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
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15 touch [-acm][ -r ref_file| -t time] file...
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18 The touch utility shall change the modification times, access times, or
19 both of files. The modification time shall be equivalent to the value
20 of the st_mtime member of the stat structure for a file, as described
21 in the System Interfaces volume of IEEE Std 1003.1-2001; the access
22 time shall be equivalent to the value of st_atime.
23 The time used can be specified by the -t time option-argument, the cor‐
25 responding time fields of the file referenced by the -r ref_file
26 option-argument, or the date_time operand, as specified in the follow‐
27 ing sections. If none of these are specified, touch shall use the cur‐
28 rent time (the value returned by the equivalent of the time() function
29 defined in the System Interfaces volume of IEEE Std 1003.1-2001).
30 For each file operand, touch shall perform actions equivalent to the
32 following functions defined in the System Interfaces volume of
33 IEEE Std 1003.1-2001:
34 1. If file does not exist, a creat() function call is made with the
36 file operand used as the path argument and the value of the bit‐
37 wise-inclusive OR of S_IRUSR, S_IWUSR, S_IRGRP, S_IWGRP, S_IROTH,
38 and S_IWOTH used as the mode argument.
39 2. The utime() function is called with the following arguments:
41 a. The file operand is used as the path argument.
43 b. The utimbuf structure members actime and modtime are determined
45 as described in the OPTIONS section.
46
48 The touch utility shall conform to the Base Definitions volume of
49 IEEE Std 1003.1-2001, Section 12.2, Utility Syntax Guidelines.
50 The following options shall be supported:
52 -a Change the access time of file. Do not change the modification
54 time unless -m is also specified.
55 -c Do not create a specified file if it does not exist. Do not
57 write any diagnostic messages concerning this condition.
58 -m Change the modification time of file. Do not change the access
60 time unless -a is also specified.
61 -r ref_file
63 Use the corresponding time of the file named by the pathname
64 ref_file instead of the current time.
65 -t time
67 Use the specified time instead of the current time. The option-
68 argument shall be a decimal number of the form:
69 [[CC]YY]MMDDhhmm[.SS]
72 where each two digits represents the following:
74 MM
76 The month of the year [01,12].
77 DD
79 The day of the month [01,31].
80 hh
82 The hour of the day [00,23].
83 mm
85 The minute of the hour [00,59].
86 CC
88 The first two digits of the year (the century).
89 YY
91 The second two digits of the year.
92 SS
94 The second of the minute [00,60].
95 Both CC and YY shall be optional. If neither is given, the current year
98 shall be assumed. If YY is specified, but CC is not, CC shall be
99 derived as follows:
100 If YY is: CC becomes:
102 [69,99] 19
103 [00,68] 20
104 Note:
106 It is expected that in a future version of IEEE Std 1003.1-2001
107 the default century inferred from a 2-digit year will change.
108 (This would apply to all commands accepting a 2-digit year as
109 input.)
110 The resulting time shall be affected by the value of the TZ environment
113 variable. If the resulting time value precedes the Epoch, touch shall
114 exit immediately with an error status. The range of valid times past
115 the Epoch is implementation-defined, but it shall extend to at least
116 the time 0 hours, 0 minutes, 0 seconds, January 1, 2038, Coordinated
117 Universal Time. Some implementations may not be able to represent dates
118 beyond January 18, 2038, because they use signed int as a time holder.
119 The range for SS is [00,60] rather than [00,59] because of leap sec‐
121 onds. If SS is 60, and the resulting time, as affected by the TZ envi‐
122 ronment variable, does not refer to a leap second, the resulting time
123 shall be one second after a time where SS is 59. If SS is not given a
124 value, it is assumed to be zero.
125 If neither the -a nor -m options were specified, touch shall behave as
128 if both the -a and -m options were specified.
129
131 The following operands shall be supported:
132 file A pathname of a file whose times shall be modified.
134
137 Not used.
138
140 None.
141
143 The following environment variables shall affect the execution of
144 touch:
145 LANG Provide a default value for the internationalization variables
147 that are unset or null. (See the Base Definitions volume of
148 IEEE Std 1003.1-2001, Section 8.2, Internationalization Vari‐
149 ables for the precedence of internationalization variables used
150 to determine the values of locale categories.)
