path: root/man1p/touch.1p

.\" Copyright (c) 2001-2003 The Open Group, All Rights Reserved 
.TH "TOUCH" P 2003 "IEEE/The Open Group" "POSIX Programmer's Manual"
.\" touch 
.SH NAME
touch \- change file access and modification times
.SH SYNOPSIS
.LP
\fBtouch\fP \fB[\fP\fB-acm\fP\fB][\fP \fB-r\fP \fIref_file\fP\fB|
-t\fP \fItime\fP\fB]\fP
\fIfile\fP\fB...\fP
.SH DESCRIPTION
.LP
The \fItouch\fP utility shall change the modification times, access
times, or both of files. The modification time shall be
equivalent to the value of the \fIst_mtime\fP member of the \fBstat\fP
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 \fIst_atime\fP.
.LP
The time used can be specified by the \fB-t\fP \fItime\fP option-argument,
the corresponding time fields of the file
referenced by the \fB-r\fP \fIref_file\fP option-argument, or the
\fIdate_time\fP operand, as specified in the following
sections. If none of these are specified, \fItouch\fP shall use the
current time (the value returned by the equivalent of the \fItime\fP()
function defined in the System Interfaces volume of
IEEE\ Std\ 1003.1-2001).
.LP
For each \fIfile\fP operand, \fItouch\fP shall perform actions equivalent
to the following functions defined in the System
Interfaces volume of IEEE\ Std\ 1003.1-2001:
.IP " 1." 4
If \fIfile\fP does not exist, a \fIcreat\fP() function call is made
with the \fIfile\fP
operand used as the \fIpath\fP 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 \fImode\fP argument.
.LP
.IP " 2." 4
The \fIutime\fP() function is called with the following arguments:
.RS
.IP " a." 4
The \fIfile\fP operand is used as the \fIpath\fP argument.
.LP
.IP " b." 4
The \fButimbuf\fP structure members \fIactime\fP and \fImodtime\fP
are determined as described in the OPTIONS section.
.LP
.RE
.LP
.SH OPTIONS
.LP
The \fItouch\fP utility shall conform to the Base Definitions volume
of IEEE\ Std\ 1003.1-2001, Section 12.2, Utility Syntax Guidelines.
.LP
The following options shall be supported:
.TP 7
\fB-a\fP
Change the access time of \fIfile\fP. Do not change the modification
time unless \fB-m\fP is also specified.
.TP 7
\fB-c\fP
Do not create a specified \fIfile\fP if it does not exist. Do not
write any diagnostic messages concerning this
condition.
.TP 7
\fB-m\fP
Change the modification time of \fIfile\fP. Do not change the access
time unless \fB-a\fP is also specified.
.TP 7
\fB-r\ \fP \fIref_file\fP
Use the corresponding time of the file named by the pathname \fIref_file\fP
instead of the current time.
.TP 7
\fB-t\ \fP \fItime\fP
Use the specified \fItime\fP instead of the current time. The option-argument
shall be a decimal number of the form: 
.sp
.RS
.nf

