1WORDEXP(3P) POSIX Programmer's Manual WORDEXP(3P)
2
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 wordexp, wordfree — perform word expansions
14
16 #include <wordexp.h>
17 int wordexp(const char *restrict words, wordexp_t *restrict pwordexp,
19 int flags);
20 void wordfree(wordexp_t *pwordexp);
21
23 The wordexp() function shall perform word expansions as described in
24 the Shell and Utilities volume of POSIX.1‐2008, Section 2.6, Word
25 Expansions, subject to quoting as described in the Shell and Utilities
26 volume of POSIX.1‐2008, Section 2.2, Quoting, and place the list of
27 expanded words into the structure pointed to by pwordexp.
28 The words argument is a pointer to a string containing one or more
30 words to be expanded. The expansions shall be the same as would be per‐
31 formed by the command line interpreter if words were the part of a com‐
32 mand line representing the arguments to a utility. Therefore, the
33 application shall ensure that words does not contain an unquoted <new‐
34 line> character or any of the unquoted shell special characters '|',
35 '&', ';', '<', '>' except in the context of command substitution as
36 specified in the Shell and Utilities volume of POSIX.1‐2008, Section
37 2.6.3, Command Substitution. It also shall not contain unquoted paren‐
38 theses or braces, except in the context of command or variable substi‐
39 tution. The application shall ensure that every member of words which
40 it expects to have expanded by wordexp() does not contain an unquoted
41 initial comment character. The application shall also ensure that any
42 words which it intends to be ignored (because they begin or continue a
43 comment) are deleted from words. If the argument words contains an
44 unquoted comment character (<number-sign>) that is the beginning of a
45 token, wordexp() shall either treat the comment character as a regular
46 character, or interpret it as a comment indicator and ignore the
47 remainder of words.
48 The structure type wordexp_t is defined in the <wordexp.h> header and
50 includes at least the following members:
51 ┌──────────────┬──────────────┬────────────────────────────────────┐
53 │Member Type │ Member Name │ Description │
54 ├──────────────┼──────────────┼────────────────────────────────────┤
55 │size_t │we_wordc │ Count of words matched by words. │
56 │char ** │we_wordv │ Pointer to list of expanded words. │
57 │size_t │we_offs │ Slots to reserve at the beginning │
58 │ │ │ of pwordexp->we_wordv. │
59 └──────────────┴──────────────┴────────────────────────────────────┘
60 The wordexp() function shall store the number of generated words into
61 pwordexp->we_wordc and a pointer to a list of pointers to words in
62 pwordexp->we_wordv. Each individual field created during field split‐
63 ting (see the Shell and Utilities volume of POSIX.1‐2008, Section
64 2.6.5, Field Splitting) or pathname expansion (see the Shell and Utili‐
65 ties volume of POSIX.1‐2008, Section 2.6.6, Pathname Expansion) shall
66 be a separate word in the pwordexp->we_wordv list. The words shall be
67 in order as described in the Shell and Utilities volume of
68 POSIX.1‐2008, Section 2.6, Word Expansions. The first pointer after
69 the last word pointer shall be a null pointer. The expansion of spe‐
70 cial parameters described in the Shell and Utilities volume of
71 POSIX.1‐2008, Section 2.5.2, Special Parameters is unspecified.
72 It is the caller's responsibility to allocate the storage pointed to by
74 pwordexp. The wordexp() function shall allocate other space as needed,
75 including memory pointed to by pwordexp->we_wordv. The wordfree() func‐
76 tion frees any memory associated with pwordexp from a previous call to
77 wordexp().
78 The flags argument is used to control the behavior of wordexp(). The
80 value of flags is the bitwise-inclusive OR of zero or more of the fol‐
81 lowing constants, which are defined in <wordexp.h>:
82 WRDE_APPEND Append words generated to the ones from a previous call
84 to wordexp().
85 WRDE_DOOFFS Make use of pwordexp->we_offs. If this flag is set,
87 pwordexp->we_offs is used to specify how many null point‐
88 ers to add to the beginning of pwordexp->we_wordv. In
89 other words, pwordexp->we_wordv shall point to pword‐
90 exp->we_offs null pointers, followed by pword‐
91 exp->we_wordc word pointers, followed by a null pointer.