151 LC_ALL If set to a non-empty string value, override the values of all
153 the other internationalization variables.
154 LC_CTYPE
156 Determine the locale for the interpretation of sequences of
157 bytes of text data as characters (for example, single-byte as
158 opposed to multi-byte characters in arguments).
159 LC_MESSAGES
161 Determine the locale that should be used to affect the format
162 and contents of diagnostic messages written to standard error.
163 NLSPATH
165 Determine the location of message catalogs for the processing of
166 LC_MESSAGES .
167 TZ Determine the timezone to be used for interpreting the time
169 option-argument. If TZ is unset or null, an unspecified default
170 timezone shall be used.
171
174 Default.
175
177 Not used.
178
180 The standard error shall be used only for diagnostic messages.
181
183 None.
184
186 None.
187
189 The following exit values shall be returned:
190 0 The utility executed successfully and all requested changes were
192 made.
193 >0 An error occurred.
195
198 Default.
199 The following sections are informative.
201
203 The interpretation of time is taken to be seconds since the Epoch (see
204 the Base Definitions volume of IEEE Std 1003.1-2001, Section 4.14, Sec‐
205 onds Since the Epoch). It should be noted that implementations conform‐
206 ing to the System Interfaces volume of IEEE Std 1003.1-2001 do not take
207 leap seconds into account when computing seconds since the Epoch. When
208 SS=60 is used, the resulting time always refers to 1 plus seconds since
209 the Epoch for a time when SS=59.
210 Although the -t time option-argument specifies values in 1969, the
212 access time and modification time fields are defined in terms of sec‐
213 onds since the Epoch (00:00:00 on 1 January 1970 UTC). Therefore,
214 depending on the value of TZ when touch is run, there is never more
215 than a few valid hours in 1969 and there need not be any valid times in
216 1969.
217 One ambiguous situation occurs if -t time is not specified, -r ref_file
219 is not specified, and the first operand is an eight or ten-digit deci‐
220 mal number. A portable script can avoid this problem by using:
221 touch -- file
224 or:
226 touch ./file
229 in this case.
231
233 None.
234
236 The functionality of touch is described almost entirely through refer‐
237 ences to functions in the System Interfaces volume of
238 IEEE Std 1003.1-2001. In this way, there is no duplication of effort
239 required for describing such side effects as the relationship of user
240 IDs to the user database, permissions, and so on.
241 There are some significant differences between the touch utility in
243 this volume of IEEE Std 1003.1-2001 and those in System V and BSD sys‐
244 tems. They are upwards-compatible for historical applications from both
245 implementations:
246 1. In System V, an ambiguity exists when a pathname that is a decimal
248 number leads the operands; it is treated as a time value. In BSD,
249 no time value is allowed; files may only be touched to the current
250 time. The -t time construct solves these problems for future con‐
251 forming applications (note that the -t option is not historical
252 practice).
253 2. The inclusion of the century digits, CC, is also new. Note that a
255 ten-digit time value is treated as if YY, and not CC, were speci‐
256 fied. The caveat about the range of dates following the Epoch was
257 included as recognition that some implementations are not able to
258 represent dates beyond 18 January 2038 because they use signed int
259 as a time holder.
260 The -r option was added because several comments requested this capa‐
262 bility. This option was named -f in an early proposal, but was changed
263 because the -f option is used in the BSD version of touch with a dif‐
264 ferent meaning.
265 At least one historical implementation of touch incremented the exit
267 code if -c was specified and the file did not exist. This volume of
268 IEEE Std 1003.1-2001 requires exit status zero if no errors occur.
269
271 Applications should use the -r or -t options.
272
274 date, the System Interfaces volume of IEEE Std 1003.1-2001, creat(),
275 time(), utime(), the Base Definitions volume of IEEE Std 1003.1-2001,
276 <sys/stat.h>
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279 Portions of this text are reprinted and reproduced in electronic form
280 from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
281 -- Portable Operating System Interface (POSIX), The Open Group Base
282 Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
283 Electrical and Electronics Engineers, Inc and The Open Group. In the
284 event of any discrepancy between this version and the original IEEE and
285 The Open Group Standard, the original IEEE and The Open Group Standard
286 is the referee document. The original Standard can be obtained online
287 at http://www.opengroup.org/unix/online.html .
288IEEE/The Open Group 2003 TOUCH(1P)