TOUCH(1)

NAME
touch - change file timestamps

SYNOPSIS
touch [-acm][-r ref_file|-t time] [--] file...

Obsolescent version:
touch [-acm][ugly_time] file...

GNU version:
touch [-acfm] [-r file] [-t decimtime] [-d time] [--time={atime,access,use,mtime,modify}] [--date=time] [--reference=file] [--no-create] [--help] [--version] [--] file...

DESCRIPTION
touch changes the access and/or modification timestamps of each specified file. These timestamps are changed to the current time, unless the -r option is specified, in which case they are changed to the corresponding timestamps of the file ref_file, or the -t option is specified, in which case they are changed to the specified time. Both times are changed when neither or both of the -a and -m options are given. Only the access or only the modification time is changed when one of the options -a and -m is given. If the file did not exist yet, it is created (as an empty file with mode 0666, modified by the umask), unless the -c option is given.

POSIX OPTIONS

-a  Change the access time of file.

-c  Do not create file.

-m  Change the modification time of file.

-r ref_file
    Use the corresponding timestamp of ref_file as the new value for the changed timestamp(s).

-t time
    Use the specified time as the new value for the changed timestamp(s). The argument is a decimal number of the form
        [[CC]YY]MMDDhhmm[.SS]
    with the obvious meaning. If CC is not specified, the year CCYY is taken to be in the range 1969-2068. If SS is not specified, it is taken to be 0. It may be specified in the range 0-61 so that it is possible to refer to leap seconds. The resulting time is taken as a time for the time zone specified by the environment variable TZ. It is an error if the resulting time precedes 1 January 1970.

--  Terminate option list.

POSIX DETAILS
The second form of invocation has the disadvantage that there is some ambiguity as to whether ugly_time is a time or a file argument. It is taken to be a time when no -r or -t option is present, there are at least two arguments, and the first argument is an eight- or ten-digit decimal integer. The format of ugly_time is MMDDhhmm[yy], where an yy in the range 69-99 denotes a year in the range 1969-1999, and an unspecified yy denotes the current year. This form is obsolete.

GNU DETAILS
If the first file would be a valid argument to the -t option and no timestamp is given with any of the -d, -r or -t options and the `--' argument is not given, that argument is interpreted as the time for the other files instead of as a filename.

If changing both the access and modification times to the current time, touch can change the timestamps for files that the user running it does not own but has write permission for. Otherwise, the user must own the files.

GNU OPTIONS

-a, --time=atime, --time=access, --time=use
    Change the access time only.

-c, --no-create
    Do not create files that do not exist.

-d, --date=time
    Use time instead of the current time. It can contain month names, time zones, `am' and `pm', etc.

-f  Ignored; for compatibility with BSD versions of touch(1).

-m, --time=mtime, --time=modify
    Change the modification time only.

-r file, --reference=file
    Use the times of the reference file instead of the current time.

-t decimtime
    Here decimtime has the format MMDDhhmm[[CC]YY][.ss] Use the argument (months, days, hours, minutes, optional century and years, optional seconds) instead of the current time. Note that this format violates the POSIX specification.

GNU STANDARD OPTIONS

--help
    Print a usage message on standard output and exit successfully.

--version
    Print version information on standard output, then exit successfully.

--  Terminate option list.

ENVIRONMENT
The variable TZ is used to interpret explicitly given times. The variables LANG, LC_ALL, LC_CTYPE and LC_MESSAGES have the usual meaning.

CONFORMING TO
POSIX 1003.2 describes a syntax for the argument of the -t option that differs from that used by the GNU implementation.

EXAMPLE OF USE
The command `touch foo' will create the file foo if it didn't exist, and change the time of last modification to now. It is often used to guide the actions of make.

NOTES
This page describes touch as found in the fileutils-4.0 package; other versions may differ slightly.