TOUCH(1P) POSIX Programmer's Manual TOUCH(1P)
PROLOG
This manual page is part of the POSIX Programmer's Manual. The Linux
implementation of this interface may differ (consult the corresponding
Linux manual page for details of Linux behavior), or the interface may
not be implemented on Linux.
NAME
touch -- change file access and modification times
SYNOPSIS
touch [-acm] [-r ref_file|-t time|-d date_time] file...
DESCRIPTION
The touch utility shall change the last data modification timestamps,
the last data access timestamps, or both.
The time used can be specified by the -t time option-argument, the cor-
responding time fields of the file referenced by the -r ref_file
option-argument, or the -d date_time option-argument, as specified in
the following sections. If none of these are specified, touch shall use
the current time.
For each file operand, touch shall perform actions equivalent to the
following functions defined in the System Interfaces volume of
POSIX.1-2008:
1. If file does not exist:
a. The creat() function is called with the following arguments:
-- The file operand is used as the path argument.
-- The value of the bitwise-inclusive OR of S_IRUSR, S_IWUSR,
S_IRGRP, S_IWGRP, S_IROTH, and S_IWOTH is used as the mode
argument.
b. The futimens() function is called with the following arguments:
-- The file descriptor opened in step 1a.
-- The access time and the modification time, set as described
in the OPTIONS section, are used as the first and second
elements of the times array argument, respectively.
2. If file exists, the utimensat() function is called with the follow-
ing arguments:
a. The AT_FDCWD special value is used as the fd argument.
b. The file operand is used as the path argument.
c. The access time and the modification time, set as described in
the OPTIONS section, are used as the first and second elements
of the times array argument, respectively.
d. The flag argument is set to zero.
OPTIONS
The touch utility shall conform to the Base Definitions volume of
POSIX.1-2008, Section 12.2, Utility Syntax Guidelines.
The following options shall be supported:
-a Change the access time of file. Do not change the modifica-
tion time unless -m is also specified.
-c Do not create a specified file if it does not exist. Do not
write any diagnostic messages concerning this condition.
-d date_time
Use the specified date_time instead of the current time. The
option-argument shall be a string of the form:
YYYY-MM-DDThh:mm:SS[.frac][tz]
or:
YYYY-MM-DDThh:mm:SS[,frac][tz]
where:
* YYYY are at least four decimal digits giving the year.
* MM, DD, hh, mm, and SS are as with -t time.
* T is the time designator, and can be replaced by a single
<space>.
* [.frac] and [,frac] are either empty, or a <period> ('.')
or a <comma> (',') respectively, followed by one or more
decimal digits, specifying a fractional second.
* [tz] is either empty, signifying local time, or the let-
ter 'Z', signifying UTC. If [tz] is empty, the resulting
time shall be affected by the value of the TZ environment
variable.
If the resulting time precedes the Epoch, the behavior is
implementation-defined. If the time cannot be represented as
the file's timestamp, touch shall exit immediately with an
error status.
-m Change the modification time of file. Do not change the
access time unless -a is also specified.
-r ref_file
Use the corresponding time of the file named by the pathname
ref_file instead of the current time.
-t time Use the specified time instead of the current time. The
option-argument shall be a decimal number of the form:
[[CC]YY]MMDDhhmm[.SS]
where each two digits represents the following:
MM The month of the year [01,12].
DD The day of the month [01,31].
hh The hour of the day [00,23].
mm The minute of the hour [00,59].
CC The first two digits of the year (the century).
YY The second two digits of the year.
SS The second of the minute [00,60].
Both CC and YY shall be optional. If neither is given, the
current year shall be assumed. If YY is specified, but CC is
not, CC shall be derived as follows:
+----------+-------------+
|If YY is: | CC becomes: |
+----------+-------------+
| [69,99] | 19 |
| [00,68] | 20 |
+----------+-------------+
Note: It is expected that in a future version of this
standard the default century inferred from a
2-digit year will change. (This would apply to all
commands accepting a 2-digit year as input.)
