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
12 touch — change file access and modification times
13
15 touch [-acm] [-r ref_file|-t time|-d date_time] file...
16
18 The touch utility shall change the last data modification timestamps,
19 the last data access timestamps, or both.
20 The time used can be specified by the -t time option-argument, the cor‐
22 responding time fields of the file referenced by the -r ref_file
23 option-argument, or the -d date_time option-argument, as specified in
24 the following sections. If none of these are specified, touch shall use
25 the current time.
26 For each file operand, touch shall perform actions equivalent to the
28 following functions defined in the System Interfaces volume of
29 POSIX.1‐2017:
30 1. If file does not exist:
32 a. The creat() function is called with the following arguments:
34 -- The file operand is used as the path argument.
36 -- The value of the bitwise-inclusive OR of S_IRUSR, S_IWUSR,
38 S_IRGRP, S_IWGRP, S_IROTH, and S_IWOTH is used as the mode
39 argument.
40 b. The futimens() function is called with the following arguments:
42 -- The file descriptor opened in step 1a.
44 -- The access time and the modification time, set as described
46 in the OPTIONS section, are used as the first and second
47 elements of the times array argument, respectively.
48 2. If file exists, the utimensat() function is called with the follow‐
50 ing arguments:
51 a. The AT_FDCWD special value is used as the fd argument.
53 b. The file operand is used as the path argument.
55 c. The access time and the modification time, set as described in
57 the OPTIONS section, are used as the first and second elements
58 of the times array argument, respectively.
59 d. The flag argument is set to zero.
61
63 The touch utility shall conform to the Base Definitions volume of
64 POSIX.1‐2017, Section 12.2, Utility Syntax Guidelines.
65 The following options shall be supported:
67 -a Change the access time of file. Do not change the modifica‐
69 tion time unless -m is also specified.
70 -c Do not create a specified file if it does not exist. Do not
72 write any diagnostic messages concerning this condition.
73 -d date_time
75 Use the specified date_time instead of the current time. The
76 option-argument shall be a string of the form:
77 YYYY-MM-DDThh:mm:SS[.frac][tz]
80 or:
82 YYYY-MM-DDThh:mm:SS[,frac][tz]
85 where:
87 * YYYY are at least four decimal digits giving the year.
89 * MM, DD, hh, mm, and SS are as with -t time.
91 * T is the time designator, and can be replaced by a single
93 <space>.
94 * [.frac] and [,frac] are either empty, or a <period> ('.')
96 or a <comma> (',') respectively, followed by one or more
97 decimal digits, specifying a fractional second.
98 * [tz] is either empty, signifying local time, or the let‐
100 ter 'Z', signifying UTC. If [tz] is empty, the resulting
101 time shall be affected by the value of the TZ environment
102 variable.
103 If the resulting time precedes the Epoch, the behavior is
105 implementation-defined. If the time cannot be represented as
106 the file's timestamp, touch shall exit immediately with an
107 error status.
108 -m Change the modification time of file. Do not change the
110 access time unless -a is also specified.
111 -r ref_file
113 Use the corresponding time of the file named by the pathname
114 ref_file instead of the current time.
115 -t time Use the specified time instead of the current time. The
117 option-argument shall be a decimal number of the form:
118 [[CC]YY]MMDDhhmm[.SS]
121 where each two digits represents the following:
123 MM The month of the year [01,12].
125 DD The day of the month [01,31].
127 hh The hour of the day [00,23].
129 mm The minute of the hour [00,59].
131 CC The first two digits of the year (the century).
133 YY The second two digits of the year.
135 SS The second of the minute [00,60].
137 Both CC and YY shall be optional. If neither is given, the
139 current year shall be assumed. If YY is specified, but CC is
140 not, CC shall be derived as follows:
141 ┌──────────┬─────────────┐
143 │If YY is: │ CC becomes: │
144 ├──────────┼─────────────┤
145 │ [69,99] │ 19 │
146 │ [00,68] │ 20 │
147 └──────────┴─────────────┘
148 Note: It is expected that in a future version of this
149 standard the default century inferred from a
150 2-digit year will change. (This would apply to all
151 commands accepting a 2-digit year as input.)
