Originální popis anglicky:
pathchk - check pathnames
Návod, kniha: POSIX Programmer's Manual
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 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, 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 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
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
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 .
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 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 ]
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 $path.out,
rm removes it so that the application can create the file again in
the PROCESSING step.
- d.
- If the PROCESSING step wants the file to exist
already when it is invoked, the:
rm "$path.out" > "$path.out"
should be replaced with:
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.
None.
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 original
Standard can be obtained online at http://www.opengroup.org/unix/online.html
.
