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scr_dump 5

scr_dump(5)                                                        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.,  std-
       scr.


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  num-
           ber  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  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
           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 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
       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 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,
              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 pro-
              vide 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_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 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

       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)