The resulting time shall be affected by the value of the TZ
environment variable. If the resulting time value precedes
the Epoch, the behavior is implementation-defined. If the
time is out of range for the file's timestamp, touch shall
exit immediately with an error status. The range of valid
times past the Epoch is implementation-defined, but it shall
extend to at least the time 0 hours, 0 minutes, 0 seconds,
January 1, 2038, Coordinated Universal Time. Some implementa-
tions may not be able to represent dates beyond January 18,
2038, because they use signed int as a time holder.
The range for SS is [00,60] rather than [00,59] because of
leap seconds. If SS is 60, and the resulting time, as
affected by the TZ environment variable, does not refer to a
leap second, the resulting time shall be one second after a
time where SS is 59. If SS is not given a value, it is
assumed to be zero.
If neither the -a nor -m options were specified, touch shall behave as
if both the -a and -m options were specified.
OPERANDS
The following operands shall be supported:
file A pathname of a file whose times shall be modified.
STDIN
Not used.
INPUT FILES
None.
ENVIRONMENT VARIABLES
The following environment variables shall affect the execution of
touch:
LANG Provide a default value for the internationalization vari-
ables that are unset or null. (See the Base Definitions vol-
ume of POSIX.1-2008, Section 8.2, Internationalization Vari-
ables for the precedence of internationalization variables
used to determine the values of locale categories.)
LC_ALL If set to a non-empty string value, override the values of
all the other internationalization variables.
LC_CTYPE Determine the locale for the interpretation of sequences of
bytes of text data as characters (for example, single-byte as
opposed to multi-byte characters in arguments).
LC_MESSAGES
Determine the locale that should be used to affect the format
and contents of diagnostic messages written to standard
error.
NLSPATH Determine the location of message catalogs for the processing
of LC_MESSAGES.
TZ Determine the timezone to be used for interpreting the time
option-argument. If TZ is unset or null, an unspecified
default timezone shall be used.
ASYNCHRONOUS EVENTS
Default.
STDOUT
Not used.
STDERR
The standard error shall be used only for diagnostic messages.
OUTPUT FILES
None.
EXTENDED DESCRIPTION
None.
EXIT STATUS
The following exit values shall be returned:
0 The utility executed successfully and all requested changes were
made.
>0 An error occurred.
CONSEQUENCES OF ERRORS
Default.
The following sections are informative.
APPLICATION USAGE
The interpretation of time is taken to be seconds since the Epoch (see
the Base Definitions volume of POSIX.1-2008, Section 4.15, Seconds
Since the Epoch). It should be noted that implementations conforming
to the System Interfaces volume of POSIX.1-2008 do not take leap sec-
onds into account when computing seconds since the Epoch. When SS=60 is
used, the resulting time always refers to 1 plus seconds since the
Epoch for a time when SS=59.
Although the -t time option-argument specifies values in 1969, the
access time and modification time fields are defined in terms of sec-
onds since the Epoch (00:00:00 on 1 January 1970 UTC). Therefore,
depending on the value of TZ when touch is run, there is never more
than a few valid hours in 1969 and there need not be any valid times in
1969.
One ambiguous situation occurs if -t time is not specified, -r ref_file
is not specified, and the first operand is an eight or ten-digit deci-
mal number. A portable script can avoid this problem by using:
touch -- file
or:
touch ./file
in this case.
If the T time designator is replaced by a <space> for the -d date_time
option-argument, the <space> must be quoted to prevent the shell from
splitting the argument.
