path: root/man1p/pathchk.1p

.\" Copyright (c) 2001-2003 The Open Group, All Rights Reserved 
.TH "PATHCHK" P 2003 "IEEE/The Open Group" "POSIX Programmer's Manual"
.\" pathchk 
.SH NAME
pathchk \- check pathnames
.SH SYNOPSIS
.LP
\fBpathchk\fP \fB[\fP\fB-p\fP\fB]\fP \fIpathname\fP\fB...\fP
.SH DESCRIPTION
.LP
The \fIpathchk\fP utility shall check that one or more pathnames are
valid (that is, they could be used to access or create a
file without causing syntax errors) and portable (that is, no filename
truncation results). More extensive portability checks are
provided by the \fB-p\fP option.
.LP
By default, the \fIpathchk\fP utility shall check each component of
each \fIpathname\fP operand based on the underlying file
system. A diagnostic shall be written for each \fIpathname\fP operand
that:
.IP " *" 3
Is longer than {PATH_MAX} bytes (see \fBPathname Variable Values\fP
in the Base Definitions volume of
IEEE\ Std\ 1003.1-2001, Chapter 13, Headers, \fI<limits.h>\fP)
.LP
.IP " *" 3
Contains any component longer than {NAME_MAX} bytes in its containing
directory
.LP
.IP " *" 3
Contains any component in a directory that is not searchable
.LP
.IP " *" 3
Contains any character in any component that is not valid in its containing
directory
.LP
.LP
The format of the diagnostic message is not specified, but shall indicate
the error detected and the corresponding
\fIpathname\fP operand.
.LP
It shall not be considered an error if one or more components of a
\fIpathname\fP operand do not exist as long as a file
matching the pathname specified by the missing components could be
created that does not violate any of the checks specified
above.
.SH OPTIONS
.LP
The \fIpathchk\fP utility shall conform to the Base Definitions volume
of IEEE\ Std\ 1003.1-2001, Section 12.2, Utility Syntax Guidelines.
.LP
The following option shall be supported:
.TP 7
\fB-p\fP
Instead of performing checks based on the underlying file system,
write a diagnostic for each \fIpathname\fP operand that: 
.RS
.IP " *" 3
Is longer than {_POSIX_PATH_MAX} bytes (see \fBMinimum Values\fP in
the Base Definitions volume of
IEEE\ Std\ 1003.1-2001, Chapter 13, Headers, \fI<limits.h>\fP)
.LP
.IP " *" 3
Contains any component longer than {_POSIX_NAME_MAX} bytes
.LP
.IP " *" 3
Contains any character in any component that is not in the portable
filename character set
.LP
.RE
.sp
.SH OPERANDS
.LP
The following operand shall be supported:
.TP 7
\fIpathname\fP
A pathname to be checked.
.sp
.SH STDIN
.LP
Not used.
.SH INPUT FILES
.LP
None.
.SH ENVIRONMENT VARIABLES
.LP
The following environment variables shall affect the execution of
\fIpathchk\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 
.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
All \fIpathname\fP operands passed all of the checks.
.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 \fItest\fP utility can be used to determine whether a given pathname
names an existing
file; it does not, however, give any indication of whether or not
any component of the pathname was truncated in a directory where
the _POSIX_NO_TRUNC feature is not in effect. The \fIpathchk\fP utility
does not check for file existence; it performs checks to
determine whether a pathname does exist or could be created with no
pathname component truncation.
.LP
The \fInoclobber\fP option in the shell (see the \fIset\fP special
built-in) can be used to
atomically create a file. As with all file creation semantics in the
System Interfaces volume of IEEE\ Std\ 1003.1-2001, it
guarantees atomic creation, but still depends on applications to agree
on conventions and cooperate on the use of files after they
have been created.
.SH EXAMPLES
.LP
To verify that all pathnames in an imported data interchange archive
are legitimate and unambiguous on the current system:
.sp
.RS
.nf

\fBpax -f archive | sed -e '/ == .*/s///' | xargs pathchk
if [ $? -eq 0 ]
then
    pax -r -f archive
else
    echo Investigate problems before importing files.
    exit 1
fi
\fP
.fi
.RE
.LP
To verify that all files in the current directory hierarchy could
be moved to any system conforming to the System Interfaces
volume of IEEE\ Std\ 1003.1-2001 that also supports the \fIpax\fP
utility:
.sp
.RS
.nf

