Minix Man Pages

Man Page or Keyword Search:
Man Architecture
Apropos Keyword Search (all sections) Output format
home | help
x minix x
x minixx
scr_dump(5)                   File Formats Manual                  scr_dump(5)

NAME
       scr_dump - format of curses screen-dumps.

SYNOPSIS
       scr_dump

DESCRIPTION
       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_re-
       store 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:

       o   A  "magic number" is written to the beginning of the dump file, al-
           lowing applications (such as  file(1))  to  recognize  curses  dump
           files.

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

               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 pro-
           gram:

               #
               # 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
               #

       o   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-  con-
           figurations.

           The  narrow  library  configuration  holds characters and video at-
           tributes 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.

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

       o   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:

       o   The WINDOW structure was written in binary form.

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

       o   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
       There is no standard format for putwin.  This section gives a brief de-
       scription 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  win-
          dow 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:

          o   Shading is used to identify X/Open Enhanced Curses material, re-
              lating 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 de-
              scribed 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 num-
       ber" 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 infor-
       mation for for this manual page, the savescreen  test-program  produced
       dumps of different size (all on 64-bit hardware, on 40x80 screens):

       o   AIX (51817 bytes)

       o   HPUX (90093 bytes)

       o   Solaris 10 (13273 bytes)

       o   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:

       o   The default curses library uses the SVr3 magic number.

       o   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 writ-
           ing 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_re-
       store (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

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

       o   followed by a binary dump of the WINDOW,

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

       o   finally, lines as done by other implementations.

EXAMPLE
       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:

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

       o   All  characters are shown in printable form; spaces are "\s" to en-
           sure they are not overlooked.

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

       o   The  parameters in the header are written out only if they are non-
           zero.  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  back-
       ground  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
       scr_dump(3NCURSES), util(3NCURSES).

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

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

                                                                   scr_dump(5)

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