1PATHCHK(1P) POSIX Programmer's Manual PATHCHK(1P)
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6 This manual page is part of the POSIX Programmer's Manual. The Linux
7 implementation of this interface may differ (consult the corresponding
8 Linux manual page for details of Linux behavior), or the interface may
9 not be implemented on Linux.
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13 pathchk — check pathnames
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16 pathchk [−p] [−P] pathname...
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19 The pathchk utility shall check that one or more pathnames are valid
20 (that is, they could be used to access or create a file without causing
21 syntax errors) and portable (that is, no filename truncation results).
22 More extensive portability checks are provided by the −p and −P
23 options.
24 By default, the pathchk utility shall check each component of each
26 pathname operand based on the underlying file system. A diagnostic
27 shall be written for each pathname operand that:
28 * Is longer than {PATH_MAX} bytes (see Pathname Variable Values in
30 the Base Definitions volume of POSIX.1‐2008, <limits.h>)
31 * Contains any component longer than {NAME_MAX} bytes in its contain‐
33 ing directory
34 * Contains any component in a directory that is not searchable
36 * Contains any byte sequence that is not valid in its containing
38 directory
39 The format of the diagnostic message is not specified, but shall indi‐
41 cate the error detected and the corresponding pathname operand.
42 It shall not be considered an error if one or more components of a
44 pathname operand do not exist as long as a file matching the pathname
45 specified by the missing components could be created that does not vio‐
46 late any of the checks specified above.
47
49 The pathchk utility shall conform to the Base Definitions volume of
50 POSIX.1‐2008, Section 12.2, Utility Syntax Guidelines.
51 The following option shall be supported:
53 −p Instead of performing checks based on the underlying file
55 system, write a diagnostic for each pathname operand that:
56 * Is longer than {_POSIX_PATH_MAX} bytes (see Minimum Val‐
58 ues in the Base Definitions volume of POSIX.1‐2008, <lim‐
59 its.h>)
60 * Contains any component longer than {_POSIX_NAME_MAX}
62 bytes
63 * Contains any character in any component that is not in
65 the portable filename character set
66 −P Write a diagnostic for each pathname operand that:
68 * Contains a component whose first character is the
70 <hyphen> character
71 * Is empty
73
75 The following operand shall be supported:
76 pathname A pathname to be checked.
78
80 Not used.
81
83 None.
84
86 The following environment variables shall affect the execution of
87 pathchk:
88 LANG Provide a default value for the internationalization vari‐
90 ables that are unset or null. (See the Base Definitions vol‐
91 ume of POSIX.1‐2008, Section 8.2, Internationalization Vari‐
92 ables the precedence of internationalization variables used
93 to determine the values of locale categories.)
94 LC_ALL If set to a non-empty string value, override the values of
96 all the other internationalization variables.
97 LC_CTYPE Determine the locale for the interpretation of sequences of
99 bytes of text data as characters (for example, single-byte as
100 opposed to multi-byte characters in arguments).
101 LC_MESSAGES
103 Determine the locale that should be used to affect the format
104 and contents of diagnostic messages written to standard
105 error.
106 NLSPATH Determine the location of message catalogs for the processing
108 of LC_MESSAGES.
109
111 Default.
112
114 Not used.
115
117 The standard error shall be used only for diagnostic messages.
118
120 None.
121
123 None.
124
126 The following exit values shall be returned:
127 0 All pathname operands passed all of the checks.
129 >0 An error occurred.
131
133 Default.
134 The following sections are informative.
136
138 The test utility can be used to determine whether a given pathname
139 names an existing file; it does not, however, give any indication of
140 whether or not any component of the pathname was truncated in a direc‐
141 tory where the _POSIX_NO_TRUNC feature is not in effect. The pathchk
142 utility does not check for file existence; it performs checks to deter‐
143 mine whether a pathname does exist or could be created with no pathname
144 component truncation.
145 The noclobber option in the shell (see the set special built-in) can be
147 used to atomically create a file. As with all file creation semantics
148 in the System Interfaces volume of POSIX.1‐2008, it guarantees atomic
149 creation, but still depends on applications to agree on conventions and
150 cooperate on the use of files after they have been created.
151 To verify that a pathname meets the requirements of filename portabil‐
153 ity, applications should use both the −p and −P options together.
154
156 To verify that all pathnames in an imported data interchange archive
157 are legitimate and unambiguous on the current system:
158 # This example assumes that no pathnames in the archive
160 # contain <newline> characters.
161 pax −f archive | sed −e 's/[^[:alnum:]]/\\&/g' | xargs pathchk −−
162 if [ $? −eq 0 ]
163 then
164 pax −r −f archive
165 else
166 echo Investigate problems before importing files.
