1PATHCHK(P) POSIX Programmer's Manual PATHCHK(P)
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6 pathchk - check pathnames
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9 pathchk [-p] pathname...
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12 The pathchk utility shall check that one or more pathnames are valid
13 (that is, they could be used to access or create a file without causing
14 syntax errors) and portable (that is, no filename truncation results).
15 More extensive portability checks are provided by the -p option.
16 By default, the pathchk utility shall check each component of each
18 pathname operand based on the underlying file system. A diagnostic
19 shall be written for each pathname operand that:
20 * Is longer than {PATH_MAX} bytes (see Pathname Variable Values in the
22 Base Definitions volume of IEEE Std 1003.1-2001, Chapter 13, Head‐
23 ers, <limits.h>)
24 * Contains any component longer than {NAME_MAX} bytes in its contain‐
26 ing directory
27 * Contains any component in a directory that is not searchable
29 * Contains any character in any component that is not valid in its
31 containing directory
32 The format of the diagnostic message is not specified, but shall indi‐
34 cate the error detected and the corresponding pathname operand.
35 It shall not be considered an error if one or more components of a
37 pathname operand do not exist as long as a file matching the pathname
38 specified by the missing components could be created that does not vio‐
39 late any of the checks specified above.
40
42 The pathchk utility shall conform to the Base Definitions volume of
43 IEEE Std 1003.1-2001, Section 12.2, Utility Syntax Guidelines.
44 The following option shall be supported:
46 -p Instead of performing checks based on the underlying file sys‐
48 tem, write a diagnostic for each pathname operand that:
49 * Is longer than {_POSIX_PATH_MAX} bytes (see Minimum Values in
51 the Base Definitions volume of IEEE Std 1003.1-2001, Chapter
52 13, Headers, <limits.h>)
53 * Contains any component longer than {_POSIX_NAME_MAX} bytes
55 * Contains any character in any component that is not in the
57 portable filename character set
58
60 The following operand shall be supported:
61 pathname
63 A pathname to be checked.
64
67 Not used.
68
70 None.
71
73 The following environment variables shall affect the execution of
74 pathchk:
75 LANG Provide a default value for the internationalization variables
77 that are unset or null. (See the Base Definitions volume of
78 IEEE Std 1003.1-2001, Section 8.2, Internationalization Vari‐
79 ables for the precedence of internationalization variables used
80 to determine the values of locale categories.)
81 LC_ALL If set to a non-empty string value, override the values of all
83 the other internationalization variables.
84 LC_CTYPE
86 Determine the locale for the interpretation of sequences of
87 bytes of text data as characters (for example, single-byte as
88 opposed to multi-byte characters in arguments).
89 LC_MESSAGES
91 Determine the locale that should be used to affect the format
92 and contents of diagnostic messages written to standard error.
93 NLSPATH
95 Determine the location of message catalogs for the processing of
96 LC_MESSAGES .
97
100 Default.
101
103 Not used.
104
106 The standard error shall be used only for diagnostic messages.
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109 None.
110
112 None.
113
115 The following exit values shall be returned:
116 0 All pathname operands passed all of the checks.
118 >0 An error occurred.
120
123 Default.
124 The following sections are informative.
126
128 The test utility can be used to determine whether a given pathname
129 names an existing file; it does not, however, give any indication of
130 whether or not any component of the pathname was truncated in a direc‐
131 tory where the _POSIX_NO_TRUNC feature is not in effect. The pathchk
132 utility does not check for file existence; it performs checks to deter‐
133 mine whether a pathname does exist or could be created with no pathname
134 component truncation.
135 The noclobber option in the shell (see the set special built-in) can be
137 used to atomically create a file. As with all file creation semantics
138 in the System Interfaces volume of IEEE Std 1003.1-2001, it guarantees
139 atomic creation, but still depends on applications to agree on conven‐
140 tions and cooperate on the use of files after they have been created.
141
143 To verify that all pathnames in an imported data interchange archive
144 are legitimate and unambiguous on the current system:
145 pax -f archive | sed -e '/ == .*/s///' | xargs pathchk
148 if [ $? -eq 0 ]
149 then
150 pax -r -f archive
151 else
152 echo Investigate problems before importing files.
