Ubuntu Manpage: This manual page is part of the POSIX Programmer's Manual. The Linux implementation of

Provided by: manpages-posix_2013a-1_all

PROLOG

       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 .