1scr_dump(5) File Formats Manual scr_dump(5)
2
6 scr_dump - format of curses screen-dumps.
7
9 scr_dump
10
12 The curses library provides applications with the ability to write the
13 contents of a window to an external file using scr_dump or putwin, and
14 read it back using scr_restore or getwin.
15 The putwin and getwin functions do the work; while scr_dump and
17 scr_restore conveniently save and restore the whole screen, i.e., std‐
18 scr.
19 ncurses6
21 A longstanding implementation of screen-dump was revised with ncurses6
22 to remedy problems with the earlier approach:
23 · A “magic number” is written to the beginning of the dump file,
25 allowing applications (such as file(1)) to recognize curses dump
26 files.
27 Because ncurses6 uses a new format, that requires a new magic num‐
29 ber was unused by other applications. This 16-bit number was
30 unused:
31 0x8888 (octal “\210\210”)
33 but to be more certain, this 32-bit number was chosen:
35 0x88888888 (octal “\210\210\210\210”)
37 This is the pattern submitted to the maintainers of the file pro‐
39 gram:
40 #
42 # ncurses5 (and before) did not use a magic number,
43 # making screen dumps "data".
44 #
45 # ncurses6 (2015) uses this format, ignoring byte-order
46 0 string \210\210\210\210ncurses ncurses6 screen image
47 #
48 · The screen dumps are written in textual form, so that internal data
50 sizes are not directly related to the dump-format, and enabling the
51 library to read dumps from either narrow- or wide-character- con‐
52 figurations.
53 The narrow library configuration holds characters and video
55 attributes in a 32-bit chtype, while the wide-character library
56 stores this information in the cchar_t structure, which is much
57 larger than 32-bits.
58 · It is possible to read a screen dump into a terminal with a differ‐
60 ent screen-size, because the library truncates or fills the screen
61 as necessary.
62 · The ncurses6 getwin reads the legacy screen dumps from ncurses5.
64 ncurses5 (legacy)
66 The screen-dump feature was added to ncurses in June 1995. While there
67 were fixes and improvements in succeeding years, the basic scheme was
68 unchanged:
69 · The WINDOW structure was written in binary form.
71 · The WINDOW structure refers to lines of data, which were written as
73 an array of binary data following the WINDOW.
74 · When getwin restored the window, it would keep track of offsets
76 into the array of line-data and adjust the WINDOW structure which
77 was read back into memory.
78 This is similar to Unix SystemV, but does not write a “magic number” to
80 identify the file format.
81
83 There is no standard format for putwin. This section gives a brief
84 description of the existing formats.
85 X/Open Curses
87 Refer to X/Open Curses, Issue 7 (2009).
88 X/Open's documentation for enhanced curses says only:
90 The getwin( ) function reads window-related data stored in the file
92 by putwin( ). The function then creates and initializes a new win‐
93 dow using that data.
94 The putwin( ) function writes all data associated with win into the
96 stdio stream to which filep points, using an unspecified format.
97 This information can be retrieved later using getwin( ).
98 In the mid-1990s when the X/Open Curses document was written, there
100 were still systems using older, less capable curses libraries (aside
101 from the BSD curses library which was not relevant to X/Open because it
102 did not meet the criteria for base curses). The document explained the
103 term “enhanced” as follows:
104 · Shading is used to identify X/Open Enhanced Curses material,
106 relating to interfaces included to provide enhanced capabilities
107 for applications originally written to be compiled on systems
108 based on the UNIX operating system. Therefore, the features
109 described may not be present on systems that conform to XPG4 or
110 to earlier XPG releases. The relevant reference pages may pro‐
111 vide additional or more specific portability warnings about use
112 of the material.
113 In the foregoing, emphasis was added to unspecified format and to XPG4
115 or to earlier XPG releases, for clarity.
116 Unix SystemV
118 Unix SystemV curses identified the file format by writing a “magic num‐
119 ber” at the beginning of the dump. The WINDOW data and the lines of
120 text follow, all in binary form.
