1WORDEXP(P) POSIX Programmer's Manual WORDEXP(P)
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6 wordexp, wordfree - perform word expansions
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9 #include <wordexp.h>
10 int wordexp(const char *restrict words, wordexp_t *restrict pwordexp,
12 int flags);
13 void wordfree(wordexp_t *pwordexp);
14
17 The wordexp() function shall perform word expansions as described in
18 the Shell and Utilities volume of IEEE Std 1003.1-2001, Section 2.6,
19 Word Expansions, subject to quoting as in the Shell and Utilities vol‐
20 ume of IEEE Std 1003.1-2001, Section 2.2, Quoting, and place the list
21 of expanded words into the structure pointed to by pwordexp.
22 The words argument is a pointer to a string containing one or more
24 words to be expanded. The expansions shall be the same as would be per‐
25 formed by the command line interpreter if words were the part of a com‐
26 mand line representing the arguments to a utility. Therefore, the
27 application shall ensure that words does not contain an unquoted <new‐
28 line> or any of the unquoted shell special characters '|' , '&' , ';' ,
29 '<' , '>' except in the context of command substitution as specified in
30 the Shell and Utilities volume of IEEE Std 1003.1-2001, Section 2.6.3,
31 Command Substitution. It also shall not contain unquoted parentheses
32 or braces, except in the context of command or variable substitution.
33 The application shall ensure that every member of words which it
34 expects to have expanded by wordexp() does not contain an unquoted ini‐
35 tial comment character. The application shall also ensure that any
36 words which it intends to be ignored (because they begin or continue a
37 comment) are deleted from words. If the argument words contains an
38 unquoted comment character (number sign) that is the beginning of a
39 token, wordexp() shall either treat the comment character as a regular
40 character, or interpret it as a comment indicator and ignore the
41 remainder of words.
42 The structure type wordexp_t is defined in the <wordexp.h> header and
44 includes at least the following members:
45 Member Type Member Name Description
47 size_t we_wordc Count of words matched by words.
48 char ** we_wordv Pointer to list of expanded words.
49 size_t we_offs Slots to reserve at the beginning of
50 pwordexp->we_wordv.
51 The wordexp() function shall store the number of generated words into
53 pwordexp->we_wordc and a pointer to a list of pointers to words in
54 pwordexp->we_wordv. Each individual field created during field split‐
55 ting (see the Shell and Utilities volume of IEEE Std 1003.1-2001, Sec‐
56 tion 2.6.5, Field Splitting) or pathname expansion (see the Shell and
57 Utilities volume of IEEE Std 1003.1-2001, Section 2.6.6, Pathname
58 Expansion) shall be a separate word in the pwordexp->we_wordv list. The
59 words shall be in order as described in the Shell and Utilities volume
60 of IEEE Std 1003.1-2001, Section 2.6, Word Expansions. The first
61 pointer after the last word pointer shall be a null pointer. The expan‐
62 sion of special parameters described in the Shell and Utilities volume
63 of IEEE Std 1003.1-2001, Section 2.5.2, Special Parameters is unspeci‐
64 fied.
65 It is the caller's responsibility to allocate the storage pointed to by
67 pwordexp. The wordexp() function shall allocate other space as needed,
68 including memory pointed to by pwordexp->we_wordv. The wordfree()
69 function frees any memory associated with pwordexp from a previous call
70 to wordexp().
71 The flags argument is used to control the behavior of wordexp(). The
73 value of flags is the bitwise-inclusive OR of zero or more of the fol‐
74 lowing constants, which are defined in <wordexp.h>:
75 WRDE_APPEND
77 Append words generated to the ones from a previous call to word‐
78 exp().
79 WRDE_DOOFFS
81 Make use of pwordexp->we_offs. If this flag is set, pword‐
82 exp->we_offs is used to specify how many null pointers to add to
83 the beginning of pwordexp->we_wordv. In other words, pword‐
84 exp->we_wordv shall point to pwordexp->we_offs null pointers,
85 followed by pwordexp->we_wordc word pointers, followed by a null
86 pointer.
