# scr_dump - curses screen dump - man(5) - [phpMan] [_scr_dump_(5)](https://www.chedong.com/phpMan.php/man/scrdump/5/markdown) File formats [_scr_dump_(5)](https://www.chedong.com/phpMan.php/man/scrdump/5/markdown) ## 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: • A “magic number” is written to the beginning of the dump file, allowing applications (such as [**file**(1)](https://www.chedong.com/phpMan.php/man/file/1/markdown)) 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 # • The screen dumps are written in textual form, so that internal data sizes are not di‐ rectly 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 **struc‐ ture, which is much larger than 32-bits. • It is possible to read a screen dump into a terminal with a different screen-size, be‐ cause the library truncates or fills the screen as necessary. • 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 im‐ provements in succeeding years, the basic scheme was unchanged: • The _WINDOW_ structure was written in binary form. • The _WINDOW_ structure refers to lines of data, which were written as an array of binary data following the _WINDOW_. • 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 imple‐ mentations 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 sys‐ tems using older, less capable _curses_ libraries. BSD _curses_ was not relevant to X/Open be‐ cause it did not meet the criteria for base-level conformance; see [**ncurses**(3NCURSES)](https://www.chedong.com/phpMan.php/man/ncurses/3NCURSES/markdown). ### 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). So‐ laris _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-en‐ dian 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)](https://www.chedong.com/phpMan.php/man/od/1/markdown), none of them docu‐ ments 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 dif‐ ferent size (all on 64-bit hardware, on 40x80 screens): • AIX (51817 bytes) • HP-UX (90093 bytes) • Solaris 10 (13273 bytes) • _ncurses_5 (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 fur‐ thermore supplies two versions of _curses._ • The default _curses_ library uses the SVr3 magic number. • An alternate _curses_ library (which we term _xcurses),_ available in _/usr/xpg4,_ uses a tex‐ tual 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 • the _curses_ shared library major and minor versions as the first two bytes (for example, 7 and 1), • followed by a binary dump of the _WINDOW_, • some data for wide characters referenced by the _WINDOW_ structure, and • 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 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)](https://www.chedong.com/phpMan.php/man/COLORPAIR/1/markdown)); move(4, 5); attron(A_BOLD); addstr("Hello"); move(5, 5); attroff(A_BOLD); attrset(A_REVERSE | [COLOR_PAIR(2)](https://www.chedong.com/phpMan.php/man/COLORPAIR/2/markdown)); 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 over‐ looked. • 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 _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 [**scr_dump**(3NCURSES)](https://www.chedong.com/phpMan.php/man/scrdump/3NCURSES/markdown), [**util**(3NCURSES)](https://www.chedong.com/phpMan.php/man/util/3NCURSES/markdown) ncurses 6.4 2023-12-30 [_scr_dump_(5)](https://www.chedong.com/phpMan.php/man/scrdump/5/markdown)