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PROLOG | NAME | SYNOPSIS | DESCRIPTION | OPTIONS | OPERANDS | STDIN | INPUT FILES | ENVIRONMENT VARIABLES | ASYNCHRONOUS EVENTS | STDOUT | STDERR | OUTPUT FILES | EXTENDED DESCRIPTION | EXIT STATUS | CONSEQUENCES OF ERRORS | APPLICATION USAGE | EXAMPLES | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT |
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PATHCHK(1P) POSIX Programmer's Manual PATHCHK(1P)
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.
pathchk — check pathnames
pathchk [-p] [-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 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.1‐2017, limits.h(0p))
* 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.
The pathchk utility shall conform to the Base Definitions volume
of POSIX.1‐2017, 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.1‐2017, limits.h(0p))
* 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-minus> character
* Is empty
The following operand shall be supported:
pathname A pathname to be checked.
Not used.
None.
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.1‐2017, 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.
Default.
Not used.
The standard error shall be used only for diagnostic messages.
None.
None.
The following exit values shall be returned:
0 All pathname operands passed all of the checks.
>0 An error occurred.
Default.
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(1p) special built-
in) can be used to atomically create a file. As with all file
creation semantics in the System Interfaces volume of
POSIX.1‐2017, 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.
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.1‐2017 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.
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-minus> character as the first character in a component of
the pathname, or for an empty pathname operand.
None.
Section 2.7, Redirection, set(1p), test(1p)
The Base Definitions volume of POSIX.1‐2017, Chapter 8,
Environment Variables, Section 12.2, Utility Syntax Guidelines,
limits.h(0p)
Portions of this text are reprinted and reproduced in electronic
form from IEEE Std 1003.1-2017, Standard for Information
Technology -- Portable Operating System Interface (POSIX), The
Open Group Base Specifications Issue 7, 2018 Edition, Copyright
(C) 2018 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 .
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 .
IEEE/The Open Group 2017 PATHCHK(1P)
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HTML rendering created 2024-06-26 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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