wordexp, wordfree - perform word expansion like a posix-shell
Standard C library (
libc,
-lc)
#include <wordexp.h>
int wordexp(const char *restrict s, wordexp_t *restrict p, int flags);
void wordfree(wordexp_t *p);
wordexp(),
wordfree():
_XOPEN_SOURCE
The function
wordexp() performs a shell-like expansion of the string
s and returns the result in the structure pointed to by
p. The
data type
wordexp_t is a structure that at least has the fields
we_wordc,
we_wordv, and
we_offs. The field
we_wordc is a
size_t that gives the number of words in the
expansion of
s. The field
we_wordv is a
char **
that points to the array of words found. The field
we_offs of type
size_t is sometimes (depending on
flags, see below) used to
indicate the number of initial elements in the
we_wordv array that
should be filled with NULLs.
The function
wordfree() frees the allocated memory again. More precisely,
it does not free its argument, but it frees the array
we_wordv and the
strings that points to.
Since the expansion is the same as the expansion by the shell (see
sh(1))
of the parameters to a command, the string
s must not contain
characters that would be illegal in shell command parameters. In particular,
there must not be any unescaped newline or |, &, ;, <, >, (, ), {, }
characters outside a command substitution or parameter substitution context.
If the argument
s contains a word that starts with an unquoted comment
character #, then it is unspecified whether that word and all following words
are ignored, or the # is treated as a non-comment character.
The expansion done consists of the following stages: tilde expansion (replacing
~user by user's home directory), variable substitution (replacing $FOO by the
value of the environment variable FOO), command substitution (replacing
$(command) or `command` by the output of command), arithmetic expansion, field
splitting, wildcard expansion, quote removal.
The result of expansion of special parameters ($@, $*, $#, $?, $-, $$, $!, $0)
is unspecified.
Field splitting is done using the environment variable $IFS. If it is not set,
the field separators are space, tab, and newline.
The array
we_wordv contains the words found, followed by a NULL.
The
flag argument is a bitwise inclusive OR of the following values:
- WRDE_APPEND
- Append the words found to the array resulting from a
previous call.
- WRDE_DOOFFS
- Insert we_offs initial NULLs in the array
we_wordv. (These are not counted in the returned
we_wordc.)
- WRDE_NOCMD
- Don't do command substitution.
- WRDE_REUSE
- The argument p resulted from a previous call to
wordexp(), and wordfree() was not called. Reuse the
allocated storage.
- WRDE_SHOWERR
- Normally during command substitution stderr is
redirected to /dev/null. This flag specifies that stderr is
not to be redirected.
- WRDE_UNDEF
- Consider it an error if an undefined shell variable is
expanded.
On success,
wordexp() returns 0. On failure,
wordexp() returns one
of the following nonzero values:
- WRDE_BADCHAR
- Illegal occurrence of newline or one of |, &, ;, <,
>, (, ), {, }.
- WRDE_BADVAL
- An undefined shell variable was referenced, and the
WRDE_UNDEF flag told us to consider this an error.
- WRDE_CMDSUB
- Command substitution requested, but the WRDE_NOCMD
flag told us to consider this an error.
- WRDE_NOSPACE
- Out of memory.
- WRDE_SYNTAX
- Shell syntax error, such as unbalanced parentheses or
unmatched quotes.
wordexp() and
wordfree() are provided since glibc 2.1.
For an explanation of the terms used in this section, see
attributes(7).
Interface |
Attribute |
Value |
wordexp () |
Thread safety |
MT-Unsafe race:utent const:env env sig:ALRM timer locale |
wordfree () |
Thread safety |
MT-Safe |
In the above table,
utent in
race:utent signifies that if any of
the functions
setutent(3),
getutent(3), or
endutent(3)
are used in parallel in different threads of a program, then data races could
occur.
wordexp() calls those functions, so we use race:utent to remind
users.
POSIX.1-2001, POSIX.1-2008.
The output of the following example program is approximately that of "ls
[a-c]*.c".
#include <stdio.h>
#include <stdlib.h>
#include <wordexp.h>
int
main(void)
{
wordexp_t p;
char **w;
wordexp("[a-c]*.c", &p, 0);
w = p.we_wordv;
for (size_t i = 0; i < p.we_wordc; i++)
printf("%s\n", w[i]);
wordfree(&p);
exit(EXIT_SUCCESS);
}
fnmatch(3),
glob(3)