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Linux 2.6 - man page for pathchk (linux section 1posix)

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

       pathchk - check pathnames

       pathchk [-p] pathname...

       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

       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

	* 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 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.

       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 diagnos-
	      tic for each pathname operand that:

	       * Is longer than {_POSIX_PATH_MAX} bytes (see Minimum Values in the  Base  Defini-
		 tions 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

       The following operand shall be supported:

	      A pathname to be checked.

       Not used.


       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, Inter-
	      nationalization 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 interna-
	      tionalization variables.

	      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 argu-

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

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


       Not used.

       The standard error shall be used only for diagnostic messages.



       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 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.

       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 ]
		  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 IEEE Std 1003.1-2001 that also supports  the
       pax utility:

	      find . -print | xargs pathchk -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

	    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  applica-
	       tion 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.

       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 sup-
	  plied 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 lan-
       guages.	The shell programming language, however, has built-in string manipulation facili-
       ties, 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 cooper-
       ating on the use of files after they have been created.


       Redirection , set , test

       Portions of this text are reprinted and	reproduced  in	electronic  form  from	IEEE  Std
       1003.1,	2003  Edition,	Standard  for Information Technology -- 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 orig-
       inal Standard can be obtained online at http://www.opengroup.org/unix/online.html .

IEEE/The Open Group			       2003				       PATHCHK(P)

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