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\"     @(#)touch.1      8.3 (Berkeley) 4/28/95
\"
Dd February 10, 2024
Dt TOUCH 1
Os
Sh NAME
Nm touch
Nd change file access and modification times
Sh SYNOPSIS
Nm
Op Fl acDfhm
Op Fl d Ar posix-datetime|human-datetime
Op Fl Fl \|date Ar posix-datetime|human-datetime
Op Fl R Ar ref-file
Op Fl r Ar ref-file
Op Fl Fl \|reference Ar ref-file
Op Fl t Ar datetime
Ar file ...
Sh DESCRIPTION
The
Nm
utility changes either or both of the access and modification times of the
Ar file Ns s
to the time specified by the options, described below,
or to the current time of day, if none of those options is present.
If the file doesn't exist, it is first created with default permissions.
Pp
The following options are available:
Bl -tag -compact -width Fl
Pp
It Fl a
Change the access time of the
Ar file .
The modification time of the
Ar file
is not changed unless the
Fl m
flag is also specified.
Pp
It Fl c
Do not create the
Ar file
if it does not exist.
The
Nm
utility does not treat this as an error.
No error messages are displayed and the exit value is not affected.
Pp
It Fl D
Do not attempt to adjust a
Ar file Ns 's
times if they are already set to the values specified.
Pp
It Fl d Ar posix-datetime
It Fl d Ar human-datetime
It Fl Fl \|date Ar posix-datetime
It Fl Fl \|date Ar human-datetime
Attempt to parse the arg
Ar posix-datetime
as a POSIX time string
Dq CCYY\-MM\-DDThh:mm:ss[.frac][Z]
where the minus (or hyphen)
Pq Sq \&\-
and colon
Pq Sq \&:
characters are literals, and:
Bl -bullet -compact
It
Cm CCYY
represents a 4 (or more) digit year number,
It
Cm MM
represents a 2 digit month number (1\-12),
It
Cm DD
represents a 2 digit day of the month (1\-31),
It
Cm T
represents either the character
Sq T
or a single space character (in which case the
space, at least, may need to be quoted to the shell to
avoid the arg being split into two words),
It
Cm hh
represents a 2 digit hour of the day (00\-23),
It
Cm mm
represents a 2 digit minute of the hour (00\-59),
It
Cm ss
represents a 2 digit second of the minute (00\-60)
where 60 indicates the occurrence of a leap second,
which POSIX systems ignore, resulting in the following
second being generated instead (:00 of the next minute),
It
Cm .frac
represents optional factional seconds, where the
Sq \&.
can be a period
Pq Sq \&.
or a comma
Pq Sq \&,
and
Cm frac
gives one or more digits, interpreted as if
in a floating-point representation of the seconds,
so
Dq \&.3
represents three tenths of a second, and
Dq \&,17
represents seventeen hundredths of a second, etc.
Note that if the period or comma is given, there
must be at least one following digit.
If no fraction of a second is to be specified,
also omit the period (or comma).
If omitted, the fractional seconds are set to 0,
so specifying
Dq \&.0
or
Dq \&,0
is identical to omitting the
Cm \&.frac
field entirely,
It
Cm Z
represents an optional literal
Sq Z
character, indicating the the time given is to
be considered as a Co-ordinated Universal Time (UTC) value.
If omitted, the time is considered as being in the local
timezone, as specified by the
Ev TZ
environment variable.
El
Pp
Note that parsing of this string is quite strict.
If successfully parsed, the time to set will be that
specified by this string.
Pp
If the attempt to parse the string as a
Ar posix-datetime
fails, then
Nm
will attempt to parse it as a
Ar human-datetime
using the human datetime parser
Xr parsedate 3 ,
and use the result as the time to set.
Pp
It Fl f
This flag has no effect; it is accepted for compatibility reasons.
Pp
It Fl h
If a
Ar file
is a symbolic link, the access and/or modification time of the link is changed.
This option implies
Fl c .
Pp
It Fl m
Change the modification time of the
Ar file .
The access time of the
Ar file
is not changed unless the
Fl a
flag is also specified.
Pp
It Fl R Ar ref-file
It Fl r Ar ref-file
It Fl Fl \|reference Ar ref-file
Use the access and modification times,
as appropriate for the operation being performed,
from
Ar ref-file
instead of the current time of day.
If the
Ar ref-file
is a symbolic link,
then if the
Fl R
form of this option was used,
the times are taken from the symbolic link itself,
otherwise
the times are taken from the file referenced by it.
If
Ar ref-file
is not a symbolic link, all three forms are identical.
Pp
It Fl t Ar datetime
Change the access and modification times of the
Ar file Ns Pq s
to the specified
Ar datetime.
The argument
Ar datetime
should be in the form
Dq [[CC]YY]MMDDhhmm[.ss]
where each pair of letters represents exactly 2 decimal digits,
with the following interpretations:
Pp
Bl -tag -width Ds -compact -offset indent
It Ar CC
The first two digits of the year (the century).
It Ar YY
The second two digits of the year.
If
Dq YY
is specified, but
Dq CC
is not, a value for
Dq YY
between 69 and 99 (inclusive) results in a
Dq CC
value of 19.