87 WRDE_NOCMD
89 If the implementation supports the utilities defined in the
90 Shell and Utilities volume of IEEE Std 1003.1-2001, fail if com‐
91 mand substitution, as specified in the Shell and Utilities vol‐
92 ume of IEEE Std 1003.1-2001, Section 2.6.3, Command Substitu‐
93 tion, is requested.
94 WRDE_REUSE
96 The pwordexp argument was passed to a previous successful call
97 to wordexp(), and has not been passed to wordfree(). The result
98 shall be the same as if the application had called wordfree()
99 and then called wordexp() without WRDE_REUSE.
100 WRDE_SHOWERR
102 Do not redirect stderr to /dev/null.
103 WRDE_UNDEF
105 Report error on an attempt to expand an undefined shell vari‐
106 able.
107 The WRDE_APPEND flag can be used to append a new set of words to those
110 generated by a previous call to wordexp(). The following rules apply to
111 applications when two or more calls to wordexp() are made with the same
112 value of pwordexp and without intervening calls to wordfree():
113 1. The first such call shall not set WRDE_APPEND. All subsequent calls
115 shall set it.
116 2. All of the calls shall set WRDE_DOOFFS, or all shall not set it.
118 3. After the second and each subsequent call, pwordexp->we_wordv shall
120 point to a list containing the following:
121 a. Zero or more null pointers, as specified by WRDE_DOOFFS and
123 pwordexp->we_offs
124 b. Pointers to the words that were in the pwordexp->we_wordv list
126 before the call, in the same order as before
127 c. Pointers to the new words generated by the latest call, in the
129 specified order
130 4. The count returned in pwordexp->we_wordc shall be the total number
132 of words from all of the calls.
133 5. The application can change any of the fields after a call to word‐
135 exp(), but if it does it shall reset them to the original value
136 before a subsequent call, using the same pwordexp value, to word‐
137 free() or wordexp() with the WRDE_APPEND or WRDE_REUSE flag.
138 If the implementation supports the utilities defined in the Shell and
140 Utilities volume of IEEE Std 1003.1-2001, and words contains an
141 unquoted character- <newline>, '|' , '&' , ';' , '<' , '>' , '(' , ')'
142 , '{' , '}' - in an inappropriate context, wordexp() shall fail, and
143 the number of expanded words shall be 0.
144 Unless WRDE_SHOWERR is set in flags, wordexp() shall redirect stderr to
146 /dev/null for any utilities executed as a result of command substitu‐
147 tion while expanding words. If WRDE_SHOWERR is set, wordexp() may
148 write messages to stderr if syntax errors are detected while expanding
149 words.
150 The application shall ensure that if WRDE_DOOFFS is set, then pword‐
152 exp->we_offs has the same value for each wordexp() call and wordfree()
153 call using a given pwordexp.
154 The following constants are defined as error return values:
156 WRDE_BADCHAR
158 One of the unquoted characters- <newline>, '|' , '&' , ';' , '<'
159 , '>' , '(' , ')' , '{' , '}' - appears in words in an inappro‐
160 priate context.
161 WRDE_BADVAL
163 Reference to undefined shell variable when WRDE_UNDEF is set in
164 flags.
165 WRDE_CMDSUB
167 Command substitution requested when WRDE_NOCMD was set in flags.
168 WRDE_NOSPACE
170 Attempt to allocate memory failed.
171 WRDE_SYNTAX
173 Shell syntax error, such as unbalanced parentheses or untermi‐
174 nated string.
175
178 Upon successful completion, wordexp() shall return 0. Otherwise, a non-
179 zero value, as described in <wordexp.h>, shall be returned to indicate
180 an error. If wordexp() returns the value WRDE_NOSPACE, then pword‐
181 exp->we_wordc and pwordexp->we_wordv shall be updated to reflect any
182 words that were successfully expanded. In other cases, they shall not
183 be modified.
184 The wordfree() function shall not return a value.
186
188 No errors are defined.
189 The following sections are informative.
191
193 None.
194
196 The wordexp() function is intended to be used by an application that
197 wants to do all of the shell's expansions on a word or words obtained
198 from a user. For example, if the application prompts for a filename (or
199 list of filenames) and then uses wordexp() to process the input, the
200 user could respond with anything that would be valid as input to the
201 shell.
