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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 <ncurses/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
       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)

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

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