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 (consult the correspond-
       ing 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  caus-
       ing 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,  Head-
	  ers, <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 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  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  path-
       name 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 seman-
       tics 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 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 System 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.
" $0 "$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.

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, Standard for Information Technol-
       ogy -- Portable Operating System Interface (POSIX), The Open Group Base Specifications 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 Standard, 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)