TOUCH(P) POSIX Programmer's Manual TOUCH(P)
touch - change file access and modification times
touch [-acm][ -r ref_file| -t time] file...
The touch utility shall change the modification times, access times, or both of files. The
modification time shall be equivalent to the value of the st_mtime member of the stat
structure for a file, as described in the System Interfaces volume of
IEEE Std 1003.1-2001; the access time shall be equivalent to the value of st_atime.
The time used can be specified by the -t time option-argument, the corresponding time
fields of the file referenced by the -r ref_file option-argument, or the date_time oper-
and, as specified in the following sections. If none of these are specified, touch shall
use the current time (the value returned by the equivalent of the time() function defined
in the System Interfaces volume of IEEE Std 1003.1-2001).
For each file operand, touch shall perform actions equivalent to the following functions
defined in the System Interfaces volume of IEEE Std 1003.1-2001:
1. If file does not exist, a creat() function call is made with the file operand used as
the path argument and the value of the bitwise-inclusive OR of S_IRUSR, S_IWUSR,
S_IRGRP, S_IWGRP, S_IROTH, and S_IWOTH used as the mode argument.
2. The utime() function is called with the following arguments:
a. The file operand is used as the path argument.
b. The utimbuf structure members actime and modtime are determined as described in
the OPTIONS section.
The touch utility shall conform to the Base Definitions volume of IEEE Std 1003.1-2001,
Section 12.2, Utility Syntax Guidelines.
The following options shall be supported:
-a Change the access time of file. Do not change the modification time unless -m is
-c Do not create a specified file if it does not exist. Do not write any diagnostic
messages concerning this condition.
-m Change the modification time of file. Do not change the access time unless -a is
Use the corresponding time of the file named by the pathname ref_file instead of
the current time.
Use the specified time instead of the current time. The option-argument shall be a
decimal number of the form:
where each two digits represents the following:
The month of the year [01,12].
The day of the month [01,31].
The hour of the day [00,23].
The minute of the hour [00,59].
The first two digits of the year (the century).
The second two digits of the year.
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:
It is expected that in a future version of IEEE Std 1003.1-2001 the default century
inferred from a 2-digit year will change. (This would apply to all commands accept-
ing 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, touch shall exit immediately with an error sta-
tus. 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 implementations 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.
The following operands shall be supported:
file A pathname of a file whose times shall be modified.
The following environment variables shall affect the execution of touch:
LANG Provide a default value for the internationalization variables that are unset or
null. (See the Base Definitions volume of IEEE Std 1003.1-2001, Section 8.2, Inter-
nationalization Variables 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 interna-
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 argu-
Determine the locale that should be used to affect the format and contents of diag-
nostic messages written to standard error.
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.
The standard error shall be used only for diagnostic messages.
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
The following sections are informative.
The interpretation of time is taken to be seconds since the Epoch (see the Base Defini-
tions volume of IEEE Std 1003.1-2001, Section 4.14, Seconds Since the Epoch). It should be
noted that implementations conforming to the System Interfaces volume of
IEEE Std 1003.1-2001 do not take leap seconds 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 modifi-
cation time fields are defined in terms of seconds 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 decimal number. A portable script can avoid
this problem by using:
touch -- file
in this case.
The functionality of touch is described almost entirely through references to functions in
the System Interfaces volume of IEEE Std 1003.1-2001. 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
IEEE Std 1003.1-2001 and those in System V and BSD systems. They are upwards-compatible
for historical applications from both implementations:
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 conforming 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 specified. 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
The -r option was added because several comments requested this capability. 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 different meaning.
At least one historical implementation of touch incremented the exit code if -c was speci-
fied and the file did not exist. This volume of IEEE Std 1003.1-2001 requires exit status
zero if no errors occur.
Applications should use the -r or -t options.
date , the System Interfaces volume of IEEE Std 1003.1-2001, creat(), time(), utime(), the
Base Definitions volume of IEEE Std 1003.1-2001, <sys/stat.h>
Portions of this text are reprinted and reproduced in electronic form from IEEE Std
1003.1, 2003 Edition, Standard for Information Technology -- Portable Operating System
Interface (POSIX), The Open Group Base Specifications Issue 6, Copyright (C) 2001-2003 by
the Institute of Electrical and Electronics Engineers, Inc and The Open Group. 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 orig-
inal Standard can be obtained online at http://www.opengroup.org/unix/online.html .
IEEE/The Open Group 2003 TOUCH(P)