Otherwise, a
Dq CC
value of 20 is used.
It Ar MM
The month of the year, from 1 to 12.
It Ar DD
The day of the month, from 1 to 31.
It Ar hh
The hour of the day, from 0 to 23.
It Ar mm
The minute of the hour, from 0 to 59.
It Ar ss
The second of the minute, from 0 to 60 (permitting leap seconds).
If
Ar ss
is 60 and the resulting time,
as affected by the
Ev TZ
environment variable,
does not refer to a leap second,
the resulting time is one second after a time where
Ar ss
is 59.
If
Ar ss
is not given a value, it is assumed to be zero, and the
preceding period
Pq Sq \&.
must be omitted.
El
Pp
If the
Dq CC
and
Dq YY
letter pairs are not specified, the values default to the current
year.
If the
Dq ss
letter pair
Pq and the preceding period
is not specified, the value defaults to 0.
As an extension to the standard, any of the
Dq MM ,
Dq DD ,
and
Dq hh
fields may also be omitted, defaulting to the current
time of day,
but once any one of these letter pairs is given, all
the following ones
Pq except Dq \&.ss
are required.
Fields must always be specified as 2 digits, even when
the value is less than 10.
Leading zeroes do not cause the value to be treated as octal,
all conversions use decimal numbers.
El
Pp
The
Fl d ,
Fl R ,
Fl r ,
and
Fl t
options are (nominally) mutually exclusive.
If more than one of these options is present,
each will be evaluated, and may cause an error,
then the result from the last one specified is used.
Pp
The options which specify any part of the time
Pq Fl d , Fl R, Fl r , Fl t
apply to both the access and modification times
(with
Fl r
and
Fl R
obtaining those values independently from the
Ar ref-file ) ,
though which is actually applied depends upon
the
Fl a
and
Fl m
options.
Sh ENVIRONMENT
Bl -tag -width -iTZ
It Ev TZ
The time zone to be used for interpreting the
Ar datetime
argument of the
Fl t
option, and the default zone for the
Ar posix-datetime
or
Ar human-datetime
argument of the
Fl d
option.
El
Sh EXAMPLES
Dl touch -h -r path path
Pp
If
Ar path
is a symbolic link, this will set the symbolic link's
access and modify timestamps identical to those of the
file to which it refers.
If
Ar path
is not a symbolic link,
this will simply update the
Dq inode changed
time
Pq Dq ctime
of the
Ar path
file to the current time of day.
Pp
Dl touch -Dh -d human-datetime -t CCYYMMDDhhmm.ss -R file file
Pp
Provided
Ar file
exists, this parses the
Ar human-datetime
and
Ar CCYYMMDDhhmm.ss
arguments,
verifying that they would be suitable for use with
Nm ,
then does nothing, as the final time specification
Pq Fl R
specifies to take the times from
Ar file
and apply them to
Ar file
itself, changing nothing, which the
Fl D
option then prevents from actually occurring.
That is, this merely tests that the
Ar human-datetime
and
Ar datetime
arguments to
Fl d
and
Fl t
respectively are valid, and could be used to specify a time.
Use of both
Fl h
and
Fl R
means this works if
Ar file
is a symbolic link,
even one which does not reference an existing file,
as well as if it is some other file type.
Use of
Fl R
requires that
Ar file
exists,
though if it does not, and an error is generated for that reason,
the
Fl d
and
Fl t
arguments would have already been successfully processed.
Pp
Dl touch -m -d '-1 day' somefile
Pp
Set the modify time for
Ar somefile
to one day (24 hours) earlier than the current time.
Sh EXIT STATUS
Ex -std
Sh COMPATIBILITY
The obsolescent form of
Nm ,
where a time format is specified as the first argument, is supported.
When none of the time setting options is specified,
there are at least two arguments,
and the first argument is a string of digits
which is either eight or ten characters in length,
the first argument is interpreted as a time specification of the form
Dq MMDDhhmm[YY]
and applied to the remaining arguments interpreted as path names.
Pp
The
Dq MM ,
Dq DD ,
Dq hh
and
Dq mm
letter pairs are treated as their counterparts specified to the
Fl t
option, except that none of these are optional.
If the
Dq YY
letter pair is present,
it is interpret the same as
Dq YY
in the
Fl t
option with no
Dq CC
specified, however here it appears last, rather than first.
There are no equivalents to the
Dq CC
or
Dq ss
fields of
Fl t
and the fractional seconds field is always set to zero.
Sh SEE ALSO
Xr utimes 2 ,
Xr parsedate 3
Sh "FUTURE PLANNING"
Sometime in the middle of the 21st century, the default
Dq CC
used in formats where that information is not present, or
where those digits are not given, will be altered to
make low year numbers represent the 22nd century, and high
years the 21st century.
The boundary between low and high is also expected to change.
To avoid issues, always use formats which include the
Dq CC
field, and always use it when
Dq YY
is given.
Sh STANDARDS
The
Nm
utility is expected to be a superset of the
St -p1003.2
and
St -p1003.1-2008
specifications.
Sh HISTORY
A
Nm
utility appeared in
At v7 .

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