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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 dif-
       fer (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] 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 corre-
       sponding 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 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  prece-
              dence 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  exam-
              ple, 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 writ-
              ten 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,  how-
       ever,  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  per-
       forms  checks to determine whether a pathname does exist or could be created with no pathname component trunca-
       tion.

       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 cur-
       rent system:


              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 Sys-
       tem Interfaces 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 ini-
           tial 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, gener-
          ated 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 pro-
       gramming language, however, has built-in string manipulation facilities, making it very easy to construct  tem-
       porary  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 try-
       ing to use the same filename name space are cooperating on the use of files after they have been created.

FUTURE DIRECTIONS
       None.

SEE ALSO
       Redirection, set, test

COPYRIGHT
       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition, Stan-
       dard  for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifica-
       tions 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 Stan-
       dard, 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 .



IEEE/The Open Group                  2003                          PATHCHK(1P)