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PROLOG | NAME | SYNOPSIS | DESCRIPTION | OPTIONS | OPERANDS | STDIN | INPUT FILES | ENVIRONMENT VARIABLES | ASYNCHRONOUS EVENTS | STDOUT | STDERR | OUTPUT FILES | EXTENDED DESCRIPTION | EXIT STATUS | CONSEQUENCES OF ERRORS | APPLICATION USAGE | EXAMPLES | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT |
TOUCH(1P) POSIX Programmer's Manual TOUCH(1P)
This manual page is part of the POSIX Programmer's Manual. The Linux
implementation of this interface may differ (consult the
corresponding Linux manual page for details of Linux behavior), or
the interface may not be implemented on Linux.
touch — change file access and modification times
touch [−acm] [−r ref_file|−t time|−d date_time] file...
The touch utility shall change the last data modification timestamps,
the last data access timestamps, or both.
The time used can be specified by the −t time option-argument, the
corresponding time fields of the file referenced by the −r ref_file
option-argument, or the −d date_time option-argument, as specified in
the following sections. If none of these are specified, touch shall
use the current time.
For each file operand, touch shall perform actions equivalent to the
following functions defined in the System Interfaces volume of
POSIX.1‐2008:
1. If file does not exist:
a. The creat() function is called with the following arguments:
-- The file operand is used as the path argument.
-- The value of the bitwise-inclusive OR of S_IRUSR,
S_IWUSR, S_IRGRP, S_IWGRP, S_IROTH, and S_IWOTH is used
as the mode argument.
b. The futimens() function is called with the following
arguments:
-- The file descriptor opened in step 1a.
-- The access time and the modification time, set as
described in the OPTIONS section, are used as the first
and second elements of the times array argument,
respectively.
2. If file exists, the utimensat() function is called with the
following arguments:
a. The AT_FDCWD special value is used as the fd argument.
b. The file operand is used as the path argument.
c. The access time and the modification time, set as described
in the OPTIONS section, are used as the first and second
elements of the times array argument, respectively.
d. The flag argument is set to zero.
The touch utility shall conform to the Base Definitions volume of
POSIX.1‐2008, Section 12.2, Utility Syntax Guidelines.
The following options shall be supported:
−a Change the access time of file. Do not change the
modification time unless −m is also specified.
−c Do not create a specified file if it does not exist. Do not
write any diagnostic messages concerning this condition.
−d date_time
Use the specified date_time instead of the current time.
The option-argument shall be a string of the form:
YYYY−MM−DDThh:mm:SS[.frac][tz]
or:
YYYY−MM−DDThh:mm:SS[,frac][tz]
where:
* YYYY are at least four decimal digits giving the year.
* MM, DD, hh, mm, and SS are as with −t time.
* T is the time designator, and can be replaced by a
single <space>.
* [.frac] and [,frac] are either empty, or a <period>
('.') or a <comma> (',') respectively, followed by one
or more decimal digits, specifying a fractional second.
* [tz] is either empty, signifying local time, or the
letter 'Z', signifying UTC. If [tz] is empty, the
resulting time shall be affected by the value of the TZ
environment variable.
If the resulting time precedes the Epoch, the behavior is
implementation-defined. If the time cannot be represented
as the file's timestamp, touch shall exit immediately with
an error status.
−m Change the modification time of file. Do not change the
access time unless −a is also specified.
−r ref_file
Use the corresponding time of the file named by the
pathname ref_file instead of the current time.
−t time Use the specified time instead of the current time. The
option-argument shall be a decimal number of the form:
[[CC]YY]MMDDhhmm[.SS]
where each two digits represents the following:
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].
CC The first two digits of the year (the century).
YY The second two digits of the year.
SS The second of the minute [00,60].
Both CC and YY shall be optional. If neither is given, the
current year shall be assumed. If YY is specified, but CC
is not, CC shall be derived as follows:
┌──────────┬─────────────┐
│If YY is: │ CC becomes: │
├──────────┼─────────────┤
│ [69,99] │ 19 │
│ [00,68] │ 20 │
└──────────┴─────────────┘
Note: It is expected that in a future version of this
standard the default century inferred from a
2-digit year will change. (This would apply to
all commands accepting a 2-digit year as input.)
