Usage: touch [OPTION]... FILE...
Update the access and modification times of each FILE to the current time.

A FILE argument that does not exist is created empty, unless -c or -h
is supplied.

A FILE argument string of - is handled specially and causes touch to
change the times of the file associated with standard output.

Mandatory arguments to long options are mandatory for short options too.

  -a                     change only the access time

  -c, --no-create        do not create any files

  -d, --date=STRING      parse STRING and use it instead of current time

  -f                     (ignored)

  -h, --no-dereference   affect each symbolic link instead of any referenced
                         file (useful only on systems that can change the
                         timestamps of a symlink)

  -m                     change only the modification time

  -r, --reference=FILE   use this file's times instead of current time

  -t STAMP               use [[CC]YY]MMDDhhmm[.ss] instead of current time
      --time=WORD        change the specified time:
                           WORD is access, atime, or use: equivalent to -a
                           WORD is modify or mtime: equivalent to -m
      --help     display this help and exit
      --version  output version information and exit

Note that the -d and -t options accept different time-date formats.

GNU coreutils online help: <http://www.gnu.org/software/coreutils/>
Full documentation at: <http://www.gnu.org/software/coreutils/touch>
or available locally via: info '(coreutils) touch invocation'