1TOUCH(1P) POSIX Programmer's Manual TOUCH(1P)
2
6 This manual page is part of the POSIX Programmer's Manual. The Linux
7 implementation of this interface may differ (consult the corresponding
8 Linux manual page for details of Linux behavior), or the interface may
9 not be implemented on Linux.
10
13 touch — change file access and modification times
14
16 touch [−acm] [−r ref_file|−t time|−d date_time] file...
17
19 The touch utility shall change the last data modification timestamps,
20 the last data access timestamps, or both.
21 The time used can be specified by the −t time option-argument, the cor‐
23 responding time fields of the file referenced by the −r ref_file
24 option-argument, or the −d date_time option-argument, as specified in
25 the following sections. If none of these are specified, touch shall use
26 the current time.
27 For each file operand, touch shall perform actions equivalent to the
29 following functions defined in the System Interfaces volume of
30 POSIX.1‐2008:
31 1. If file does not exist:
33 a. The creat() function is called with the following arguments:
35 -- The file operand is used as the path argument.
37 -- The value of the bitwise-inclusive OR of S_IRUSR, S_IWUSR,
39 S_IRGRP, S_IWGRP, S_IROTH, and S_IWOTH is used as the mode
40 argument.
41 b. The futimens() function is called with the following arguments:
43 -- The file descriptor opened in step 1a.
45 -- The access time and the modification time, set as described
47 in the OPTIONS section, are used as the first and second
48 elements of the times array argument, respectively.
49 2. If file exists, the utimensat() function is called with the follow‐
51 ing arguments:
52 a. The AT_FDCWD special value is used as the fd argument.
54 b. The file operand is used as the path argument.
56 c. The access time and the modification time, set as described in
58 the OPTIONS section, are used as the first and second elements
59 of the times array argument, respectively.
60 d. The flag argument is set to zero.
62
64 The touch utility shall conform to the Base Definitions volume of
65 POSIX.1‐2008, Section 12.2, Utility Syntax Guidelines.
66 The following options shall be supported:
68 −a Change the access time of file. Do not change the modifica‐
70 tion time unless −m is also specified.
71 −c Do not create a specified file if it does not exist. Do not
73 write any diagnostic messages concerning this condition.
74 −d date_time
76 Use the specified date_time instead of the current time. The
77 option-argument shall be a string of the form:
78 YYYY−MM−DDThh:mm:SS[.frac][tz]
80 or:
82 YYYY−MM−DDThh:mm:SS[,frac][tz]
84 where:
86 * YYYY are at least four decimal digits giving the year.
88 * MM, DD, hh, mm, and SS are as with −t time.
90 * T is the time designator, and can be replaced by a single
92 <space>.
93 * [.frac] and [,frac] are either empty, or a <period> ('.')
95 or a <comma> (',') respectively, followed by one or more
96 decimal digits, specifying a fractional second.
97 * [tz] is either empty, signifying local time, or the let‐
99 ter 'Z', signifying UTC. If [tz] is empty, the resulting
100 time shall be affected by the value of the TZ environment
101 variable.
102 If the resulting time precedes the Epoch, the behavior is
104 implementation-defined. If the time cannot be represented as
105 the file's timestamp, touch shall exit immediately with an
106 error status.
107 −m Change the modification time of file. Do not change the
109 access time unless −a is also specified.
110 −r ref_file
112 Use the corresponding time of the file named by the pathname
113 ref_file instead of the current time.
114 −t time Use the specified time instead of the current time. The
116 option-argument shall be a decimal number of the form:
117 [[CC]YY]MMDDhhmm[.SS]
119 where each two digits represents the following:
121 MM The month of the year [01,12].
123 DD The day of the month [01,31].
125 hh The hour of the day [00,23].
127 mm The minute of the hour [00,59].
129 CC The first two digits of the year (the century).
131 YY The second two digits of the year.
133 SS The second of the minute [00,60].
135 Both CC and YY shall be optional. If neither is given, the
137 current year shall be assumed. If YY is specified, but CC is
138 not, CC shall be derived as follows:
139 ┌──────────┬─────────────┐
141 │If YY is: │ CC becomes: │
142 ├──────────┼─────────────┤
143 │ [69,99] │ 19 │
144 │ [00,68] │ 20 │
145 └──────────┴─────────────┘
146 Note: It is expected that in a future version of this
147 standard the default century inferred from a
148 2-digit year will change. (This would apply to all
149 commands accepting a 2-digit year as input.)