152 The resulting time shall be affected by the value of the TZ
154 environment variable. If the resulting time value precedes
155 the Epoch, the behavior is implementation-defined. If the
156 time is out of range for the file's timestamp, touch shall
157 exit immediately with an error status. The range of valid
158 times past the Epoch is implementation-defined, but it shall
159 extend to at least the time 0 hours, 0 minutes, 0 seconds,
160 January 1, 2038, Coordinated Universal Time. Some implementa‐
161 tions may not be able to represent dates beyond January 18,
162 2038, because they use signed int as a time holder.
163 The range for SS is [00,60] rather than [00,59] because of
165 leap seconds. If SS is 60, and the resulting time, as
166 affected by the TZ environment variable, does not refer to a
167 leap second, the resulting time shall be one second after a
168 time where SS is 59. If SS is not given a value, it is
169 assumed to be zero.
170 If neither the -a nor -m options were specified, touch shall behave as
172 if both the -a and -m options were specified.
173
175 The following operands shall be supported:
176 file A pathname of a file whose times shall be modified.
178
180 Not used.
181
183 None.
184
186 The following environment variables shall affect the execution of
187 touch:
188 LANG Provide a default value for the internationalization vari‐
190 ables that are unset or null. (See the Base Definitions vol‐
191 ume of POSIX.1‐2017, Section 8.2, Internationalization Vari‐
192 ables for the precedence of internationalization variables
193 used to determine the values of locale categories.)
194 LC_ALL If set to a non-empty string value, override the values of
196 all the other internationalization variables.
197 LC_CTYPE Determine the locale for the interpretation of sequences of
199 bytes of text data as characters (for example, single-byte as
200 opposed to multi-byte characters in arguments).
201 LC_MESSAGES
203 Determine the locale that should be used to affect the format
204 and contents of diagnostic messages written to standard
205 error.
206 NLSPATH Determine the location of message catalogs for the processing
208 of LC_MESSAGES.
209 TZ Determine the timezone to be used for interpreting the time
211 option-argument. If TZ is unset or null, an unspecified
212 default timezone shall be used.
213
215 Default.
216
218 Not used.
219
221 The standard error shall be used only for diagnostic messages.
222
224 None.
225
227 None.
228
230 The following exit values shall be returned:
231 0 The utility executed successfully and all requested changes were
233 made.
234 >0 An error occurred.
236
238 Default.
239 The following sections are informative.
241
243 The interpretation of time is taken to be seconds since the Epoch (see
244 the Base Definitions volume of POSIX.1‐2017, Section 4.16, Seconds
245 Since the Epoch). It should be noted that implementations conforming
246 to the System Interfaces volume of POSIX.1‐2017 do not take leap sec‐
247 onds into account when computing seconds since the Epoch. When SS=60 is
248 used, the resulting time always refers to 1 plus seconds since the
249 Epoch for a time when SS=59.
250 Although the -t time option-argument specifies values in 1969, the
252 access time and modification time fields are defined in terms of sec‐
253 onds since the Epoch (00:00:00 on 1 January 1970 UTC). Therefore,
254 depending on the value of TZ when touch is run, there is never more
255 than a few valid hours in 1969 and there need not be any valid times in
256 1969.
257 If the T time designator is replaced by a <space> for the -d date_time
259 option-argument, the <space> must be quoted to prevent the shell from
260 splitting the argument.
