touch - change file access, modification and status change times

touch changes the modification time, access time or both of each file. The modification time is the st_mtime member of the stat(2) information and the access time is the st_atime member. On most systems the file status change time is always set to the current time when either the access or modification times are changed.

If neither the --reference nor the --time options are specified then the time used will be the date operand or the current time if date is omitted.

If the date operand consists of 4, 6, 8, 10 or 12 digits followed by an optional . and two digits then it is interpreted as: HHMM.SS, ddHHMM.SS, mmddHHMM.SS, mmddHHMMyy.SS or yymmddHHMM.SS, or mmddHHMMccyy.SS or ccyymmddHHMM.SS. Conflicting standards and practice allow a leading or trailing 2 or 4 digit year for the 10 and 12 digit forms; the X/Open leading form is used to disambiguate (date(1) uses the trailing form.) Avoid the 10 digit form to avoid confusion. The digit fields are:

cc

Century - 1, 19-20.

yy

Year in century, 00-99.

mm

Month, 01-12.

dd

Day of month, 01-31.

HH

Hour, 00-23.

MM

Minute, 00-59.

SS

Seconds, 00-60.

-a, --access|atime|use

Change the access time. Do not change the modification time unless --modify is also specified.

-c, --create

Create the file if it does not exist, but write no diagnostic. On by default; -c means --nocreate.

-f, --force

Ignored by this implementation.

-m, --modify|mtime|modification

Change the modify time. Do not change the access time unless --access is also specified.

-r, --reference=file

Use the corresponding time of file instead of the current time.

-s|n, --change|ctime|neither

Change only the file status change time st_ctime. Most systems summarily set st_ctime to the current time.

-t|d, --time|date=date-time

Use the specified date-time instead of the current date-time. Most common formats are accepted. See tmdate(3) for details. If date-time consists of 4, 6, 8, 10 or 12 digits followed by an optional . and 2 digits and another optional . and 1 or more digits then it is interpreted as the date operand above, except that the leading 2 or 4 digit year form is used to disambiguate. Avoid the 10 digit form to avoid confusion. If --reference is specified or if file already exists then time may also be one of:

access|atime|use

The access time of the reference file.

change|ctime

The change time of the reference file.

modify|mtime|modification

The modify time of the reference file.

-v, --verbose

Write a diagnostic for each nonexistent file.

Some systems or file system types may limit the range of times that can be set. These limitations may not show up until a subsequent stat(2) call (yes, the time can be set but not checked!) Upper limits of <0xffffffff and <0x7fffffff have been observed.

date(1), nmake(1), utime(2), tm(3)

version

touch (AT&T Research) 2004-12-12

author

Glenn Fowler <gsf@research.att.com>

copyright

Copyright © 1989-2012 AT&T Intellectual Property

license

http://www.eclipse.org/org/documents/epl-v10.html