The resulting time shall be affected by the value of the TZ
environment variable. If the resulting time value precedes
the Epoch, the behavior is implementation-defined. If the
time is out of range for the file's timestamp, touch shall
exit immediately with an error status. The range of valid
times past the Epoch is implementation-defined, but it
shall extend to at least the time 0 hours, 0 minutes, 0
seconds, January 1, 2038, Coordinated Universal Time. Some
implementations may not be able to represent dates beyond
January 18, 2038, because they use signed int as a time
holder.
The range for SS is [00,60] rather than [00,59] because of
leap seconds. If SS is 60, and the resulting time, as
affected by the TZ environment variable, does not refer to
a leap second, the resulting time shall be one second after
a time where SS is 59. If SS is not given a value, it is
assumed to be zero.
If neither the −a nor −m options were specified, touch shall behave
as if both the −a and −m options were specified.
The following operands shall be supported:
file A pathname of a file whose times shall be modified.
Not used.
None.
The following environment variables shall affect the execution of
touch:
LANG Provide a default value for the internationalization
variables that are unset or null. (See the Base Definitions
volume of POSIX.1‐2008, Section 8.2, Internationalization
Variables for the precedence of internationalization
variables used to determine the values of locale
categories.)
LC_ALL If set to a non-empty string value, override the values of
all the other internationalization variables.
LC_CTYPE Determine the locale for the interpretation of sequences of
bytes of text data as characters (for example, single-byte
as opposed to multi-byte characters in arguments).
LC_MESSAGES
Determine the locale that should be used to affect the
format and contents of diagnostic messages written to
standard error.
NLSPATH Determine the location of message catalogs for the
processing of LC_MESSAGES.
TZ Determine the timezone to be used for interpreting the time
option-argument. If TZ is unset or null, an unspecified
default timezone shall be used.
Default.
Not used.
The standard error shall be used only for diagnostic messages.
None.
None.
The following exit values shall be returned:
0 The utility executed successfully and all requested changes
were made.
>0 An error occurred.
Default.
The following sections are informative.
The interpretation of time is taken to be seconds since the Epoch
(see the Base Definitions volume of POSIX.1‐2008, Section 4.15,
Seconds Since the Epoch). It should be noted that implementations
conforming to the System Interfaces volume of POSIX.1‐2008 do not
take leap seconds into account when computing seconds since the
Epoch. When SS=60 is used, the resulting time always refers to 1 plus
seconds since the Epoch for a time when SS=59.
Although the −t time option-argument specifies values in 1969, the
access time and modification time fields are defined in terms of
seconds since the Epoch (00:00:00 on 1 January 1970 UTC). Therefore,
depending on the value of TZ when touch is run, there is never more
than a few valid hours in 1969 and there need not be any valid times
in 1969.
One ambiguous situation occurs if −t time is not specified, −r
ref_file is not specified, and the first operand is an eight or ten-
digit decimal number. A portable script can avoid this problem by
using:
touch −− file
or:
touch ./file
in this case.
If the T time designator is replaced by a <space> for the −d
date_time option-argument, the <space> must be quoted to prevent the
shell from splitting the argument.
