touch(1)touch(1)NAMEtouch - update access, modification, and/or change times of file
SYNOPSIS
ref_file time] file_name...
Obsolescent
time_str file_name...
DESCRIPTION
updates the access, modification, and last-change times of each argu‐
ment. The file name is created if it does not exist. If no time is
specified (see date(1)) the current time is used.
The and options are mutually exclusive.
Options
The following options are available:
Change the access time of
file_name to time, or to the current time if time
is not specified. Do not change the modification
time unless is also specified.
Change the modification time of
file_name to time, or to the current time if time
is not specified. Do not change the access time
unless is also specified.
Silently prevent
from creating the file if it did not previously
exist. Do not write any diagnostic messages con‐
cerning this condition.
Use the corresponding time of
ref_file instead of the current time.
Use the specified
time instead of the current time. The option
argument is a decimal number of the form:
[[CC]YY]MMDDhhmm[.SS]
where each two digits represents the following:
CC The first two digits of the year.
YY The second two digits of the year.
MM The month of the year (01-12).
DD The day of the month (01-31).
hh The hour of the day (00-23).
mm The minute of the hour (00-59).
SS The second of the minute (00-61).
If neither CC nor YY is given, the current year
is assumed. If YY is specified, but CC is not,
CC is derived as follows: (taken into account the
local time factor)
If YY is: CC becomes:
────────────────────────
69-99 19
00-68 20
If the resulting time value precedes the Epoch
(00:00:00 January 1, 1970 Greenwich Mean Time),
exits immediately with an error status.
The range for SS is 00 through 61 rather than 00
through 59 to accommodate leap seconds. If SS is
60 or 61, and the resulting time, as affected by
the environment variable, does not refer to a
leap second, the resulting time is one second
after a time where SS is 59. If SS is not given
a value, it is assumed to be 0.
The syntax shown by the second line is recognized when neither the
option, the option, nor the option delimiter is specified, and the
first operand consists of all decimal digits. This operand is inter‐
preted as the time argument instead of as a file name. However, in
this case, time_str is assumed to be of the form:
MMDDhhmm[YY]
This is for backward compatibility. The form given above is recom‐
mended for future portability. The option delimiter can be used before
the first file_name if there is a possibility that file_name consists
of all digits, in order to ensure that the first syntax is used.
succeeds when invoked by the of the file if any of the following are
true:
· A time is specified.
· Only the access time of the file is being updated.
· Only the modification time of the file is being updated.
In addition, succeeds when invoked by a user with write permission on
the file if of the following are true:
· No time is specified.
· the access time and modification time of the file are being
updated.
EXTERNAL INFLUENCES
Environment Variables
If the time is specified via the
option, is used to interpret the time for the specified time
zone.
determines the language in which messages are displayed.
If is not specified in the environment or is set to the empty string,
the value of is used as a default for each unspecified or empty vari‐
able. If is not specified or is set to the empty string, a default of
"C" (see lang(5)) is used instead of
If any internationalization variable contains an invalid setting,
behaves as if all internationalization variables are set to "C". See
environ(5).
International Code Set Support
Single- and multibyte character code sets are supported.
RETURN VALUE
returns the following values:
All file_name arguments were successfully changed.
Prints out a diagnostic message
if an invalid time or a time earlier than the Epoch was
specified with the option, or if the and options were
both specified, or if one or more of the file_name argu‐
ments could not be accessed.
EXAMPLES
The following command sets the modification and access times of the
file named "bastille" to midnight, July 14, 1989, creating the file if
it does not already exist.
The following command does the same thing using the backward-compatible
syntax:
The following command sets the time of the two files named "0714000089"
and "bastille" to the current time, creating them if they do not exist:
To create a zero-length file, use any of the following:
DEPENDENCIES
NFS
An attempt to touch a file owned by the superuser on a remote server
can fail, even if the invoking user has write permission on the file.
SEE ALSOdate(1), utime(2).
STANDARDS CONFORMANCEtouch(1)