202 The WRDE_NOCMD flag is provided for applications that, for security or
204 other reasons, want to prevent a user from executing shell commands.
205 Disallowing unquoted shell special characters also prevents unwanted
206 side effects, such as executing a command or writing a file.
207
209 This function was included as an alternative to glob(). There had been
210 continuing controversy over exactly what features should be included in
211 glob(). It is hoped that by providing wordexp() (which provides all of
212 the shell word expansions, but which may be slow to execute) and glob()
213 (which is faster, but which only performs pathname expansion, without
214 tilde or parameter expansion) this will satisfy the majority of appli‐
215 cations.
216 While wordexp() could be implemented entirely as a library routine, it
218 is expected that most implementations run a shell in a subprocess to do
219 the expansion.
220 Two different approaches have been proposed for how the required infor‐
222 mation might be presented to the shell and the results returned. They
223 are presented here as examples.
224 One proposal is to extend the echo utility by adding a -q option. This
226 option would cause echo to add a backslash before each backslash and
227 <blank> that occurs within an argument. The wordexp() function could
228 then invoke the shell as follows:
229 (void) strcpy(buffer, "echo -q");
232 (void) strcat(buffer, words);
233 if ((flags & WRDE_SHOWERR) == 0)
234 (void) strcat(buffer, "2>/dev/null");
235 f = popen(buffer, "r");
236 The wordexp() function would read the resulting output, remove unquoted
238 backslashes, and break into words at unquoted <blank>s. If the
239 WRDE_NOCMD flag was set, wordexp() would have to scan words before
240 starting the subshell to make sure that there would be no command sub‐
241 stitution. In any case, it would have to scan words for unquoted spe‐
242 cial characters.
243 Another proposal is to add the following options to sh:
245 -w wordlist
247 This option provides a wordlist expansion service to applica‐
249 tions. The words in wordlist shall be expanded and the follow‐
250 ing written to standard output:
251 1. The count of the number of words after expansion, in deci‐
253 mal, followed by a null byte
254 2. The number of bytes needed to represent the expanded words
256 (not including null separators), in decimal, followed by a
257 null byte
258 3. The expanded words, each terminated by a null byte
260 If an error is encountered during word expansion, sh exits with a non-
262 zero status after writing the former to report any words successfully
263 expanded
264 -P Run in "protected" mode. If specified with the -w option, no
266 command substitution shall be performed.
267 With these options, wordexp() could be implemented fairly simply by
270 creating a subprocess using fork() and executing sh using the line:
271 execl(<shell path>, "sh", "-P", "-w", words, (char *)0);
274 after directing standard error to /dev/null.
276 It seemed objectionable for a library routine to write messages to
278 standard error, unless explicitly requested, so wordexp() is required
279 to redirect standard error to /dev/null to ensure that no messages are
280 generated, even for commands executed for command substitution. The
281 WRDE_SHOWERR flag can be specified to request that error messages be
282 written.
283 The WRDE_REUSE flag allows the implementation to avoid the expense of
285 freeing and reallocating memory, if that is possible. A minimal imple‐
286 mentation can call wordfree() when WRDE_REUSE is set.
287
289 None.
290
292 fnmatch() , glob() , the Base Definitions volume of
293 IEEE Std 1003.1-2001, <wordexp.h>, the Shell and Utilities volume of
294 IEEE Std 1003.1-2001, Chapter 2, Shell Command Language
295
297 Portions of this text are reprinted and reproduced in electronic form
298 from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
299 -- Portable Operating System Interface (POSIX), The Open Group Base
300 Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
301 Electrical and Electronics Engineers, Inc and The Open Group. In the
302 event of any discrepancy between this version and the original IEEE and
303 The Open Group Standard, the original IEEE and The Open Group Standard
304 is the referee document. The original Standard can be obtained online
305 at http://www.opengroup.org/unix/online.html .
306IEEE/The Open Group 2003 WORDEXP(P)