# touch

## 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_ |-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_ -_DD_ T _hh_ :_mm_ :_SS_**[**._frac_**][**_tz_**]**
    
                     or:
    
                         _YYYY_ -_MM_ -_DD_ T _hh_ :_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 **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
    


## 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
               _touch_ ed 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.
    


* * *