touch -- change file modification date

touch change file modification date	Command

SYNOPSIS

touch [-acm] [-f agefile] [-r agefile] [[-t] time] file ...

touch [-acm] time file ...

The touch command changes certain dates for each file argument. By default, touch sets both the date of last file modification and the date of last file access to the current time. This is useful for maintaining correct release times for software and is particularly useful in conjunction with the MKS Make software development facility.

Options

-a: sets only the access time.
-c: does not create any files that do not already exist. Normally, touch creates such files.
-m: sets only the modification time.

If you do not specify -a or -m, touch behaves as though you specified both.

To tell touch to use a time other than the current, use one of the following options:

-f agefile

is an obsolete version of the POSIX-compliant -r option.

-r agefile

sets the access and modification times (as indicated by the other options) to those kept for agefile.

-t time

specifies a particular time using this format:

[[[[cc]yy]MM]dd]hhmm[.ss]

where cc is the optional first 2 digits of the year, yy is the optional last 2 digits of the year, MM is the optional number of the month (01-12), dd is the optional day of the month, hh is the hour in 24 hour format (required), mm is the minutes (required), ss is the optional seconds.

An obsolete (but still supported) version of this command lets you omit the -t, but the format is:

MMddhhmmyy[yy]

EXAMPLES

touch newfile

sets the modification time of newfile to the present.

touch -t 8001031305 oldfile

sets the modification time of oldfile to 13:05 on January 3, 1980.

touch -r oldfile newfile

sets the modification time of newfile to that of oldfile.

ENVIRONMENT VARIABLES

TZ: contains the time zone that touch is to use when interpreting times.

DIAGNOSTICS

Possible exit status values are:

0

Successful completion.

1

Failure due to any of the following:

— inability to access the desired file

— system cannot support such an early date

— inability to create a file

— inability to change a file's times

2

Failure that resulted in a usage message, including:

— unknown command line option

— only one of -t, -f, or -r is allowed

— -r was missing the agefile

— -t was missing its argument

— invalid date string (bad date conversion)

Messages

Age file inaccessible: indicates that time could not be found for the file given with the -f or -r option either because that file does not exist or because the requesting user is not granted the appropriate permission for the file.
Missing age file argument: You specified -f or -r, but did not give a file name after it.
Years earlier than year invalid: Your system only recognizes dates back to the given year. touch does not accept dates before that time.
Bad date conversion
Only one -r(-f) or -t flag allowed
Missing date/time argument: Self-explanatory.

PORTABILITY

POSIX.2. x/OPEN Portability Guide 4.0.

touch

Command