# scr_dump 5 2023-12-30 ncurses 6.4 File formats

    scr_dump(5)                      File formats                      scr_dump(5)

## NAME

           scr_dump - curses screen 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_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:

           o   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
                   #

           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-
               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.

           o   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.

           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 System V, but does not write a  "magic  number"
           to identify the file format.

## PORTABILITY

           There is no standard format for curses screen dumps.  A brief survey of
           the existing implementations follows.

### X/Open Curses

           X/Open Curses, Issue 7 specifies little.  It  says  (boldface  emphasis
           added)

              "[t]he  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 System V systems using older, less capable curses libraries.
           BSD  curses  was  not  relevant  to  X/Open because it did not meet the
           criteria for base-level conformance; see ncurses(3x).

### System V

           System V 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.

           Solaris curses has the following 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).   Solaris curses has no magic number for SVr4 (1989).
           Other System V operating systems (AIX and HP-UX)  use  a  magic  number
           that would correspond to the following.

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

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

               \001\035

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

           Nor do they use an identical format, even  with  the  System V  family.
           The ncurses savescreen test program was used to collect information for
           this manual page.  It produced dumps of different size (all  on  64-bit
           hardware, on 40x80 screens):

           o   AIX (51817 bytes)

           o   HP-UX (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 meet the SVr4 guidelines.  Solaris furthermore supplies two versions
           of curses.

           o   The default curses library uses the SVr3 magic number.

           o   An alternate curses library (which we term xcurses),  available  in
               /usr/xpg4, uses a textual format with no magic number.

               According  to  its  copyright  notice,  this  xcurses  library  was
               developed by MKS (Mortice Kern Systems) from 1990 to 1995.

               Like ncurses6,  it  includes  a  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
           System V and ncurses5, it writes the WINDOW structure  in  binary,  but
           begins  the  file  with  its three-byte identifier "PDC", followed by a
           single-byte version number.

                    "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

           o   the curses shared library major and minor versions as the first two
               bytes (for example, 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.

## EXAMPLES

           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
               ensure 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
               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

## 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)

## SEE ALSO

           curs_scr_dump(3x), curs_util(3x)

    ncurses 6.4                       2023-12-30                       scr_dump(5)