153 exit 1
154 fi
155 To verify that all files in the current directory hierarchy could be
157 moved to any system conforming to the System Interfaces volume of
158 IEEE Std 1003.1-2001 that also supports the pax utility:
159 find . -print | xargs pathchk -p
162 if [ $? -eq 0 ]
163 then
164 pax -w -f archive .
165 else
166 echo Portable archive cannot be created.
167 exit 1
168 fi
169 To verify that a user-supplied pathname names a readable file and that
171 the application can create a file extending the given path without
172 truncation and without overwriting any existing file:
173 case $- in
176 *C*) reset="";;
177 *) reset="set +C"
178 set -C;;
179 esac
180 test -r "$path" && pathchk "$path.out" &&
181 rm "$path.out" > "$path.out"
182 if [ $? -ne 0 ]; then
183 printf "%s: %s not found or %s.out fails \
184 creation checks.\n" $0 "$path" "$path"
185 $reset # Reset the noclobber option in case a trap
186 # on EXIT depends on it.
187 exit 1
188 fi
189 $reset
190 PROCESSING < "$path" > "$path.out"
191 The following assumptions are made in this example:
193 1. PROCESSING represents the code that is used by the application to
195 use $path once it is verified that $path.out works as intended.
196 2. The state of the noclobber option is unknown when this code is
198 invoked and should be set on exit to the state it was in when this
199 code was invoked. (The reset variable is used in this example to
200 restore the initial state.)
201 3. Note the usage of:
203 rm "$path.out" > "$path.out"
206 a. The pathchk command has already verified, at this point, that
208 $path.out is not truncated.
209 b. With the noclobber option set, the shell verifies that
211 $path.out does not already exist before invoking rm.
212 c. If the shell succeeded in creating $path.out, rm removes it so
214 that the application can create the file again in the PROCESS‐
215 ING step.
216 d. If the PROCESSING step wants the file to exist already when it
218 is invoked, the:
219 rm "$path.out" > "$path.out"
222 should be replaced with:
224 > "$path.out"
227 which verifies that the file did not already exist, but leaves
229 $path.out in place for use by PROCESSING.
230
232 The pathchk utility was new for the ISO POSIX-2:1993 standard. It,
233 along with the set -C( noclobber) option added to the shell, replaces
234 the mktemp, validfnam, and create utilities that appeared in early pro‐
235 posals. All of these utilities were attempts to solve several common
236 problems:
237 * Verify the validity (for several different definitions of "valid")
239 of a pathname supplied by a user, generated by an application, or
240 imported from an external source.
241 * Atomically create a file.
243 * Perform various string handling functions to generate a temporary
245 filename.
246 The create utility, included in an early proposal, provided checking
248 and atomic creation in a single invocation of the utility; these are
249 orthogonal issues and need not be grouped into a single utility. Note
250 that the noclobber option also provides a way of creating a lock for
251 process synchronization; since it provides an atomic create, there is
252 no race between a test for existence and the following creation if it
253 did not exist.
254 Having a function like tmpnam() in the ISO C standard is important in
256 many high-level languages. The shell programming language, however, has
257 built-in string manipulation facilities, making it very easy to con‐
258 struct temporary filenames. The names needed obviously depend on the
259 application, but are frequently of a form similar to:
260 $TMPDIR/application_abbreviation$$.suffix
263 In cases where there is likely to be contention for a given suffix, a
265 simple shell for or while loop can be used with the shell noclobber
266 option to create a file without risk of collisions, as long as applica‐
267 tions trying to use the same filename name space are cooperating on the
268 use of files after they have been created.
269
271 None.
272
274 Redirection , set , test
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277 Portions of this text are reprinted and reproduced in electronic form
278 from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
279 -- Portable Operating System Interface (POSIX), The Open Group Base
280 Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
281 Electrical and Electronics Engineers, Inc and The Open Group. In the
282 event of any discrepancy between this version and the original IEEE and
283 The Open Group Standard, the original IEEE and The Open Group Standard
284 is the referee document. The original Standard can be obtained online
285 at http://www.opengroup.org/unix/online.html .
286IEEE/The Open Group 2003 PATHCHK(P)