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



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

NAME
       touch - change file access and modification times

SYNOPSIS
       touch [-acm][ -r ref_file| -t time] file...

DESCRIPTION
       The  touch  utility  shall change the modification times, access times, or both of files. The modification time
       shall be equivalent to the value of the st_mtime member of the stat structure for a file, as described  in  the
       System Interfaces volume of IEEE Std 1003.1-2001; the access time shall be equivalent to the value of st_atime.

       The time used can be specified by the -t time option-argument, the corresponding time fields of the file refer-
       enced  by the -r ref_file option-argument, or the date_time operand, as specified in the following sections. If
       none of these are specified, touch shall use the current time (the value returned  by  the  equivalent  of  the
       time() function defined in the System Interfaces volume of IEEE Std 1003.1-2001).

       For  each file operand, touch shall perform actions equivalent to the following functions defined in the System
       Interfaces volume of IEEE Std 1003.1-2001:

        1. If file does not exist, a creat() function call is made with the file operand used as the path argument and
           the  value  of the bitwise-inclusive OR of S_IRUSR, S_IWUSR, S_IRGRP, S_IWGRP, S_IROTH, and S_IWOTH used as
           the mode argument.


        2. The utime() function is called with the following arguments:

            a. The file operand is used as the path argument.


            b. The utimbuf structure members actime and modtime are determined as described in the OPTIONS section.



OPTIONS
       The touch utility shall conform to the Base Definitions volume of IEEE Std 1003.1-2001, 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.

       -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 IEEE Std 1003.1-2001 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, 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 spec-
       ified.

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  IEEE Std 1003.1-2001,  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 exam-
              ple, 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  writ-
              ten 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
       IEEE Std 1003.1-2001,  Section 4.14, Seconds Since the Epoch). It should be noted that implementations conform-
       ing to the System Interfaces volume of IEEE Std 1003.1-2001 do not take leap seconds into account when  comput-
       ing  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.

EXAMPLES
       None.

RATIONALE
       The functionality of touch is described almost entirely through references to functions in  the  System  Inter-
       faces  volume  of  IEEE Std 1003.1-2001. 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  IEEE Std 1003.1-2001  and
       those  in System V and BSD systems. They are upwards-compatible for historical applications from both implemen-
       tations:

        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  recog-
           nition  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 IEEE Std 1003.1-2001 requires exit status zero if no errors occur.

FUTURE DIRECTIONS
       Applications should use the -r or -t options.

SEE ALSO
       date, the System Interfaces volume of IEEE Std 1003.1-2001, creat(), time(), utime(), the Base Definitions vol-
       ume of IEEE Std 1003.1-2001, <sys/stat.h>

COPYRIGHT
       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition, Stan-
       dard  for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifica-
       tions Issue 6, Copyright (C) 2001-2003 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 Stan-
       dard, 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 .



IEEE/The Open Group                  2003                            TOUCH(1P)