121 The Solaris curses source has these definitions:
123 /* terminfo magic number */
125 #define MAGNUM 0432
126 /* curses screen dump magic number */
128 #define SVR2_DUMP_MAGIC_NUMBER 0433
129 #define SVR3_DUMP_MAGIC_NUMBER 0434
130 That is, the feature was likely introduced in SVr2 (1984), and improved
132 in SVr3 (1987). The Solaris curses source has no magic number for SVr4
133 (1989). Other operating systems (AIX and HPUX) use a magic number
134 which would correspond to this definition:
135 /* curses screen dump magic number */
137 #define SVR4_DUMP_MAGIC_NUMBER 0435
138 That octal number in bytes is 001, 035. Because most Unix vendors use
140 big-endian hardware, the magic number is written with the high-order
141 byte first, e.g.,
142 01 35
144 After the magic number, the WINDOW structure and line-data are written
146 in binary format. While the magic number used by the Unix systems can
147 be seen using od(1), none of the Unix systems documents the format used
148 for screen-dumps.
149 The Unix systems do not use identical formats. While collecting infor‐
151 mation for for this manual page, the savescreen test-program produced
152 dumps of different size (all on 64-bit hardware, on 40x80 screens):
153 · AIX (51817 bytes)
155 · HPUX (90093 bytes)
157 · Solaris 10 (13273 bytes)
159 · ncurses5 (12888 bytes)
161 Solaris
163 As noted above, Solaris curses has no magic number corresponding to
164 SVr4 curses. This is odd since Solaris was the first operating system
165 to pass the SVr4 guidelines. Solaris has two versions of curses:
166 · The default curses library uses the SVr3 magic number.
168 · There is an alternate curses library in /usr/xpg4. This uses a
170 textual format with no magic number.
171 According to the copyright notice, the xpg4 Solaris curses library
173 was developed by MKS (Mortice Kern Systems) from 1990 to 1995.
174 Like ncurses6, there is a file-header with parameters. Unlike
176 ncurses6, the contents of the window are written piecemeal, with
177 coordinates and attributes for each chunk of text rather than writ‐
178 ing the whole window from top to bottom.
179 PDCurses
181 PDCurses added support for screen dumps in version 2.7 (2005). Like
182 Unix SystemV and ncurses5, it writes the WINDOW structure in binary,
183 but begins the file with its three-byte identifier “PDC”, followed by a
184 one-byte version, e.g.,
185 “PDC\001”
187 NetBSD
189 As of April 2017, NetBSD curses does not support scr_dump and
190 scr_restore (or scr_init, scr_set), although it has putwin and getwin.
191 Like ncurses5, NetBSD putwin does not identify its dumps with a useful
193 magic number. It writes
194 · the curses shared library major and minor versions as the first two
196 bytes (e.g., 7 and 1),
197 · followed by a binary dump of the WINDOW,
199 · some data for wide-characters referenced by the WINDOW structure,
201 and
202 · finally, lines as done by other implementations.
204
206 Given a simple program which writes text to the screen (and for the
207 sake of example, limiting the screen-size to 10x20):
208 #include <curses.h>
210 int
212 main(void)
213 {
214 putenv("LINES=10");
215 putenv("COLUMNS=20");
216 initscr();
217 start_color();
218 init_pair(1, COLOR_WHITE, COLOR_BLUE);
219 init_pair(2, COLOR_RED, COLOR_BLACK);
220 bkgd(COLOR_PAIR(1));
221 move(4, 5);
222 attron(A_BOLD);
223 addstr("Hello");
224 move(5, 5);
225 attroff(A_BOLD);
226 attrset(A_REVERSE | COLOR_PAIR(2));
227 addstr("World!");
228 refresh();
229 scr_dump("foo.out");
230 endwin();
231 return 0;
232 }
233 When run using ncurses6, the output looks like this:
235 \210\210\210\210ncurses 6.0.20170415
237 _cury=5
238 _curx=11
239 _maxy=9
240 _maxx=19
241 _flags=14
242 _attrs=\{REVERSE|C2}
243 flag=_idcok
244 _delay=-1
245 _regbottom=9
246 _bkgrnd=\{NORMAL|C1}\s
247 rows:
248 1:\{NORMAL|C1}\s\s\s\s\s\s\s\s\s\s\s\s\s\s\s\s\s\s\s\s
249 2:\s\s\s\s\s\s\s\s\s\s\s\s\s\s\s\s\s\s\s\s
250 3:\s\s\s\s\s\s\s\s\s\s\s\s\s\s\s\s\s\s\s\s
251 4:\s\s\s\s\s\s\s\s\s\s\s\s\s\s\s\s\s\s\s\s
252 5:\s\s\s\s\s\{BOLD}Hello\{NORMAL}\s\s\s\s\s\s\s\s\s\s
253 6:\s\s\s\s\s\{REVERSE|C2}World!\{NORMAL|C1}\s\s\s\s\s\s\s\s\s
254 7:\s\s\s\s\s\s\s\s\s\s\s\s\s\s\s\s\s\s\s\s
255 8:\s\s\s\s\s\s\s\s\s\s\s\s\s\s\s\s\s\s\s\s
256 9:\s\s\s\s\s\s\s\s\s\s\s\s\s\s\s\s\s\s\s\s
257 10:\s\s\s\s\s\s\s\s\s\s\s\s\s\s\s\s\s\s\s\s
258 The first four octal escapes are actually nonprinting characters, while
260 the remainder of the file is printable text. You may notice:
261 · The actual color pair values are not written to the file.
