pathchk(1p) — Linux manual page


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

PROLOG         top

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

NAME         top

       pathchk — check pathnames

SYNOPSIS         top

       pathchk [-p] [-P] pathname...

DESCRIPTION         top

       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 and -P options.

       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 POSIX.1‐2017, limits.h(0p))

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

        *  Contains any component in a directory that is not searchable

        *  Contains any byte sequence 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 pathname

       It shall not be considered an error if one or more components of
       a pathname 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.

OPTIONS         top

       The pathchk utility shall conform to the Base Definitions volume
       of POSIX.1‐2017, 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
                     POSIX.1‐2017, limits.h(0p))

                  *  Contains any component longer than
                     {_POSIX_NAME_MAX} bytes

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

       -P        Write a diagnostic for each pathname operand that:

                  *  Contains a component whose first character is the
                     <hyphen-minus> character

                  *  Is empty

OPERANDS         top

       The following operand shall be supported:

       pathname  A pathname to be checked.

STDIN         top

       Not used.

INPUT FILES         top



       The following environment variables shall affect the execution of

       LANG      Provide a default value for the internationalization
                 variables that are unset or null. (See the Base
                 Definitions volume of POSIX.1‐2017, Section 8.2,
                 Internationalization Variables the precedence of
                 internationalization 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).

                 Determine the locale that should be used to affect the
                 format and contents of diagnostic messages written to
                 standard error.

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



STDOUT         top

       Not used.

STDERR         top

       The standard error shall be used only for diagnostic messages.

OUTPUT FILES         top




EXIT STATUS         top

       The following exit values shall be returned:

        0    All pathname operands passed all of the checks.

       >0    An error occurred.



       The following sections are informative.


       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 pathname does exist or
       could be created with no pathname component truncation.

       The noclobber option in the shell (see the set(1p) special built-
       in) can be used to atomically create a file. As with all file
       creation semantics in the System Interfaces volume of
       POSIX.1‐2017, 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.

       To verify that a pathname meets the requirements of filename
       portability, applications should use both the -p and -P options

EXAMPLES         top

       To verify that all pathnames in an imported data interchange
       archive are legitimate and unambiguous on the current system:

           # This example assumes that no pathnames in the archive
           # contain <newline> characters.
           pax -f archive | sed -e 's/[^[:alnum:]]/\\&/g' | xargs pathchk --
           if [ $? -eq 0 ]
               pax -r -f archive
               echo Investigate problems before importing files.
               exit 1

       To verify that all files in the current directory hierarchy could
       be moved to any system conforming to the System Interfaces volume
       of POSIX.1‐2017 that also supports the pax utility:

           find . -exec pathchk -p -P {} +
           if [ $? -eq 0 ]
               pax -w -f ../archive .
               echo Portable archive cannot be created.
               exit 1

       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 $- in
               *C*)    reset="";;
               *)      reset="set +C"
                       set -C;;
           test -r "$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"
               $reset    # Reset the noclobber option in case a trap
                         # on EXIT depends on it.
               exit 1
           PROCESSING < "$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         top

       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:


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

       For historical purposes, -p does not check for the use of the
       <hyphen-minus> character as the first character in a component of
       the pathname, or for an empty pathname operand.



SEE ALSO         top

       Section 2.7, Redirection, set(1p), test(1p)

       The Base Definitions volume of POSIX.1‐2017, Chapter 8,
       Environment Variables, Section 12.2, Utility Syntax Guidelines,

COPYRIGHT         top

       Portions of this text are reprinted and reproduced in electronic
       form from IEEE Std 1003.1-2017, Standard for Information
       Technology -- Portable Operating System Interface (POSIX), The
       Open Group Base Specifications Issue 7, 2018 Edition, Copyright
       (C) 2018 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 .

       Any typographical or formatting errors that appear in this page
       are most likely to have been introduced during the conversion of
       the source files to man page format. To report such errors, see .

IEEE/The Open Group               2017                       PATHCHK(1P)