\fBfind . -print | xargs pathchk -p
if [ $? -eq 0 ]
then
    pax -w -f archive .
else
    echo Portable archive cannot be created.
    exit 1
fi
\fP
.fi
.RE
.LP
To verify that a user-supplied pathname names a readable file and
that the application can create a file extending the given
path without truncation and without overwriting any existing file:
.sp
.RS
.nf

\fBcase $- in
    *C*)    reset="";;
    *)      reset="set +C"
            set -C;;
esac
test -r "$path" && pathchk "$path.out" &&
    rm "$path.out" > "$path.out"
if [ $? -ne 0 ]; then
    printf "%s: %s not found or %s.out fails \\
creation checks.\\n" $0 "$path" "$path"
    $reset    # Reset the noclobber option in case a trap
              # on EXIT depends on it.
    exit 1
fi
$reset
PROCESSING < "$path" > "$path.out"
\fP
.fi
.RE
.LP
The following assumptions are made in this example:
.IP " 1." 4
\fBPROCESSING\fP represents the code that is used by the application
to use \fB$path\fP once it is verified that
\fB$path.out\fP works as intended.
.LP
.IP " 2." 4
The state of the \fInoclobber\fP option is unknown when this code
is invoked and should be set on exit to the state it was in
when this code was invoked. (The \fBreset\fP variable is used in this
example to restore the initial state.)
.LP
.IP " 3." 4
Note the usage of:
.sp
.RS
.nf

\fBrm "$path.out" > "$path.out"
\fP
.fi
.RE
.RS
.IP " a." 4
The \fIpathchk\fP command has already verified, at this point, that
\fB$path.out\fP is not truncated.
.LP
.IP " b." 4
With the \fInoclobber\fP option set, the shell verifies that \fB$path.out\fP
does not already exist before invoking \fIrm\fP.
.LP
.IP " c." 4
If the shell succeeded in creating \fB$path.out\fP, \fIrm\fP removes
it so that the
application can create the file again in the \fBPROCESSING\fP step.
.LP
.IP " d." 4
If the \fBPROCESSING\fP step wants the file to exist already when
it is invoked, the:
.sp
.RS
.nf

\fBrm "$path.out" > "$path.out"
\fP
.fi
.RE
.LP
should be replaced with:
.sp
.RS
.nf

\fB> "$path.out"
\fP
.fi
.RE
.LP
which verifies that the file did not already exist, but leaves \fB$path.out\fP
in place for use by \fBPROCESSING\fP.
.LP
.RE
.LP
.SH RATIONALE
.LP
The \fIpathchk\fP utility was new for the ISO\ POSIX-2:1993 standard.
It, along with the \fIset\fP \fB-C\fP( \fInoclobber\fP) option added
to the shell, replaces the
\fImktemp\fP, \fIvalidfnam\fP, and \fIcreate\fP utilities that appeared
in early proposals. All of these utilities were attempts
to solve several common problems:
.IP " *" 3
Verify the validity (for several different definitions of "valid")
of a pathname supplied by a user, generated by an
application, or imported from an external source.
.LP
.IP " *" 3
Atomically create a file.
.LP
.IP " *" 3
Perform various string handling functions to generate a temporary
filename.
.LP
.LP
The \fIcreate\fP utility, included in an early proposal, provided
checking and atomic creation in a single invocation of the
utility; these are orthogonal issues and need not be grouped into
a single utility. Note that the \fInoclobber\fP option also
provides a way of creating a lock for process synchronization; since
it provides an atomic \fIcreate\fP, there is no race between
a test for existence and the following creation if it did not exist.
.LP
Having a function like \fItmpnam\fP() in the ISO\ C standard is important
in many
high-level languages. The shell programming language, however, has
built-in string manipulation facilities, making it very easy to
construct temporary filenames. The names needed obviously depend on
the application, but are frequently of a form similar to:
.sp
.RS
.nf

\fB$TMPDIR/\fP\fIapplication_abbreviation\fP\fB$$.\fP\fIsuffix\fP
.fi
.RE
.LP
In cases where there is likely to be contention for a given suffix,
a simple shell \fBfor\fP or \fBwhile\fP loop can be used
with the shell \fInoclobber\fP option to create a file without risk
of collisions, as long as applications trying to use the same
filename name space are cooperating on the use of files after they
have been created.
.SH FUTURE DIRECTIONS
.LP
None.
.SH SEE ALSO
.LP
\fIRedirection\fP , \fIset\fP , \fItest\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 .