PATHCHK(P) POSIX Programmer's Manual PATHCHK(P)NAMEpathchk - check pathnames
SYNOPSISpathchk [-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, Head‐
ers, <limits.h>)
* Contains any component longer than {NAME_MAX} bytes in its contain‐
ing 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 indi‐
cate 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 vio‐
late 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 sys‐
tem, 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 Vari‐
ables 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 direc‐
tory where the _POSIX_NO_TRUNC feature is not in effect. The pathchk
utility does not check for file existence; it performs checks to deter‐
mine 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 conven‐
tions 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.\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 $path.out, rm removes it so
that the application can create the file again in the PROCESS‐
ING step.
d. If the PROCESSING step wants the file to exist already when it
is invoked, the:
rm "$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 pro‐
posals. 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 con‐
struct 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 applica‐
tions 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 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 original Standard can be obtained online
at http://www.opengroup.org/unix/online.html .
IEEE/The Open Group 2003 PATHCHK(P)