92 WRDE_NOCMD If the implementation supports the utilities defined in
94 the Shell and Utilities volume of POSIX.1‐2008, fail if
95 command substitution, as specified in the Shell and Util‐
96 ities volume of POSIX.1‐2008, Section 2.6.3, Command Sub‐
97 stitution, is requested.
98 WRDE_REUSE The pwordexp argument was passed to a previous successful
100 call to wordexp(), and has not been passed to wordfree().
101 The result shall be the same as if the application had
102 called wordfree() and then called wordexp() without
103 WRDE_REUSE.
104 WRDE_SHOWERR Do not redirect stderr to /dev/null.
106 WRDE_UNDEF Report error on an attempt to expand an undefined shell
108 variable.
109 The WRDE_APPEND flag can be used to append a new set of words to those
111 generated by a previous call to wordexp(). The following rules apply
112 to applications when two or more calls to wordexp() are made with the
113 same value of pwordexp and without intervening calls to wordfree():
114 1. The first such call shall not set WRDE_APPEND. All subsequent calls
116 shall set it.
117 2. All of the calls shall set WRDE_DOOFFS, or all shall not set it.
119 3. After the second and each subsequent call, pwordexp->we_wordv shall
121 point to a list containing the following:
122 a. Zero or more null pointers, as specified by WRDE_DOOFFS and
124 pwordexp->we_offs
125 b. Pointers to the words that were in the pwordexp->we_wordv list
127 before the call, in the same order as before
128 c. Pointers to the new words generated by the latest call, in the
130 specified order
131 4. The count returned in pwordexp->we_wordc shall be the total number
133 of words from all of the calls.
134 5. The application can change any of the fields after a call to word‐
136 exp(), but if it does it shall reset them to the original value
137 before a subsequent call, using the same pwordexp value, to word‐
138 free() or wordexp() with the WRDE_APPEND or WRDE_REUSE flag.
139 If the implementation supports the utilities defined in the Shell and
141 Utilities volume of POSIX.1‐2008, and words contains an unquoted char‐
142 acter—<newline>, '|', '&', ';', '<', '>', '(', ')', '{', '}'—in an
143 inappropriate context, wordexp() shall fail, and the number of expanded
144 words shall be 0.
145 Unless WRDE_SHOWERR is set in flags, wordexp() shall redirect stderr to
147 /dev/null for any utilities executed as a result of command substitu‐
148 tion while expanding words. If WRDE_SHOWERR is set, wordexp() may
149 write messages to stderr if syntax errors are detected while expanding
150 words; however, it is unspecified whether any write errors encountered
151 while outputting such messages will affect the stderr error indicator
152 or the value of errno.
153 The application shall ensure that if WRDE_DOOFFS is set, then pword‐
155 exp->we_offs has the same value for each wordexp() call and wordfree()
156 call using a given pwordexp.
157 The following constants are defined as error return values:
159 WRDE_BADCHAR One of the unquoted characters—<newline>, '|', '&', ';',
161 '<', '>', '(', ')', '{', '}'—appears in words in an inap‐
162 propriate context.
163 WRDE_BADVAL Reference to undefined shell variable when WRDE_UNDEF is
165 set in flags.
166 WRDE_CMDSUB Command substitution requested when WRDE_NOCMD was set in
168 flags.
169 WRDE_NOSPACE Attempt to allocate memory failed.
171 WRDE_SYNTAX Shell syntax error, such as unbalanced parentheses or
173 unterminated string.
174
176 Upon successful completion, wordexp() shall return 0. Otherwise, a non-
177 zero value, as described in <wordexp.h>, shall be returned to indicate
178 an error. If wordexp() returns the value WRDE_NOSPACE, then pword‐
179 exp->we_wordc and pwordexp->we_wordv shall be updated to reflect any
180 words that were successfully expanded. In other cases, they shall not
181 be modified.
182 The wordfree() function shall not return a value.
184
186 No errors are defined.
187 The following sections are informative.
189
191 None.
192
194 The wordexp() function is intended to be used by an application that
195 wants to do all of the shell's expansions on a word or words obtained
196 from a user. For example, if the application prompts for a pathname (or
197 list of pathnames) and then uses wordexp() to process the input, the
198 user could respond with anything that would be valid as input to the
199 shell.
200 The WRDE_NOCMD flag is provided for applications that, for security or
202 other reasons, want to prevent a user from executing shell commands.
203 Disallowing unquoted shell special characters also prevents unwanted
204 side-effects, such as executing a command or writing a file.
