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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12 wordexp, wordfree - perform word expansions
13
15 #include <wordexp.h>
16 int wordexp(const char *restrict words, wordexp_t *restrict pwordexp,
18 int flags);
19 void wordfree(wordexp_t *pwordexp);
20
23 The wordexp() function shall perform word expansions as described in
24 the Shell and Utilities volume of IEEE Std 1003.1-2001, Section 2.6,
25 Word Expansions, subject to quoting as in the Shell and Utilities vol‐
26 ume of IEEE Std 1003.1-2001, Section 2.2, Quoting, and place the list
27 of 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> or any of the unquoted shell special characters '|', '&', ';',
35 '<', '>' except in the context of command substitution as specified in
36 the Shell and Utilities volume of IEEE Std 1003.1-2001, Section 2.6.3,
37 Command Substitution. It also shall not contain unquoted parentheses
38 or braces, except in the context of command or variable substitution.
39 The application shall ensure that every member of words which it
40 expects to have expanded by wordexp() does not contain an unquoted ini‐
41 tial 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 Member Type Member Name Description
53 size_t we_wordc Count of words matched by words.
54 char ** we_wordv Pointer to list of expanded words.
55 size_t we_offs Slots to reserve at the beginning of
56 pwordexp->we_wordv.
57 The wordexp() function shall store the number of generated words into
59 pwordexp->we_wordc and a pointer to a list of pointers to words in
60 pwordexp->we_wordv. Each individual field created during field split‐
61 ting (see the Shell and Utilities volume of IEEE Std 1003.1-2001, Sec‐
62 tion 2.6.5, Field Splitting) or pathname expansion (see the Shell and
63 Utilities volume of IEEE Std 1003.1-2001, Section 2.6.6, Pathname
64 Expansion) shall be a separate word in the pwordexp->we_wordv list. The
65 words shall be in order as described in the Shell and Utilities volume
66 of IEEE Std 1003.1-2001, Section 2.6, Word Expansions. The first
67 pointer after the last word pointer shall be a null pointer. The expan‐
68 sion of special parameters described in the Shell and Utilities volume
69 of IEEE Std 1003.1-2001, Section 2.5.2, Special Parameters is unspeci‐
70 fied.
71 It is the caller's responsibility to allocate the storage pointed to by
73 pwordexp. The wordexp() function shall allocate other space as needed,
74 including memory pointed to by pwordexp->we_wordv. The wordfree()
75 function frees any memory associated with pwordexp from a previous call
76 to wordexp().
77 The flags argument is used to control the behavior of wordexp(). The
79 value of flags is the bitwise-inclusive OR of zero or more of the fol‐
80 lowing constants, which are defined in <wordexp.h>:
81 WRDE_APPEND
83 Append words generated to the ones from a previous call to word‐
84 exp().
85 WRDE_DOOFFS
87 Make use of pwordexp->we_offs. If this flag is set, pword‐
88 exp->we_offs is used to specify how many null pointers to add to
89 the beginning of pwordexp->we_wordv. In other words, pword‐
90 exp->we_wordv shall point to pwordexp->we_offs null pointers,
91 followed by pwordexp->we_wordc word pointers, followed by a null
92 pointer.
93 WRDE_NOCMD
95 If the implementation supports the utilities defined in the
96 Shell and Utilities volume of IEEE Std 1003.1-2001, fail if com‐
97 mand substitution, as specified in the Shell and Utilities vol‐
98 ume of IEEE Std 1003.1-2001, Section 2.6.3, Command Substitu‐
99 tion, is requested.
100 WRDE_REUSE
102 The pwordexp argument was passed to a previous successful call
103 to wordexp(), and has not been passed to wordfree(). The result
104 shall be the same as if the application had called wordfree()
105 and then called wordexp() without WRDE_REUSE.
106 WRDE_SHOWERR
108 Do not redirect stderr to /dev/null.
109 WRDE_UNDEF
111 Report error on an attempt to expand an undefined shell vari‐
112 able.
113 The WRDE_APPEND flag can be used to append a new set of words to those
116 generated by a previous call to wordexp(). The following rules apply to
117 applications when two or more calls to wordexp() are made with the same
118 value of pwordexp and without intervening calls to wordfree():
119 1. The first such call shall not set WRDE_APPEND. All subsequent calls
121 shall set it.
122 2. All of the calls shall set WRDE_DOOFFS, or all shall not set it.
124 3. After the second and each subsequent call, pwordexp->we_wordv shall
126 point to a list containing the following:
127 a. Zero or more null pointers, as specified by WRDE_DOOFFS and
129 pwordexp->we_offs
130 b. Pointers to the words that were in the pwordexp->we_wordv list
132 before the call, in the same order as before
133 c. Pointers to the new words generated by the latest call, in the
135 specified order
136 4. The count returned in pwordexp->we_wordc shall be the total number
138 of words from all of the calls.
139 5. The application can change any of the fields after a call to word‐
141 exp(), but if it does it shall reset them to the original value
142 before a subsequent call, using the same pwordexp value, to word‐
143 free() or wordexp() with the WRDE_APPEND or WRDE_REUSE flag.
144 If the implementation supports the utilities defined in the Shell and
146 Utilities volume of IEEE Std 1003.1-2001, and words contains an
147 unquoted character- <newline>, '|', '&', ';', '<', '>', '(', ')', '{',
148 '}' - in an inappropriate context, wordexp() shall fail, and the number
149 of expanded words shall be 0.
