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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 |
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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.1‐2017:
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.1‐2017, 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.1‐2017, 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.1‐2017, Section 4.16,
Seconds Since the Epoch). It should be noted that
implementations conforming to the System Interfaces volume of
POSIX.1‐2017 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.
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.1‐2017. 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.1‐2017 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.1‐2017 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.1‐2017, Section 4.16,
Seconds Since the Epoch, Chapter 8, Environment Variables,
Section 12.2, Utility Syntax Guidelines, sys_stat.h(0p)
The System Interfaces volume of POSIX.1‐2017, creat(3p),
futimens(3p), time(3p), utime(3p)
Portions of this text are reprinted and reproduced in electronic
form from IEEE Std 1003.1-2017, Standard for Information
Technology -- Portable Operating System Interface (POSIX), The
Open Group Base Specifications Issue 7, 2018 Edition, Copyright
(C) 2018 by the Institute of Electrical and Electronics
Engineers, Inc and The Open Group. 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.opengroup.org/unix/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 2017 TOUCH(1P)
Pages that refer to this page: qalter(1p), qselect(1p), qsub(1p)
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HTML rendering created 2024-06-26 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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