD putwin does not identify its dumps with a
       useful magic number.  It writes

       •   the curses shared library major and minor versions as the
           first two bytes (e.g., 7 and 1),

       •   followed by a binary dump of the WINDOW,

       •   some data for wide-characters referenced by the WINDOW
           structure, and

       •   finally, lines as done by other implementations.

EXAMPLE         top

       Given a simple program which writes text to the screen (and for
       the sake of example, limiting the screen-size to 10x20):

           #include <curses.h>

           int
           main(void)
           {
               putenv("LINES=10");
               putenv("COLUMNS=20");
               initscr();
               start_color();
               init_pair(1, COLOR_WHITE, COLOR_BLUE);
               init_pair(2, COLOR_RED, COLOR_BLACK);
               bkgd(COLOR_PAIR(1));
               move(4, 5);
               attron(A_BOLD);
               addstr("Hello");
               move(5, 5);
               attroff(A_BOLD);
               attrset(A_REVERSE | COLOR_PAIR(2));
               addstr("World!");
               refresh();
               scr_dump("foo.out");
               endwin();
               return 0;
           }

       When run using ncurses6, the output looks like this:

           \210\210\210\210ncurses 6.0.20170415
           _cury=5
           _curx=11
           _maxy=9
           _maxx=19
           _flags=14
           _attrs=\{REVERSE|C2}
           flag=_idcok
           _delay=-1
           _regbottom=9
           _bkgrnd=\{NORMAL|C1}\s
           rows:
           1:\{NORMAL|C1}\s\s\s\s\s\s\s\s\s\s\s\s\s\s\s\s\s\s\s\s
           2:\s\s\s\s\s\s\s\s\s\s\s\s\s\s\s\s\s\s\s\s
           3:\s\s\s\s\s\s\s\s\s\s\s\s\s\s\s\s\s\s\s\s
           4:\s\s\s\s\s\s\s\s\s\s\s\s\s\s\s\s\s\s\s\s
           5:\s\s\s\s\s\{BOLD}Hello\{NORMAL}\s\s\s\s\s\s\s\s\s\s
           6:\s\s\s\s\s\{REVERSE|C2}World!\{NORMAL|C1}\s\s\s\s\s\s\s\s\s
           7:\s\s\s\s\s\s\s\s\s\s\s\s\s\s\s\s\s\s\s\s
           8:\s\s\s\s\s\s\s\s\s\s\s\s\s\s\s\s\s\s\s\s
           9:\s\s\s\s\s\s\s\s\s\s\s\s\s\s\s\s\s\s\s\s
           10:\s\s\s\s\s\s\s\s\s\s\s\s\s\s\s\s\s\s\s\s

       The first four octal escapes are actually nonprinting characters,
       while the remainder of the file is printable text.  You may
       notice:

       •   The actual color pair values are not written to the file.

       •   All characters are shown in printable form; spaces are “\s”
           to ensure they are not overlooked.

       •   Attributes are written in escaped curly braces, e.g.,
           “\{BOLD}”, and may include a color-pair (C1 or C2 in this
           example).

       •   The parameters in the header are written out only if they are
           nonzero.  When reading back, order does not matter.

       Running the same program with Solaris xpg4 curses gives this
       dump:

           MAX=10,20
           BEG=0,0
           SCROLL=0,10
           VMIN=1
           VTIME=0
           FLAGS=0x1000
           FG=0,0
           BG=0,0,
           0,0,0,1,
           0,19,0,0,
           1,0,0,1,
           1,19,0,0,
           2,0,0,1,
           2,19,0,0,
           3,0,0,1,
           3,19,0,0,
           4,0,0,1,
           4,5,0x20,0,Hello
           4,10,0,1,
           4,19,0,0,
           5,0,0,1,
           5,5,0x4,2,World!
           5,11,0,1,
           5,19,0,0,
           6,0,0,1,
           6,19,0,0,
           7,0,0,1,
           7,19,0,0,
           8,0,0,1,
           8,19,0,0,
           9,0,0,1,
           9,19,0,0,
           CUR=11,5

       Solaris getwin requires that all parameters are present, and in
       the same order.  The xpg4 curses library does not know about the
       bce (back color erase) capability, and does not color the window
       background.

       On the other hand, the SVr4 curses library does know about the
       background color.  However, its screen dumps are in binary.  Here
       is the corresponding dump (using “od -t x1”):

           0000000 1c 01 c3 d6 f3 58 05 00 0b 00 0a 00 14 00 00 00
           0000020 00 00 02 00 00 00 00 00 00 00 00 00 00 00 00 00
           0000040 00 00 b8 1a 06 08 cc 1a 06 08 00 00 09 00 10 00
           0000060 00 00 00 80 00 00 20 00 00 00 ff ff ff ff 00 00
           0000100 ff ff ff ff 00 00 00 00 20 80 00 00 20 80 00 00
           0000120 20 80 00 00 20 80 00 00 20 80 00 00 20 80 00 00
           *
           0000620 20 80 00 00 20 80 00 00 20 80 00 00 48 80 00 04
           0000640 65 80 00 04 6c 80 00 04 6c 80 00 04 6f 80 00 04
           0000660 20 80 00 00 20 80 00 00 20 80 00 00 20 80 00 00
           *
           0000740 20 80 00 00 20 80 00 00 20 80 00 00 57 00 81 00
           0000760 6f 00 81 00 72 00 81 00 6c 00 81 00 64 00 81 00
           0001000 21 00 81 00 20 80 00 00 20 80 00 00 20 80 00 00
           0001020 20 80 00 00 20 80 00 00 20 80 00 00 20 80 00 00
           *
           0001540 20 80 00 00 20 80 00 00 00 00 f6 d1 01 00 f6 d1
           0001560 08 00 00 00 40 00 00 00 00 00 00 00 00 00 00 07
           0001600 00 04 00 01 00 01 00 00 00 01 00 00 00 00 00 00
           0001620 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
           *
           0002371

SEE ALSO         top

       curs_scr_dump(3X), curs_util(3X).

AUTHORS         top

       Thomas E. Dickey
       extended screen-dump format for ncurses 6.0 (2015)

       Eric S. Raymond
       screen dump feature in ncurses 1.9.2d (1995)

COLOPHON         top

       This page is part of the ncurses (new curses) project.
       Information about the project can be found at 
       ⟨https://www.gnu.org/software/ncurses/ncurses.html⟩.  If you have
       a bug report for this manual page, send it to
       bug-ncurses-request@gnu.org.  This page was obtained from the
       project's upstream Git mirror of the CVS repository
       ⟨git://ncurses.scripts.mit.edu/ncurses.git⟩ on 2021-08-27.  (At
       that time, the date of the most recent commit that was found in
       the repository was 2021-05-23.)  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

                                                             scr_dump(5)

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