EXAMPLES
Create or update a file called dwc; the resulting file has both the
last data modification and last data access timestamps set to November
12, 2007 at 10:15:30 local time:
touch -d 2007-11-12T10:15:30 dwc
Create or update a file called nick; the resulting file has both the
last data modification and last data access timestamps set to November
12, 2007 at 10:15:30 UTC:
touch -d 2007-11-12T10:15:30Z nick
Create or update a file called gwc; the resulting file has both the
last data modification and last data access timestamps set to November
12, 2007 at 10:15:30 local time with a fractional second timestamp of
.002 seconds:
touch -d 2007-11-12T10:15:30,002 gwc
Create or update a file called ajosey; the resulting file has both the
last data modification and last data access timestamps set to November
12, 2007 at 10:15:30 UTC with a fractional second timestamp of .002
seconds:
touch -d "2007-11-12 10:15:30.002Z" ajosey
Create or update a file called cathy; the resulting file has both the
last data modification and last data access timestamps set to November
12, 2007 at 10:15:00 local time:
touch -t 200711121015 cathy
Create or update a file called drepper; the resulting file has both the
last data modification and last data access timestamps set to November
12, 2007 at 10:15:30 local time:
touch -t 200711121015.30 drepper
Create or update a file called ebb9; the resulting file has both the
last data modification and last data access timestamps set to November
12, 2007 at 10:15:30 local time:
touch -t 0711121015.30 ebb9
Create or update a file called eggert; the resulting file has the last
data access timestamp set to the corresponding time of the file named
mark instead of the current time. If the file exists, the last data
modification time is not changed:
touch -a -r mark eggert
RATIONALE
The functionality of touch is described almost entirely through refer-
ences to functions in the System Interfaces volume of POSIX.1-2008. In
this way, there is no duplication of effort required for describing
such side-effects as the relationship of user IDs to the user database,
permissions, and so on.
There are some significant differences between the touch utility in
this volume of POSIX.1-2008 and those in System V and BSD systems. They
are upwards-compatible for historical applications from both implemen-
tations:
1. In System V, an ambiguity exists when a pathname that is a decimal
number leads the operands; it is treated as a time value. In BSD,
no time value is allowed; files may only be touched to the current
time. The -t time construct solves these problems for future con-
forming applications (note that the -t option is not historical
practice).
2. The inclusion of the century digits, CC, is also new. Note that a
ten-digit time value is treated as if YY, and not CC, were speci-
fied. The caveat about the range of dates following the Epoch was
included as recognition that some implementations are not able to
represent dates beyond 18 January 2038 because they use signed int
as a time holder.
The -r option was added because several comments requested this capa-
bility. This option was named -f in an early proposal, but was changed
because the -f option is used in the BSD version of touch with a dif-
ferent meaning.
At least one historical implementation of touch incremented the exit
code if -c was specified and the file did not exist. This volume of
POSIX.1-2008 requires exit status zero if no errors occur.
In previous version of the standard, if at least two operands are spec-
ified, and the first operand is an eight or ten-digit decimal integer,
the first operand was assumed to be a date_time operand. This usage was
removed in this version of the standard since it had been marked obso-
lescent previously.
The -d date_time format is an ISO 8601:2004 standard complete represen-
tation of date and time extended format with an optional decimal point
or <comma> followed by a string of digits following the seconds portion
to specify fractions of a second. It is not necessary to recognize
"[+/-]hh:mm" and "[+/-]hh" to specify timezones other than local time
and UTC. The T time designator in the ISO 8601:2004 standard extended
format may be replaced by <space>.
FUTURE DIRECTIONS
None.
SEE ALSO
date
The Base Definitions volume of POSIX.1-2008, Section 4.15, Seconds
Since the Epoch, Chapter 8, Environment Variables, Section 12.2, Util-
ity Syntax Guidelines, <sys_stat.h>
The System Interfaces volume of POSIX.1-2008, creat(), futimens(),
time(), utime()
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 7, Copyright (C) 2013 by the Institute of Electri-
cal and Electronics Engineers, Inc and The Open Group. (This is
POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) In the
event of any discrepancy between this version and the original IEEE and
The Open Group Standard, the original IEEE and The Open Group Standard
is the referee document. The original Standard can be obtained online
at http://www.unix.org/online.html .
Any typographical or formatting errors that appear in this page are
most likely to have been introduced during the conversion of the source
files to man page format. To report such errors, see https://www.ker-
nel.org/doc/man-pages/reporting_bugs.html .
IEEE/The Open Group 2013 TOUCH(1P)
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