150 The resulting time shall be affected by the value of the TZ
152 environment variable. If the resulting time value precedes
153 the Epoch, the behavior is implementation-defined. If the
154 time is out of range for the file's timestamp, touch shall
155 exit immediately with an error status. The range of valid
156 times past the Epoch is implementation-defined, but it shall
157 extend to at least the time 0 hours, 0 minutes, 0 seconds,
158 January 1, 2038, Coordinated Universal Time. Some implementa‐
159 tions may not be able to represent dates beyond January 18,
160 2038, because they use signed int as a time holder.
161 The range for SS is [00,60] rather than [00,59] because of
163 leap seconds. If SS is 60, and the resulting time, as
164 affected by the TZ environment variable, does not refer to a
165 leap second, the resulting time shall be one second after a
166 time where SS is 59. If SS is not given a value, it is
167 assumed to be zero.
168 If neither the −a nor −m options were specified, touch shall behave as
170 if both the −a and −m options were specified.
171
173 The following operands shall be supported:
174 file A pathname of a file whose times shall be modified.
176
178 Not used.
179
181 None.
182
184 The following environment variables shall affect the execution of
185 touch:
186 LANG Provide a default value for the internationalization vari‐
188 ables that are unset or null. (See the Base Definitions vol‐
189 ume of POSIX.1‐2008, Section 8.2, Internationalization Vari‐
190 ables for the precedence of internationalization variables
191 used to determine the values of locale categories.)
192 LC_ALL If set to a non-empty string value, override the values of
194 all the other internationalization variables.
195 LC_CTYPE Determine the locale for the interpretation of sequences of
197 bytes of text data as characters (for example, single-byte as
198 opposed to multi-byte characters in arguments).
199 LC_MESSAGES
201 Determine the locale that should be used to affect the format
202 and contents of diagnostic messages written to standard
203 error.
204 NLSPATH Determine the location of message catalogs for the processing
206 of LC_MESSAGES.
207 TZ Determine the timezone to be used for interpreting the time
209 option-argument. If TZ is unset or null, an unspecified
210 default timezone shall be used.
211
213 Default.
214
216 Not used.
217
219 The standard error shall be used only for diagnostic messages.
220
222 None.
223
225 None.
226
228 The following exit values shall be returned:
229 0 The utility executed successfully and all requested changes were
231 made.
232 >0 An error occurred.
234
236 Default.
237 The following sections are informative.
239
241 The interpretation of time is taken to be seconds since the Epoch (see
242 the Base Definitions volume of POSIX.1‐2008, Section 4.15, Seconds
243 Since the Epoch). It should be noted that implementations conforming
244 to the System Interfaces volume of POSIX.1‐2008 do not take leap sec‐
245 onds into account when computing seconds since the Epoch. When SS=60 is
246 used, the resulting time always refers to 1 plus seconds since the
247 Epoch for a time when SS=59.
248 Although the −t time option-argument specifies values in 1969, the
250 access time and modification time fields are defined in terms of sec‐
251 onds since the Epoch (00:00:00 on 1 January 1970 UTC). Therefore,
252 depending on the value of TZ when touch is run, there is never more
253 than a few valid hours in 1969 and there need not be any valid times in
254 1969.
255 One ambiguous situation occurs if −t time is not specified, −r ref_file
257 is not specified, and the first operand is an eight or ten-digit deci‐
258 mal number. A portable script can avoid this problem by using:
259 touch −− file
261 or:
263 touch ./file
265 in this case.
267 If the T time designator is replaced by a <space> for the −d date_time
269 option-argument, the <space> must be quoted to prevent the shell from
270 splitting the argument.