\fB[[\fP\fICC\fP\fB]\fP\fIYY\fP\fB]\fP\fIMMDDhhmm\fP\fB[\fP\fB.\fP\fISS\fP\fB]\fP
.fi
.RE
.LP
where each two digits represents the following:
.TP 7
\fIMM\fP
.RS
The month of the year [01,12].
.RE
.TP 7
\fIDD\fP
.RS
The day of the month [01,31].
.RE
.TP 7
\fIhh\fP
.RS
The hour of the day [00,23].
.RE
.TP 7
\fImm\fP
.RS
The minute of the hour [00,59].
.RE
.TP 7
\fICC\fP
.RS
The first two digits of the year (the century).
.RE
.TP 7
\fIYY\fP
.RS
The second two digits of the year.
.RE
.TP 7
\fISS\fP
.RS
The second of the minute [00,60].
.RE
.sp
.LP
Both \fICC\fP and \fIYY\fP shall be optional. If neither is given,
the current year shall be assumed. If \fIYY\fP is
specified, but \fICC\fP is not, \fICC\fP shall be derived as follows:
.TS C
center; l l.
\fBIf \fIYY\fP is:\fP	\fB\fICC\fP becomes:\fP
[69,99]	19
[00,68]	20
.TE
.TP 7
\fBNote:\fP
.RS
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.)
.RE
.sp
.LP
The resulting time shall be affected by the value of the \fITZ\fP
environment variable. If the resulting time value precedes
the Epoch, \fItouch\fP 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 \fBsigned int\fP
as a time holder.
.LP
The range for \fISS\fP is [00,60] rather than [00,59] because of leap
seconds. If \fISS\fP is 60, and the resulting time, as
affected by the \fITZ\fP environment variable, does not refer to a
leap second, the resulting time shall be one second after a
time where \fISS\fP is 59. If \fISS\fP is not given a value, it is
assumed to be zero.
.sp
.LP
If neither the \fB-a\fP nor \fB-m\fP options were specified, \fItouch\fP
shall behave as if both the \fB-a\fP and \fB-m\fP
options were specified.
.SH OPERANDS
.LP
The following operands shall be supported:
.TP 7
\fIfile\fP
A pathname of a file whose times shall be modified.
.sp
.SH STDIN
.LP
Not used.
.SH INPUT FILES
.LP
None.
.SH ENVIRONMENT VARIABLES
.LP
The following environment variables shall affect the execution of
\fItouch\fP:
.TP 7
\fILANG\fP
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.)
.TP 7
\fILC_ALL\fP
If set to a non-empty string value, override the values of all the
other internationalization variables.
.TP 7
\fILC_CTYPE\fP
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).
.TP 7
\fILC_MESSAGES\fP
Determine the locale that should be used to affect the format and
contents of diagnostic messages written to standard
error.
.TP 7
\fINLSPATH\fP
Determine the location of message catalogs for the processing of \fILC_MESSAGES
\&.\fP 
.TP 7
\fITZ\fP
Determine the timezone to be used for interpreting the \fItime\fP
option-argument. If \fITZ\fP is unset or null, an
unspecified default timezone shall be used.
.sp
.SH ASYNCHRONOUS EVENTS
.LP
Default.
.SH STDOUT
.LP
Not used.
.SH STDERR
.LP
The standard error shall be used only for diagnostic messages.
.SH OUTPUT FILES
.LP
None.
.SH EXTENDED DESCRIPTION
.LP
None.
.SH EXIT STATUS
.LP
The following exit values shall be returned:
.TP 7
\ 0
The utility executed successfully and all requested changes were made.
.TP 7
>0
An error occurred.
.sp
.SH CONSEQUENCES OF ERRORS
.LP
Default.
.LP
\fIThe following sections are informative.\fP
.SH APPLICATION USAGE
.LP
The interpretation of time is taken to be \fIseconds since the Epoch\fP
(see the Base Definitions volume of
IEEE\ Std\ 1003.1-2001, Section 4.14, Seconds Since the Epoch). It
should be noted that implementations conforming 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
\fISS\fP=60 is used, the resulting time always refers to 1 plus
\fIseconds since the Epoch\fP for a time when \fISS\fP=59.
.LP
Although the \fB-t\fP \fItime\fP 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 \fITZ\fP when
\fItouch\fP is run, there is never more than a few valid hours in
1969 and there need not be any valid times in 1969.
.LP
One ambiguous situation occurs if \fB-t\fP \fItime\fP is not specified,
\fB-r\fP \fIref_file\fP is not specified, and the
first operand is an eight or ten-digit decimal number. A portable
script can avoid this problem by using:
.sp
.RS
.nf

\fBtouch -- file
\fP
.fi
.RE
.LP
or:
.sp
.RS
.nf

\fBtouch ./file
\fP
.fi
.RE
.LP
in this case.
.SH EXAMPLES
.LP
None.
.SH RATIONALE
.LP
The functionality of \fItouch\fP is described almost entirely through
references 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.
.LP
There are some significant differences between the \fItouch\fP 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 implementations:
.IP " 1." 4
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 \fItime\fP value is allowed; files may only be \fItouch\fPed
to the current time. The \fB-t\fP \fItime\fP construct
solves these problems for future conforming applications (note that
the \fB-t\fP option is not historical practice).
.LP
.IP " 2." 4
The inclusion of the century digits, \fICC\fP, is also new. Note that
a ten-digit \fItime\fP value is treated as if \fIYY\fP,
and not \fICC\fP, 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 \fBsigned int\fP as a time holder.
.LP
.LP
The \fB-r\fP option was added because several comments requested this
capability. This option was named \fB-f\fP in an early
proposal, but was changed because the \fB-f\fP option is used in the
BSD version of \fItouch\fP with a different meaning.
.LP
At least one historical implementation of \fItouch\fP incremented
the exit code if \fB-c\fP was specified and the file did not
exist. This volume of IEEE\ Std\ 1003.1-2001 requires exit status
zero if no errors occur.
.SH FUTURE DIRECTIONS
.LP
Applications should use the \fB-r\fP or \fB-t\fP options.
.SH SEE ALSO
.LP
\fIdate\fP , the System Interfaces volume of IEEE\ Std\ 1003.1-2001,
\fIcreat\fP(), \fItime\fP(), \fIutime\fP(), the Base Definitions volume
of IEEE\ Std\ 1003.1-2001, \fI<sys/stat.h>\fP
.SH 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 .