STANDARD INPUT

None.

INPUT FILES

None.

ENVIRONMENT VARIABLES

The following environment variables shall affect the execution of pathchk:

LANG

This variable shall determine the locale to use for the locale categories when both LC_ALL and the corresponding environment variable (beginning with LC_ ) do not specify a locale. See 2.6.

LC_ALL

This variable shall determine the locale to be used to override any values for locale categories specified by the settings of LANG or any environment variables beginning with LC_.

LC_CTYPE

This variable shall determine the locale for the interpretation of sequences of bytes of text data as characters (e.g., single- versus multibyte characters in arguments).

LC_MESSAGES

This variable shall determine the language in which messages should be written.

ASYNCHRONOUS EVENTS

Default.

STANDARD OUTPUT

None.

STANDARD ERROR

Used only for diagnostic messages.

OUTPUT FILES

None.

EXAMPLES

To verify that all pathnames in an imported data interchange archive are legitimate and unambiguous on the current system: pax -f archive | xargs pathchk if [ $? -eq 0 ] then pax -r -f archive else echo Investigate problems before importing files. exit fi To verify that all files in the current directory hierarchy could be moved to any POSIX. 1 {8} conforming system 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 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 fi $reset PROCESSING < "$path" > "$path.out"

The following assumptions are made in this example:

1. PROCESSING represents the code that will be used by the application to use $path once it is verified that $path.out will work as intended.
2. The state of the noclobber option is unknown when this code is invoked and should be set on exit to the state it was in when this code was invoked. (The reset variable is used in this example to restore the initial state.)
3. Note the usage of rm "$path.out" > "$path.out": (a) The pathchk command has already verified, at this point, that $path.out will not be truncated. (b) With the noclobber option set, the shell will verify that $path.out does not already exist before invoking rm. (c) If the shell succeeded in creating $path.out, rm will remove it so that the application can create the file again in the PROCESSING step. (d) If the PROCESSING step wants the file to already exist when it is invoked, the

rm "$path.out" > "$path.out" should be replaced with > "$path.out" which will verify that the file did not already exist, but leave $path.out in place for use by PROCESSING.

HISTORY OF DECISIONS MADE

The pathchk utility is new, commissioned for this standard. It, along with the set −C (noclobber) option added to the shell, replaces the mktemp, validfnam, and create utilities that appeared in earlier drafts. All of these utilities were attempts to solve a few 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, and
• Perform various string handling functions to generate a temporary file name.

The test utility (see test(1) ) can be used to determine if a given pathname names an existing file; it will 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 (see Execution-Time Symbolic Constants for Portability Specification in POSIX. 1 {8} 2.9.4) is not in effect. The pathchk utility provided here does not check for file existence; it performs checks to determine if a pathname does exist or could be created with no pathname component truncation. The noclobber option added to the shell (see set(1) ) can be used to atomically create a file. As with all file creation semantics in POSIX. 1 {8}, 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. The create utility, included in one earlier draft, 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 C Standard {7} 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 file names. 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 filename

namespace are cooperating on the use of files after they have been created.