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       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

       pathchk — check pathnames

SYNOPSIS

       pathchk [−p] [−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 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.1‐2008, <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 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 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  matching  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 POSIX.1‐2008, 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.1‐2008, <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

       −P        Write a diagnostic for each pathname operand that:

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

                  *  Is empty

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  POSIX.1‐2008,  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).

       LC_MESSAGES
                 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.

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 pathname 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 POSIX.1‐2008, 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 together.

EXAMPLES

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 ]
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 Interfaces volume of POSIX.1‐2008 that also supports the pax utility:

find . −exec pathchk −p −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 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> character as the first character
in a component of the pathname, or for an empty pathname operand.

FUTURE DIRECTIONS

       None.

COPYRIGHT

       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2013 Edition,
       Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open  Group  Base
       Specifications  Issue 7, Copyright (C) 2013 by the Institute of Electrical and Electronics Engineers, Inc
       and The Open Group.  (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) 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.unix.org/online.html .

       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
       https://www.kernel.org/doc/man-pages/reporting_bugs.html .