WORDEXP(3) Linux Programmer's Manual WORDEXP(3)
NAME
wordexp, wordfree - perform word expansion like a posix-shell
SYNOPSIS
#include <wordexp.h>
int wordexp(const char *restrict s, wordexp_t *restrict p, int flags);
void wordfree(wordexp_t *p);
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
wordexp(), wordfree():
_XOPEN_SOURCE
DESCRIPTION
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.
The string argument
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 substitu‐
tion 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
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 output array
The array we_wordv contains the words found, followed by a NULL.
The flags argument
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.
RETURN VALUE
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.
VERSIONS
wordexp() and wordfree() are provided in glibc since version 2.1.
ATTRIBUTES
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.
CONFORMING TO
POSIX.1-2001, POSIX.1-2008.
EXAMPLES
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(int argc, char *argv[])
{
wordexp_t p;
char **w;
wordexp("[a-c]*.c", &p, 0);
w = p.we_wordv;
for (int i = 0; i < p.we_wordc; i++)
printf("%s\n", w[i]);
wordfree(&p);
exit(EXIT_SUCCESS);
}
SEE ALSO
fnmatch(3), glob(3)
2021-08-27 WORDEXP(3)