261
263 Create or update a file called dwc; the resulting file has both the
264 last data modification and last data access timestamps set to November
265 12, 2007 at 10:15:30 local time:
266 touch -d 2007-11-12T10:15:30 dwc
269 Create or update a file called nick; the resulting file has both the
271 last data modification and last data access timestamps set to November
272 12, 2007 at 10:15:30 UTC:
273 touch -d 2007-11-12T10:15:30Z nick
276 Create or update a file called gwc; the resulting file has both the
278 last data modification and last data access timestamps set to November
279 12, 2007 at 10:15:30 local time with a fractional second timestamp of
280 .002 seconds:
281 touch -d 2007-11-12T10:15:30,002 gwc
284 Create or update a file called ajosey; 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 UTC with a fractional second timestamp of .002
288 seconds:
289 touch -d "2007-11-12 10:15:30.002Z" ajosey
292 Create or update a file called cathy; the resulting file has both the
294 last data modification and last data access timestamps set to November
295 12, 2007 at 10:15:00 local time:
296 touch -t 200711121015 cathy
299 Create or update a file called drepper; the resulting file has both the
301 last data modification and last data access timestamps set to November
302 12, 2007 at 10:15:30 local time:
303 touch -t 200711121015.30 drepper
306 Create or update a file called ebb9; the resulting file has both the
308 last data modification and last data access timestamps set to November
309 12, 2007 at 10:15:30 local time:
310 touch -t 0711121015.30 ebb9
313 Create or update a file called eggert; the resulting file has the last
315 data access timestamp set to the corresponding time of the file named
316 mark instead of the current time. If the file exists, the last data
317 modification time is not changed:
318 touch -a -r mark eggert
321
323 The functionality of touch is described almost entirely through refer‐
324 ences to functions in the System Interfaces volume of POSIX.1‐2017. In
325 this way, there is no duplication of effort required for describing
326 such side-effects as the relationship of user IDs to the user database,
327 permissions, and so on.
328 There are some significant differences between the touch utility in
330 this volume of POSIX.1‐2017 and those in System V and BSD systems. They
331 are upwards-compatible for historical applications from both implemen‐
332 tations:
333 1. In System V, an ambiguity exists when a pathname that is a decimal
335 number leads the operands; it is treated as a time value. In BSD,
336 no time value is allowed; files may only be touched to the current
337 time. The -t time construct solves these problems for future con‐
338 forming applications (note that the -t option is not historical
339 practice).
340 2. The inclusion of the century digits, CC, is also new. Note that a
342 ten-digit time value is treated as if YY, and not CC, were speci‐
343 fied. The caveat about the range of dates following the Epoch was
344 included as recognition that some implementations are not able to
345 represent dates beyond 18 January 2038 because they use signed int
346 as a time holder.
347 The -r option was added because several comments requested this capa‐
349 bility. This option was named -f in an early proposal, but was changed
350 because the -f option is used in the BSD version of touch with a dif‐
351 ferent meaning.
352 At least one historical implementation of touch incremented the exit
354 code if -c was specified and the file did not exist. This volume of
355 POSIX.1‐2017 requires exit status zero if no errors occur.
356 In previous version of the standard, if at least two operands are spec‐
358 ified, and the first operand is an eight or ten-digit decimal integer,
359 the first operand was assumed to be a date_time operand. This usage was
360 removed in this version of the standard since it had been marked obso‐
361 lescent previously.
362 The -d date_time format is an ISO 8601:2004 standard complete represen‐
364 tation of date and time extended format with an optional decimal point
365 or <comma> followed by a string of digits following the seconds portion
366 to specify fractions of a second. It is not necessary to recognize
367 "[+/-]hh:mm" and "[+/-]hh" to specify timezones other than local time
368 and UTC. The T time designator in the ISO 8601:2004 standard extended
369 format may be replaced by <space>.
370
372 None.
373
375 date
376 The Base Definitions volume of POSIX.1‐2017, Section 4.16, Seconds
378 Since the Epoch, Chapter 8, Environment Variables, Section 12.2, Util‐
379 ity Syntax Guidelines, <sys_stat.h>
380 The System Interfaces volume of POSIX.1‐2017, creat(), futimens(),
382 time(), utime()
383
385 Portions of this text are reprinted and reproduced in electronic form
386 from IEEE Std 1003.1-2017, Standard for Information Technology -- Por‐
387 table Operating System Interface (POSIX), The Open Group Base Specifi‐
388 cations Issue 7, 2018 Edition, Copyright (C) 2018 by the Institute of
389 Electrical and Electronics Engineers, Inc and The Open Group. In the
390 event of any discrepancy between this version and the original IEEE and
391 The Open Group Standard, the original IEEE and The Open Group Standard
392 is the referee document. The original Standard can be obtained online
393 at http://www.opengroup.org/unix/online.html .
394 Any typographical or formatting errors that appear in this page are
396 most likely to have been introduced during the conversion of the source
397 files to man page format. To report such errors, see https://www.ker‐
398 nel.org/doc/man-pages/reporting_bugs.html .
399IEEE/The Open Group 2017 TOUCH(1P)