TOUCH(1)                   POSIX Programmer's Manual                  TOUCH(1)



PROLOG
       This manual page is part of the POSIX Programmer's Manual.  The OS
       implementation of this interface may differ (consult the corresponding
       OS manual page for details of OS behavior), or the interface may not be
       implemented on OS.

NAME
       touch -- change file access and modification times

SYNOPSIS
       touch [[-acm]] [[-r ref__file|-t time|-d date__time]] file...

DESCRIPTION
       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.

OPTIONS
       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-_D_DT_h_h:mm:SS[[.frac]][[tz]]

                 or:


                     YYYY-MM-_D_DT_h_h: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.

OPERANDS
       The following operands shall be supported:

       file      A pathname of a file whose times shall be modified.

STDIN
       Not used.

INPUT FILES
       None.

ENVIRONMENT VARIABLES
       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.

ASYNCHRONOUS EVENTS
       Default.

STDOUT
       Not used.

STDERR
       The standard error shall be used only for diagnostic messages.

OUTPUT FILES
       None.

EXTENDED DESCRIPTION
       None.

EXIT STATUS
       The following exit values shall be returned:

        0    The utility executed successfully and all requested changes were
             made.

       >0    An error occurred.

CONSEQUENCES OF ERRORS
       Default.

       The following sections are informative.

APPLICATION USAGE
       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.

EXAMPLES
       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 eebbbb99; 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

RATIONALE
       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>.

FUTURE DIRECTIONS
       None.

SEE ALSO
       date

       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>

       The System Interfaces volume of POSIX.1-2017, creat(), futimens(),
       time(), utime()

COPYRIGHT
       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(1)
