wordexp, wordfree - perform word expansion like a posix-shell

#include <wordexp.h>

int wordexp(const char *s, wordexp_t *p, int flags);

void wordfree(wordexp_t *p);

Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

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 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

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.

In case of success 0 is returned. In case of error one of the following five values is returned.

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.

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);
}

fnmatch(3), glob(3)