touch — Change the file access and modification times

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

Purpose

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 make command.

Options

–a
Sets only the access time.
–c
Does not create any file that does 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 –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 first two digits of the year (optional)
  • yy is the last two digits of the year (optional)
  • mm is the number of the month (01—12) (optional)
  • dd is the day of the month (optional)
  • hh is the hour in 24-hour format (required)
  • mm is the minutes (required)
  • ss is the seconds (optional)
An obsolete (but still supported) version of this command lets you omit the –t, but the format is: 
[[mm]dd]hhmm[.ss]
or: 
mmddhhmmyy[.ss]

Examples

  1. To set the modification time of newfile to the present, enter: 
    touch newfile
  2. To set the modification time of oldfile to 13:05 on July 3, 1994, enter: 
    touch -t 9407031305 oldfile
  3. To set the modification time of newfile to that of oldfile, enter: 
    touch -r oldfile newfile

Environment Variables

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

Localization

touch uses the following localization environment variables:
  • LANG
  • LC_ALL
  • LC_CTYPE
  • LC_MESSAGES
See Localization for more information.

Exit Values

Possible exit status values are:
0
Successful completion
1
Failure due to any of the following:
  • Inability to access the desired file
  • Too early a date was specified
  • 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
  • Incorrect date string

Messages and Return Codes

Possible error messages include:
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 incorrect
Your system recognizes dates only 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 the date or time argument
 

Portability

POSIX.2, X/Open Portability Guide, UNIX systems.

Related Commands

cp, date