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PATHCHK(1P) POSIX Programmer's Manual PATHCHK(1P)

PROLOG
This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may differ (con-
sult the corresponding Linux manual page for details of Linux behavior), or the interface may not be implemented on
Linux.

NAME
pathchk - check pathnames

SYNOPSIS
pathchk [-p] pathname...

DESCRIPTION
The pathchk 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 -p option.

By default, the pathchk utility shall check each component of each pathname operand based on the underlying file system.
A diagnostic shall be written for each pathname operand that:

* Is longer than {PATH_MAX} bytes (see Pathname Variable Values in the Base Definitions volume of IEEE Std 1003.1-2001,
Chapter 13, Headers, <limits.h>)

* Contains any component longer than {NAME_MAX} bytes in its containing directory

* Contains any component in a directory that is not searchable

* Contains any character in any component that is not valid in its containing directory

The format of the diagnostic message is not specified, but shall indicate the error detected and the corresponding path-
name operand.

It shall not be considered an error if one or more components of a pathname operand do not exist as long as a file match-
ing the pathname specified by the missing components could be created that does not violate any of the checks specified
above.

OPTIONS
The pathchk utility shall conform to the Base Definitions volume of IEEE Std 1003.1-2001, Section 12.2, Utility Syntax
Guidelines.

The following option shall be supported:

-p Instead of performing checks based on the underlying file system, write a diagnostic for each pathname operand
that:

* Is longer than {_POSIX_PATH_MAX} bytes (see Minimum Values in the Base Definitions volume of
IEEE Std 1003.1-2001, Chapter 13, Headers, <limits.h>)

* Contains any component longer than {_POSIX_NAME_MAX} bytes

* Contains any character in any component that is not in the portable filename character set

OPERANDS
The following operand shall be supported:

pathname
A pathname to be checked.

STDIN
Not used.

INPUT FILES
None.

ENVIRONMENT VARIABLES
The following environment variables shall affect the execution of pathchk:

LANG 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 international-
ization 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 stan-
dard error.

NLSPATH
Determine the location of message catalogs for the processing of LC_MESSAGES .

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 All pathname operands passed all of the checks.

>0 An error occurred.

CONSEQUENCES OF ERRORS
Default.

The following sections are informative.

APPLICATION USAGE
The test 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 pathchk utility does not check for file existence; it performs checks to determine whether a path-
name does exist or could be created with no pathname component truncation.

The noclobber option in the shell (see the set 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.

EXAMPLES
To verify that all pathnames in an imported data interchange archive are legitimate and unambiguous on the current sys-
tem:

pax -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

To verify that all files in the current directory hierarchy could be moved to any system conforming to the System Inter-
faces volume of IEEE Std 1003.1-2001 that also supports the pax utility:

find . -print | xargs pathchk -p
if [ $? -eq 0 ]
then
pax -w -f archive .
else
echo Portable archive cannot be created.
exit 1
fi

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:

case $- in
*C*) reset="";;
*) reset="set +C"
set -C;;
esac
test -r "$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"

The following assumptions are made in this example:

1. PROCESSING represents the code that is used by the application to use $path once it is verified that $path.out works
as intended.

2. The state of the noclobber 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 reset variable is used in this example to restore the initial state.)

3. Note the usage of:

rm "$path.out" > "$path.out"

a. The pathchk command has already verified, at this point, that $path.out is not truncated.

b. With the noclobber option set, the shell verifies that $path.out does not already exist before invoking rm.

c. If the shell succeeded in creating $path.out, rm removes it so that the application can create the file again in
the PROCESSING step.

d. If the PROCESSING step wants the file to exist already when it is invoked, the:

rm "$path.out" > "$path.out"

should be replaced with:

> "$path.out"

which verifies that the file did not already exist, but leaves $path.out in place for use by PROCESSING.

RATIONALE
The pathchk utility was new for the ISO POSIX-2:1993 standard. It, along with the set -C( noclobber) option added to the
shell, replaces the mktemp, validfnam, and create utilities that appeared in early proposals. All of these utilities were
attempts to solve several common problems:

* 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.

* Atomically create a file.

* Perform various string handling functions to generate a temporary filename.

The create 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 noclobber option also
provides a way of creating a lock for process synchronization; since it provides an atomic create, there is no race
between a test for existence and the following creation if it did not exist.

Having a function like tmpnam() 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:

$TMPDIR/application_abbreviation$$.suffix

In cases where there is likely to be contention for a given suffix, a simple shell for or while loop can be used with the
shell noclobber option to create a file without risk of collisions, as long as applications trying to use the same file-
name name space are cooperating on the use of files after they have been created.

FUTURE DIRECTIONS
None.