Manual Pages  — WORDEXP

wordexp – perform shell-style word expansions

LIBRARY SYNOPSIS DESCRIPTION IMPLEMENTATION NOTES RETURN VALUES ENVIRONMENT EXAMPLES DIAGNOSTICS SEE ALSO STANDARDS BUGS SECURITY CONSIDERATIONS

Standard C Library (libc, -lc)

#include <wordexp.h>

int
wordexp(const char * restrict words, wordexp_t * restrict we, int flags);

void
wordfree(wordexp_t *we);

The wordexp() function performs shell-style word expansion on words and places the list of words into the we_wordv member of we, and the number of words into we_wordc.

The flags argument is the bitwise inclusive OR of any of the following constants:

WRDE_APPEND	Append the words to those generated by a previous call to wordexp().
WRDE_DOOFFS	As many NULL pointers as are specified by the we_offs member of we are added to the front of we_wordv.
WRDE_NOCMD	Disallow command substitution in words. See the note in BUGS before using this.
WRDE_REUSE	The we argument was passed to a previous successful call to wordexp() but has not been passed to wordfree(). The implementation may reuse the space allocated to it.
WRDE_SHOWERR
	Do not redirect shell error messages to /dev/null.
WRDE_UNDEF	Report error on an attempt to expand an undefined shell variable.

The wordexp_t structure is defined in <wordexp.h> as:

typedef struct {
        size_t  we_wordc;       /* count of words matched */
        char    **we_wordv;     /* pointer to list of words */
        size_t  we_offs;        /* slots to reserve in we_wordv */
} wordexp_t;

The wordfree() function frees the memory allocated by wordexp().

The wordexp() function is implemented using the undocumented freebsd_wordexp shell built-in command.

The wordexp() function returns zero if successful, otherwise it returns one of the following error codes:

WRDE_BADCHAR
	The words argument contains one of the following unquoted characters: <newline>, ‘|’, ‘&’, ‘amp;;’, ‘<’, ‘>’, ‘amp;(’, ‘amp;)’, ‘{’, ‘}’.
WRDE_BADVAL	An error after successful parsing, such as an attempt to expand an undefined shell variable with WRDE_UNDEF set in flags.
WRDE_CMDSUB	An attempt was made to use command substitution and WRDE_NOCMD is set in flags.
WRDE_NOSPACE
	Not enough memory to store the result or an error during fork(2).
WRDE_SYNTAX	Shell syntax error in words.

The wordfree() function returns no value.

IFS	Field separator.

Invoke the editor on all .c files in the current directory and /etc/motd (error checking omitted):

wordexp_t we;

wordexp("${EDITOR:-vi} *.c /etc/motd", &we, 0);
execvp(we.we_wordv[0], we.we_wordv);

Diagnostic messages from the shell are written to the standard error output if WRDE_SHOWERR is set in flags.

The wordexp() and wordfree() functions conform to IEEE Std 1003.1-2001 ("POSIX.1").

The current wordexp() implementation does not recognize multibyte characters other than UTF-8, since the shell (which it invokes to perform expansions) does not.

Pathname generation may create output that is exponentially larger than the input size.

Although this implementation detects command substitution reliably for WRDE_NOCMD, the attack surface remains fairly large. Also, some other implementations (such as older versions of this one) may execute command substitutions even if WRDE_NOCMD is set.