167 exit 1
168 fi
169 To verify that all files in the current directory hierarchy could be
171 moved to any system conforming to the System Interfaces volume of
172 POSIX.1‐2008 that also supports the pax utility:
173 find . −exec pathchk −p −P {} +
175 if [ $? −eq 0 ]
176 then
177 pax −w −f ../archive .
178 else
179 echo Portable archive cannot be created.
180 exit 1
181 fi
182 To verify that a user-supplied pathname names a readable file and that
184 the application can create a file extending the given path without
185 truncation and without overwriting any existing file:
186 case $− in
188 *C*) reset="";;
189 *) reset="set +C"
190 set −C;;
191 esac
192 test −r "$path" && pathchk "$path.out" &&
193 rm "$path.out" > "$path.out"
194 if [ $? −ne 0 ]; then
195 printf "%s: %s not found or %s.out fails \
196 creation checks.\n" $0 "$path$path"
197 $reset # Reset the noclobber option in case a trap
198 # on EXIT depends on it.
199 exit 1
200 fi
201 $reset
202 PROCESSING < "$path" > "$path.out"
203 The following assumptions are made in this example:
205 1. PROCESSING represents the code that is used by the application to
207 use $path once it is verified that $path.out works as intended.
208 2. The state of the noclobber option is unknown when this code is
210 invoked and should be set on exit to the state it was in when this
211 code was invoked. (The reset variable is used in this example to
212 restore the initial state.)
213 3. Note the usage of:
215 rm "$path.out" > "$path.out"
217 a. The pathchk command has already verified, at this point, that
219 $path.out is not truncated.
220 b. With the noclobber option set, the shell verifies that
222 $path.out does not already exist before invoking rm.
223 c. If the shell succeeded in creating $path.out, rm removes it so
225 that the application can create the file again in the PROCESS‐
226 ING step.
227 d. If the PROCESSING step wants the file to exist already when it
229 is invoked, the:
230 rm "$path.out" > "$path.out"
232 should be replaced with:
234 > "$path.out"
236 which verifies that the file did not already exist, but leaves
238 $path.out in place for use by PROCESSING.
239
241 The pathchk utility was new for the ISO POSIX‐2:1993 standard. It,
242 along with the set −C(noclobber) option added to the shell, replaces
243 the mktemp, validfnam, and create utilities that appeared in early pro‐
244 posals. All of these utilities were attempts to solve several common
245 problems:
246 * Verify the validity (for several different definitions of
248 ``valid'') of a pathname supplied by a user, generated by an appli‐
249 cation, or imported from an external source.
250 * Atomically create a file.
252 * Perform various string handling functions to generate a temporary
254 filename.
255 The create utility, included in an early proposal, provided checking
257 and atomic creation in a single invocation of the utility; these are
258 orthogonal issues and need not be grouped into a single utility. Note
259 that the noclobber option also provides a way of creating a lock for
260 process synchronization; since it provides an atomic create, there is
261 no race between a test for existence and the following creation if it
262 did not exist.
263 Having a function like tmpnam() in the ISO C standard is important in
265 many high-level languages. The shell programming language, however, has
266 built-in string manipulation facilities, making it very easy to con‐
267 struct temporary filenames. The names needed obviously depend on the
268 application, but are frequently of a form similar to:
269 $TMPDIR/application_abbreviation$$.suffix
271 In cases where there is likely to be contention for a given suffix, a
273 simple shell for or while loop can be used with the shell noclobber
274 option to create a file without risk of collisions, as long as applica‐
275 tions trying to use the same filename name space are cooperating on the
276 use of files after they have been created.
277 For historical purposes, −p does not check for the use of the <hyphen>
279 character as the first character in a component of the pathname, or for
280 an empty pathname operand.
281
283 None.
284
286 Section 2.7, Redirection, set, test
287 The Base Definitions volume of POSIX.1‐2008, Chapter 8, Environment
289 Variables, Section 12.2, Utility Syntax Guidelines, <limits.h>
290
292 Portions of this text are reprinted and reproduced in electronic form
293 from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
294 -- Portable Operating System Interface (POSIX), The Open Group Base
295 Specifications Issue 7, Copyright (C) 2013 by the Institute of Electri‐
296 cal and Electronics Engineers, Inc and The Open Group. (This is
297 POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) In the
298 event of any discrepancy between this version and the original IEEE and
299 The Open Group Standard, the original IEEE and The Open Group Standard
300 is the referee document. The original Standard can be obtained online
301 at http://www.unix.org/online.html .
302 Any typographical or formatting errors that appear in this page are
304 most likely to have been introduced during the conversion of the source
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307IEEE/The Open Group 2013 PATHCHK(1P)