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scr_dump 5

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_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 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
       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:

          o   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):

       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
           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

       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
           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


SEE ALSO

       curs_scr_dump(3x), curs_util(3x).


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)