271
273 Create or update a file called dwc; the resulting file has both the
274 last data modification and last data access timestamps set to November
275 12, 2007 at 10:15:30 local time:
276 touch −d 2007-11-12T10:15:30 dwc
278 Create or update a file called nick; the resulting file has both the
280 last data modification and last data access timestamps set to November
281 12, 2007 at 10:15:30 UTC:
282 touch −d 2007-11-12T10:15:30Z nick
284 Create or update a file called gwc; the resulting file has both the
286 last data modification and last data access timestamps set to November
287 12, 2007 at 10:15:30 local time with a fractional second timestamp of
288 .002 seconds:
289 touch −d 2007-11-12T10:15:30,002 gwc
291 Create or update a file called ajosey; the resulting file has both the
293 last data modification and last data access timestamps set to November
294 12, 2007 at 10:15:30 UTC with a fractional second timestamp of .002
295 seconds:
296 touch −d "2007-11-12 10:15:30.002Z" ajosey
298 Create or update a file called cathy; the resulting file has both the
300 last data modification and last data access timestamps set to November
301 12, 2007 at 10:15:00 local time:
302 touch −t 200711121015 cathy
304 Create or update a file called drepper; the resulting file has both the
306 last data modification and last data access timestamps set to November
307 12, 2007 at 10:15:30 local time:
308 touch −t 200711121015.30 drepper
310 Create or update a file called ebb9; the resulting file has both the
312 last data modification and last data access timestamps set to November
313 12, 2007 at 10:15:30 local time:
314 touch −t 0711121015.30 ebb9
316 Create or update a file called eggert; the resulting file has the last
318 data access timestamp set to the corresponding time of the file named
319 mark instead of the current time. If the file exists, the last data
320 modification time is not changed:
321 touch −a −r mark eggert
323
325 The functionality of touch is described almost entirely through refer‐
326 ences to functions in the System Interfaces volume of POSIX.1‐2008. In
327 this way, there is no duplication of effort required for describing
328 such side-effects as the relationship of user IDs to the user database,
329 permissions, and so on.
330 There are some significant differences between the touch utility in
332 this volume of POSIX.1‐2008 and those in System V and BSD systems. They
333 are upwards-compatible for historical applications from both implemen‐
334 tations:
335 1. In System V, an ambiguity exists when a pathname that is a decimal
337 number leads the operands; it is treated as a time value. In BSD,
338 no time value is allowed; files may only be touched to the current
339 time. The −t time construct solves these problems for future con‐
340 forming applications (note that the −t option is not historical
341 practice).
342 2. The inclusion of the century digits, CC, is also new. Note that a
344 ten-digit time value is treated as if YY, and not CC, were speci‐
345 fied. The caveat about the range of dates following the Epoch was
346 included as recognition that some implementations are not able to
347 represent dates beyond 18 January 2038 because they use signed int
348 as a time holder.
349 The −r option was added because several comments requested this capa‐
351 bility. This option was named −f in an early proposal, but was changed
352 because the −f option is used in the BSD version of touch with a dif‐
353 ferent meaning.
354 At least one historical implementation of touch incremented the exit
356 code if −c was specified and the file did not exist. This volume of
357 POSIX.1‐2008 requires exit status zero if no errors occur.
358 In previous version of the standard, if at least two operands are spec‐
360 ified, and the first operand is an eight or ten-digit decimal integer,
361 the first operand was assumed to be a date_time operand. This usage was
362 removed in this version of the standard since it had been marked obso‐
363 lescent previously.
364 The −d date_time format is an ISO 8601:2004 standard complete represen‐
366 tation of date and time extended format with an optional decimal point
367 or <comma> followed by a string of digits following the seconds portion
368 to specify fractions of a second. It is not necessary to recognize
369 "[+/-]hh:mm" and "[+/-]hh" to specify timezones other than local time
370 and UTC. The T time designator in the ISO 8601:2004 standard extended
371 format may be replaced by <space>.
372
374 None.
375
377 date
378 The Base Definitions volume of POSIX.1‐2008, Section 4.15, Seconds
380 Since the Epoch, Chapter 8, Environment Variables, Section 12.2, Util‐
381 ity Syntax Guidelines, <sys_stat.h>
382 The System Interfaces volume of POSIX.1‐2008, creat(), futimens(),
384 time(), utime()
385
387 Portions of this text are reprinted and reproduced in electronic form
388 from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
389 -- Portable Operating System Interface (POSIX), The Open Group Base
390 Specifications Issue 7, Copyright (C) 2013 by the Institute of Electri‐
391 cal and Electronics Engineers, Inc and The Open Group. (This is
392 POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) In the
393 event of any discrepancy between this version and the original IEEE and
394 The Open Group Standard, the original IEEE and The Open Group Standard
395 is the referee document. The original Standard can be obtained online
396 at http://www.unix.org/online.html .
397 Any typographical or formatting errors that appear in this page are
399 most likely to have been introduced during the conversion of the source
400 files to man page format. To report such errors, see https://www.ker‐
401 nel.org/doc/man-pages/reporting_bugs.html .
402IEEE/The Open Group 2013 TOUCH(1P)