263 · All characters are shown in printable form; spaces are “\s” to
265 ensure they are not overlooked.
266 · Attributes are written in escaped curly braces, e.g., “\{BOLD}”,
268 and may include a color-pair (C1 or C2 in this example).
269 · The parameters in the header are written out only if they are
271 nonzero. When reading back, order does not matter.
272 Running the same program with Solaris xpg4 curses gives this dump:
274 MAX=10,20
276 BEG=0,0
277 SCROLL=0,10
278 VMIN=1
279 VTIME=0
280 FLAGS=0x1000
281 FG=0,0
282 BG=0,0,
283 0,0,0,1,
284 0,19,0,0,
285 1,0,0,1,
286 1,19,0,0,
287 2,0,0,1,
288 2,19,0,0,
289 3,0,0,1,
290 3,19,0,0,
291 4,0,0,1,
292 4,5,0x20,0,Hello
293 4,10,0,1,
294 4,19,0,0,
295 5,0,0,1,
296 5,5,0x4,2,World!
297 5,11,0,1,
298 5,19,0,0,
299 6,0,0,1,
300 6,19,0,0,
301 7,0,0,1,
302 7,19,0,0,
303 8,0,0,1,
304 8,19,0,0,
305 9,0,0,1,
306 9,19,0,0,
307 CUR=11,5
308 Solaris getwin requires that all parameters are present, and in the
310 same order. The xpg4 curses library does not know about the bce (back
311 color erase) capability, and does not color the window background.
312 On the other hand, the SVr4 curses library does know about the back‐
314 ground color. However, its screen dumps are in binary. Here is the
315 corresponding dump (using “od -t x1”):
316 0000000 1c 01 c3 d6 f3 58 05 00 0b 00 0a 00 14 00 00 00
318 0000020 00 00 02 00 00 00 00 00 00 00 00 00 00 00 00 00
319 0000040 00 00 b8 1a 06 08 cc 1a 06 08 00 00 09 00 10 00
320 0000060 00 00 00 80 00 00 20 00 00 00 ff ff ff ff 00 00
321 0000100 ff ff ff ff 00 00 00 00 20 80 00 00 20 80 00 00
322 0000120 20 80 00 00 20 80 00 00 20 80 00 00 20 80 00 00
323 *
324 0000620 20 80 00 00 20 80 00 00 20 80 00 00 48 80 00 04
325 0000640 65 80 00 04 6c 80 00 04 6c 80 00 04 6f 80 00 04
326 0000660 20 80 00 00 20 80 00 00 20 80 00 00 20 80 00 00
327 *
328 0000740 20 80 00 00 20 80 00 00 20 80 00 00 57 00 81 00
329 0000760 6f 00 81 00 72 00 81 00 6c 00 81 00 64 00 81 00
330 0001000 21 00 81 00 20 80 00 00 20 80 00 00 20 80 00 00
331 0001020 20 80 00 00 20 80 00 00 20 80 00 00 20 80 00 00
332 *
333 0001540 20 80 00 00 20 80 00 00 00 00 f6 d1 01 00 f6 d1
334 0001560 08 00 00 00 40 00 00 00 00 00 00 00 00 00 00 07
335 0001600 00 04 00 01 00 01 00 00 00 01 00 00 00 00 00 00
336 0001620 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
337 *
338 0002371
339
341 curs_scr_dump(3X), curs_util(3X).
342
344 Thomas E. Dickey
345 extended screen-dump format for ncurses 6.0 (2015)
346 Eric S. Raymond
348 screen dump feature in ncurses 1.9.2d (1995)
349 scr_dump(5)