touch(1p) - phpMan

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 differ (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 cor-
       responding  time  fields  of  the  file  referenced  by the -r ref_file
       option-argument, or the date_time operand, as specified in the  follow-
       ing  sections. If none of these are specified, touch shall use the cur-
       rent 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  bit-
           wise-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  sec-
       onds.  If SS is 60, and the resulting time, as affected by the TZ envi-
       ronment 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
              IEEE Std 1003.1-2001, Section  8.2,  Internationalization  Vari-
              ables  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 IEEE Std 1003.1-2001, Section 4.14, Sec-
       onds 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 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 sec-
       onds 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  deci-
       mal 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 refer-
       ences   to   functions   in   the   System   Interfaces    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  sys-
       tems. 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 con-
           forming 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  speci-
           fied.  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  capa-
       bility.  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  dif-
       ferent 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 volume  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, Standard for Information Technology
       --  Portable  Operating  System  Interface (POSIX), The Open Group Base
       Specifications 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 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 .

IEEE/The Open Group                  2003                            TOUCH(1P)