Create or update a file called dwc; the resulting file has both the
last data modification and last data access timestamps set to
November 12, 2007 at 10:15:30 local time:
touch −d 2007-11-12T10:15:30 dwc
Create or update a file called nick; the resulting file has both the
last data modification and last data access timestamps set to
November 12, 2007 at 10:15:30 UTC:
touch −d 2007-11-12T10:15:30Z nick
Create or update a file called gwc; the resulting file has both the
last data modification and last data access timestamps set to
November 12, 2007 at 10:15:30 local time with a fractional second
timestamp of .002 seconds:
touch −d 2007-11-12T10:15:30,002 gwc
Create or update a file called ajosey; the resulting file has both
the last data modification and last data access timestamps set to
November 12, 2007 at 10:15:30 UTC with a fractional second timestamp
of .002 seconds:
touch −d "2007-11-12 10:15:30.002Z" ajosey
Create or update a file called cathy; the resulting file has both the
last data modification and last data access timestamps set to
November 12, 2007 at 10:15:00 local time:
touch −t 200711121015 cathy
Create or update a file called drepper; the resulting file has both
the last data modification and last data access timestamps set to
November 12, 2007 at 10:15:30 local time:
touch −t 200711121015.30 drepper
Create or update a file called ebb9; the resulting file has both the
last data modification and last data access timestamps set to
November 12, 2007 at 10:15:30 local time:
touch −t 0711121015.30 ebb9
Create or update a file called eggert; the resulting file has the
last data access timestamp set to the corresponding time of the file
named mark instead of the current time. If the file exists, the last
data modification time is not changed:
touch −a −r mark eggert
The functionality of touch is described almost entirely through
references to functions in the System Interfaces volume of
POSIX.1‐2008. In this way, there is no duplication of effort required
for describing such side-effects as the relationship of user IDs to
the user database, permissions, and so on.
There are some significant differences between the touch utility in
this volume of POSIX.1‐2008 and those in System V and BSD systems.
They are upwards-compatible for historical applications from both
implementations:
1. In System V, an ambiguity exists when a pathname that is a
decimal number leads the operands; it is treated as a time value.
In BSD, no time value is allowed; files may only be touched to
the current time. The −t time construct solves these problems for
future conforming applications (note that the −t option is not
historical practice).
2. The inclusion of the century digits, CC, is also new. Note that a
ten-digit time value is treated as if YY, and not CC, were
specified. The caveat about the range of dates following the
Epoch was included as recognition that some implementations are
not able to represent dates beyond 18 January 2038 because they
use signed int as a time holder.
The −r option was added because several comments requested this
capability. This option was named −f in an early proposal, but was
changed because the −f option is used in the BSD version of touch
with a different meaning.
At least one historical implementation of touch incremented the exit
code if −c was specified and the file did not exist. This volume of
POSIX.1‐2008 requires exit status zero if no errors occur.
In previous version of the standard, if at least two operands are
specified, and the first operand is an eight or ten-digit decimal
integer, the first operand was assumed to be a date_time operand.
This usage was removed in this version of the standard since it had
been marked obsolescent previously.
The −d date_time format is an ISO 8601:2004 standard complete
representation of date and time extended format with an optional
decimal point or <comma> followed by a string of digits following the
seconds portion to specify fractions of a second. It is not necessary
to recognize "[+/-]hh:mm" and "[+/-]hh" to specify timezones other
than local time and UTC. The T time designator in the ISO 8601:2004
standard extended format may be replaced by <space>.
None.
date(1p)
The Base Definitions volume of POSIX.1‐2008, Section 4.15, Seconds
Since the Epoch, Chapter 8, Environment Variables, Section 12.2,
Utility Syntax Guidelines, sys_stat.h(0p)
The System Interfaces volume of POSIX.1‐2008, creat(3p),
futimens(3p), time(3p), utime(3p)
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2013 Edition, Standard for Information
Technology -- Portable Operating System Interface (POSIX), The Open
Group Base Specifications Issue 7, Copyright (C) 2013 by the
Institute of Electrical and Electronics Engineers, Inc and The Open
Group. (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1
applied.) In the event of any discrepancy between this version and
the original IEEE and The Open Group Standard, the original IEEE and
The Open Group Standard is the referee document. The original
Standard can be obtained online at http://www.unix.org/online.html .
Any typographical or formatting errors that appear in this page are
most likely to have been introduced during the conversion of the
source files to man page format. To report such errors, see
https://www.kernel.org/doc/man-pages/reporting_bugs.html .
IEEE/The Open Group 2013 TOUCH(1P)
Pages that refer to this page: qalter(1p), qselect(1p), qsub(1p)