150 Unless WRDE_SHOWERR is set in flags, wordexp() shall redirect stderr to
152 /dev/null for any utilities executed as a result of command substitu‐
153 tion while expanding words. If WRDE_SHOWERR is set, wordexp() may
154 write messages to stderr if syntax errors are detected while expanding
155 words.
156 The application shall ensure that if WRDE_DOOFFS is set, then pword‐
158 exp->we_offs has the same value for each wordexp() call and wordfree()
159 call using a given pwordexp.
160 The following constants are defined as error return values:
162 WRDE_BADCHAR
164 One of the unquoted characters- <newline>, '|', '&', ';', '<',
165 '>', '(', ')', '{', '}' - appears in words in an inappropriate
166 context.
167 WRDE_BADVAL
169 Reference to undefined shell variable when WRDE_UNDEF is set in
170 flags.
171 WRDE_CMDSUB
173 Command substitution requested when WRDE_NOCMD was set in flags.
174 WRDE_NOSPACE
176 Attempt to allocate memory failed.
177 WRDE_SYNTAX
179 Shell syntax error, such as unbalanced parentheses or untermi‐
180 nated string.
181
184 Upon successful completion, wordexp() shall return 0. Otherwise, a non-
185 zero value, as described in <wordexp.h>, shall be returned to indicate
186 an error. If wordexp() returns the value WRDE_NOSPACE, then pword‐
187 exp->we_wordc and pwordexp->we_wordv shall be updated to reflect any
188 words that were successfully expanded. In other cases, they shall not
189 be modified.
190 The wordfree() function shall not return a value.
192
194 No errors are defined.
195 The following sections are informative.
197
199 None.
200
202 The wordexp() function is intended to be used by an application that
203 wants to do all of the shell's expansions on a word or words obtained
204 from a user. For example, if the application prompts for a filename (or
205 list of filenames) and then uses wordexp() to process the input, the
206 user could respond with anything that would be valid as input to the
207 shell.
208 The WRDE_NOCMD flag is provided for applications that, for security or
210 other reasons, want to prevent a user from executing shell commands.
211 Disallowing unquoted shell special characters also prevents unwanted
212 side effects, such as executing a command or writing a file.
213
215 This function was included as an alternative to glob(). There had been
216 continuing controversy over exactly what features should be included in
217 glob(). It is hoped that by providing wordexp() (which provides all of
218 the shell word expansions, but which may be slow to execute) and glob()
219 (which is faster, but which only performs pathname expansion, without
220 tilde or parameter expansion) this will satisfy the majority of appli‐
221 cations.
222 While wordexp() could be implemented entirely as a library routine, it
224 is expected that most implementations run a shell in a subprocess to do
225 the expansion.
226 Two different approaches have been proposed for how the required infor‐
228 mation might be presented to the shell and the results returned. They
229 are presented here as examples.
230 One proposal is to extend the echo utility by adding a -q option. This
232 option would cause echo to add a backslash before each backslash and
233 <blank> that occurs within an argument. The wordexp() function could
234 then invoke the shell as follows:
235 (void) strcpy(buffer, "echo -q");
238 (void) strcat(buffer, words);
239 if ((flags & WRDE_SHOWERR) == 0)
240 (void) strcat(buffer, "2>/dev/null");
241 f = popen(buffer, "r");
242 The wordexp() function would read the resulting output, remove unquoted
244 backslashes, and break into words at unquoted <blank>s. If the
245 WRDE_NOCMD flag was set, wordexp() would have to scan words before
246 starting the subshell to make sure that there would be no command sub‐
247 stitution. In any case, it would have to scan words for unquoted spe‐
248 cial characters.
249 Another proposal is to add the following options to sh:
251 -w wordlist
253 This option provides a wordlist expansion service to applica‐
255 tions. The words in wordlist shall be expanded and the follow‐
256 ing written to standard output:
257 1. The count of the number of words after expansion, in deci‐
259 mal, 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 non-
268 zero status after writing the former to report any words successfully
269 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
276 creating a subprocess using fork() and executing sh using the line:
277 execl(<shell path>, "sh", "-P", "-w", words, (char *)0);
280 after directing standard error to /dev/null.
282 It seemed objectionable for a library routine to write messages to
284 standard error, unless explicitly requested, so wordexp() is required
285 to redirect standard error to /dev/null to ensure that no messages are
286 generated, even for commands executed for command substitution. The
287 WRDE_SHOWERR flag can be specified to request that error messages be
288 written.
289 The WRDE_REUSE flag allows the implementation to avoid the expense of
291 freeing and reallocating memory, if that is possible. A minimal imple‐
292 mentation can call wordfree() when WRDE_REUSE is set.
293
295 None.
296
298 fnmatch(), glob(), the Base Definitions volume of IEEE Std 1003.1-2001,
299 <wordexp.h>, the Shell and Utilities volume of IEEE Std 1003.1-2001,
300 Chapter 2, Shell Command Language
301
303 Portions of this text are reprinted and reproduced in electronic form
304 from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
305 -- Portable Operating System Interface (POSIX), The Open Group Base
306 Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
307 Electrical and Electronics Engineers, Inc and The Open Group. In the
308 event of any discrepancy between this version and the original IEEE and
309 The Open Group Standard, the original IEEE and The Open Group Standard
310 is the referee document. The original Standard can be obtained online
311 at http://www.opengroup.org/unix/online.html .
312IEEE/The Open Group 2003 WORDEXP(3P)