scr_dump(5) File formats scr_dump(5) #
scr_dump(5) File formats scr_dump(5)
NNAAMMEE #
scr_dump - format of curses screen-dumps.
SSYYNNOOPPSSIISS #
ssccrr__dduummpp
DDEESSCCRRIIPPTTIIOONN #
The curses library provides applications with the ability to write the
contents of a window to an external file using ssccrr__dduummpp or ppuuttwwiinn, and
read it back using ssccrr__rreessttoorree or ggeettwwiinn.
The ppuuttwwiinn and ggeettwwiinn functions do the work; while ssccrr__dduummpp and
ssccrr__rreessttoorree conveniently save and restore the whole screen, i.e., ssttddssccrr.
nnccuurrsseess66 A longstanding implementation of screen-dump was revised with ncurses6 to remedy problems with the earlier approach:
• A “magic number” is written to the beginning of the dump file,
allowing applications (such as ffiillee(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 ffiillee 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
#
• 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 _n_a_r_r_o_w library configuration holds characters and video
attributes in a 32-bit cchhttyyppee, while the _w_i_d_e_-_c_h_a_r_a_c_t_e_r library
stores this information in the cccchhaarr__tt structure, which is much
larger than 32-bits.
• 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.
• The ncurses6 ggeettwwiinn reads the legacy screen dumps from ncurses5.
nnccuurrsseess55 ((lleeggaaccyy)) 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:
• The WWIINNDDOOWW structure was written in binary form.
• The WWIINNDDOOWW structure refers to lines of data, which were written as
an array of binary data following the WWIINNDDOOWW.
• When ggeettwwiinn restored the window, it would keep track of offsets into
the array of line-data and adjust the WWIINNDDOOWW 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.
PPOORRTTAABBIILLIITTYY #
There is no standard format for ppuuttwwiinn. This section gives a brief
description of the existing formats.
XX//OOppeenn CCuurrsseess Refer to _X_/_O_p_e_n _C_u_r_s_e_s_, _I_s_s_u_e _7 (2009).
X/Open's documentation for _e_n_h_a_n_c_e_d _c_u_r_s_e_s says only:
The ggeettwwiinn(( )) function reads window-related data stored in the file by
_p_u_t_w_i_n_(_ _). The function then creates and initializes a new window
using that data.
The ppuuttwwiinn(( )) function writes all data associated with _w_i_n into the
ssttddiioo(3) stream to which _f_i_l_e_p points, using an uunnssppeecciiffiieedd ffoorrmmaatt.
This information can be retrieved later using ggeettwwiinn(( )).
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 _b_a_s_e _c_u_r_s_e_s). The document explained the term
“enhanced” as follows:
• Shading is used to identify _X_/_O_p_e_n _E_n_h_a_n_c_e_d _C_u_r_s_e_s 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 XXPPGG44 oorr ttoo
eeaarrlliieerr XXPPGG rreelleeaasseess. The relevant reference pages may provide
additional or more specific portability warnings about use of the
material.
In the foregoing, emphasis was added to uunnssppeecciiffiieedd ffoorrmmaatt and to XXPPGG44 oorr
ttoo eeaarrlliieerr XXPPGG rreelleeaasseess, for clarity.
UUnniixx SSyysstteemmVV Unix SystemV curses identified the file format by writing a “magic number” at the beginning of the dump. The WWIINNDDOOWW 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 WWIINNDDOOWW structure and line-data are written in
binary format. While the magic number used by the Unix systems can be
seen using oodd(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 _s_a_v_e_s_c_r_e_e_n test-program
produced dumps of different size (all on 64-bit hardware, on 40x80
screens):
• AIX (51817 bytes)
• HPUX (90093 bytes)
• Solaris 10 (13273 bytes)
• ncurses5 (12888 bytes)
SSoollaarriiss 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:
• The default curses library uses the SVr3 magic number.
• There is an alternate curses library in //uussrr//xxppgg44. This uses a
textual format with no magic number.
According to the copyright notice, the _x_p_g_4 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.
PPDDCCuurrsseess PDCurses added support for screen dumps in version 2.7 (2005). Like Unix SystemV and ncurses5, it writes the WWIINNDDOOWW structure in binary, but begins the file with its three-byte identifier “PDC”, followed by a one- byte version, e.g.,
“PDC\001” #
NNeettBBSSDD As of April 2017, NetBSD curses does not support ssccrr__dduummpp and ssccrr__rreessttoorree (or ssccrr__iinniitt, ssccrr__sseett), although it has ppuuttwwiinn and ggeettwwiinn.
Like ncurses5, NetBSD ppuuttwwiinn does not identify its dumps with a useful
magic number. It writes
• the curses shared library major and minor versions as the first two
bytes (e.g., 7 and 1),
• followed by a binary dump of the WWIINNDDOOWW,
• some data for wide-characters referenced by the WWIINNDDOOWW structure, and
• finally, lines as done by other implementations.
EEXXAAMMPPLLEE #
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:
• The actual color pair values are not written to the file.
• All characters are shown in printable form; spaces are “\s” to ensure
they are not overlooked.
• Attributes are written in escaped curly braces, e.g., “\{BOLD}”, and
may include a color-pair (C1 or C2 in this example).
• 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 _x_p_g_4 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 ggeettwwiinn requires that all parameters are present, and in the same
order. The _x_p_g_4 curses library does not know about the bbccee (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
SSEEEE AALLSSOO #
ccuurrss__ssccrr__dduummpp(3), ccuurrss__uuttiill(3).
AAUUTTHHOORRSS #
Thomas E. Dickey
extended screen-dump format for ncurses 6.0 (2015)
Eric S. Raymond
screen dump feature in ncurses 1.9.2d (1995)
ncurses 6.4 2023-07-01 scr_dump(5)