205 POSIX.1‐2008 does not require the wordexp() function to be thread-safe
207 if passed an expression referencing an environment variable while any
208 other thread is concurrently modifying any environment variable; see
209 exec.
210 Even though the WRDE_SHOWERR flag allows the implementation to write
212 messages to stderr during command substitution or syntax errors, this
213 standard does not provide any way to detect write failures during the
214 output of such messages.
215
217 This function was included as an alternative to glob(). There had been
218 continuing controversy over exactly what features should be included in
219 glob(). It is hoped that by providing wordexp() (which provides all of
220 the shell word expansions, but which may be slow to execute) and glob()
221 (which is faster, but which only performs pathname expansion, without
222 tilde or parameter expansion) this will satisfy the majority of appli‐
223 cations.
224 While wordexp() could be implemented entirely as a library routine, it
226 is expected that most implementations run a shell in a subprocess to do
227 the expansion.
228 Two different approaches have been proposed for how the required infor‐
230 mation might be presented to the shell and the results returned. They
231 are presented here as examples.
232 One proposal is to extend the echo utility by adding a −q option. This
234 option would cause echo to add a <backslash> before each <backslash>
235 and <blank> that occurs within an argument. The wordexp() function
236 could then invoke the shell as follows:
237 (void) strcpy(buffer, "echo -q");
239 (void) strcat(buffer, words);
240 if ((flags & WRDE_SHOWERR) == 0)
241 (void) strcat(buffer, "2>/dev/null");
242 f = popen(buffer, "r");
243 The wordexp() function would read the resulting output, remove unquoted
245 <backslash> characters, and break into words at unquoted <blank> char‐
246 acters. If the WRDE_NOCMD flag was set, wordexp() would have to scan
247 words before starting the subshell to make sure that there would be no
248 command substitution. In any case, it would have to scan words for
249 unquoted special characters.
250 Another proposal is to add the following options to sh:
252 −w wordlist
254 This option provides a wordlist expansion service to applica‐
255 tions. The words in wordlist shall be expanded and the following
256 written to standard output:
257 1. The count of the number of words after expansion, in decimal,
259 followed by a null byte
260 2. The number of bytes needed to represent the expanded words
262 (not including null separators), in decimal, followed by a
263 null byte
264 3. The expanded words, each terminated by a null byte
266 If an error is encountered during word expansion, sh exits with a
268 non-zero status after writing the former to report any words suc‐
269 cessfully expanded
270 −P Run in ``protected'' mode. If specified with the −w option, no
272 command substitution shall be performed.
273 With these options, wordexp() could be implemented fairly simply by
275 creating a subprocess using fork() and executing sh using the line:
276 execl(<shell path>, "sh", "-P", "-w", words, (char *)0);
278 after directing standard error to /dev/null.
280 It seemed objectionable for a library routine to write messages to
282 standard error, unless explicitly requested, so wordexp() is required
283 to redirect standard error to /dev/null to ensure that no messages are
284 generated, even for commands executed for command substitution. The
285 WRDE_SHOWERR flag can be specified to request that error messages be
286 written.
287 The WRDE_REUSE flag allows the implementation to avoid the expense of
289 freeing and reallocating memory, if that is possible. A minimal imple‐
290 mentation can call wordfree() when WRDE_REUSE is set.
291
293 None.
294
296 exec, fnmatch(), glob()
297 The Base Definitions volume of POSIX.1‐2008, <wordexp.h>
299 The Shell and Utilities volume of POSIX.1‐2008, Chapter 2, Shell Com‐
301 mand Language
302
304 Portions of this text are reprinted and reproduced in electronic form
305 from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
306 -- Portable Operating System Interface (POSIX), The Open Group Base
307 Specifications Issue 7, Copyright (C) 2013 by the Institute of Electri‐
308 cal and Electronics Engineers, Inc and The Open Group. (This is
309 POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) In the
310 event of any discrepancy between this version and the original IEEE and
311 The Open Group Standard, the original IEEE and The Open Group Standard
312 is the referee document. The original Standard can be obtained online
313 at http://www.unix.org/online.html .
314 Any typographical or formatting errors that appear in this page are
316 most likely to have been introduced during the conversion of the source
317 files to man page format. To report such errors, see https://www.ker‐
318 nel.org/doc/man-pages/reporting_bugs.html .
319IEEE/The Open Group 2013 WORDEXP(3P)