WORDEXP(3C) Standard C Library Functions WORDEXP(3C)


wordexp, wordfree - perform word expansions


#include <wordexp.h>

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

void wordfree(wordexp_t *pwordexp);


The wordexp() function performs word expansions, subject to quoting, and
places the list of expanded words into the structure pointed to by

The wordfree() function frees any memory allocated by wordexp()
associated with pwordexp.

words Argument
The words argument is a pointer to a string containing one or more words
to be expanded. The expansions will be the same as would be performed by
the shell if words were the part of a command line representing the
arguments to a utility. Therefore, words must not contain an unquoted
NEWLINE or any of the unquoted shell special characters:

| & ; < >

except in the context of command substitution. It also must not contain
unquoted parentheses or braces, except in the context of command or
variable substitution. If the argument words contains an unquoted comment
character (number sign) that is the beginning of a token, wordexp() may
treat the comment character as a regular character, or may interpret it
as a comment indicator and ignore the remainder of words.

pwordexp Argument
The structure type wordexp_t is defined in the header <wordexp.h> and
includes at least the following members:

size_t we_wordc
Count of words matched by words.

char **we_wordv
Pointer to list of expanded words.

size_t we_offs
Slots to reserve at the beginning of

The wordexp() function stores the number of generated words into
pwordexp->we_wordc and a pointer to a list of pointers to words in
pwordexp->we_wordv. Each individual field created during field splitting
is a separate word in the pwordexp->we_wordv list. The words are in
order. The first pointer after the last word pointer will be a null

It is the caller's responsibility to allocate the storage pointed to by
pwordexp. The wordexp() function allocates other space as needed,
including memory pointed to by pwordexp->we_wordv. The wordfree()
function frees any memory associated with pwordexp from a previous call
to wordexp().

flags Argument
The flags argument is used to control the behavior of wordexp(). The
value of flags is the bitwise inclusive OR of zero or more of the
following constants, which are defined in <wordexp.h>:

Append words generated to the ones from a previous call
to wordexp().

Make use of pwordexp->we_offs. If this flag is set,
pwordexp->we_offs is used to specify how many NULL
pointers to add to the beginning of pwordexp->we_wordv.
In other words, pwordexp->we_wordv will point to
pwordexp->we_offs NULL pointers, followed by
pwordexp->we_wordc word pointers, followed by a NULL

Fail if command substitution is requested.

The pwordexp argument was passed to a previous successful
call to wordexp(), and has not been passed to wordfree().
The result will be the same as if the application had
called wordfree() and then called wordexp() without

Do not redirect stderr to /dev/null.

Report error on an attempt to expand an undefined shell

The WRDE_APPEND flag can be used to append a new set of words to those
generated by a previous call to wordexp(). The following rules apply when
two or more calls to wordexp() are made with the same value of pwordexp
and without intervening calls to wordfree():

1. The first such call must not set WRDE_APPEND. All subsequent
calls must set it.

2. All of the calls must set WRDE_DOOFFS, or all must not set it.

3. After the second and each subsequent call, pwordexp->we_wordv
will point to a list containing the following:

a. zero or more NULL pointers, as specified by WRDE_DOOFFS
and pwordexp->we_offs.

b. pointers to the words that were in the pwordexp->we_wordv
list before the call, in the same order as before.

c. pointers to the new words generated by the latest call, in
the specified order.

4. The count returned in pwordexp->we_wordc will be the total
number of words from all of the calls.

5. The application can change any of the fields after a call to
wordexp(), but if it does it must reset them to the original
value before a subsequent call, using the same pwordexp value,
to wordfree() or wordexp() with the WRDE_APPEND or WRDE_REUSE

If words contains an unquoted:

NEWLINE | & ; < > ( ) { }

in an inappropriate context, wordexp() will fail, and the number of
expanded words will be zero.

Unless WRDE_SHOWERR is set in flags, wordexp() will redirect stderr to
/dev/null for any utilities executed as a result of command substitution
while expanding words.

If WRDE_SHOWERR is set, wordexp() may write messages to stderr if syntax
errors are detected while expanding words. If WRDE_DOOFFS is set, then
pwordexp-> we_offs must have the same value for each wordexp() call and
wordfree() call using a given pwordexp.

The following constants are defined as error return values:

One of the unquoted characters:

NEWLINE | & ; < > ( ) { }

appears in words in an inappropriate context.

Reference to undefined shell variable when WRDE_UNDEF is
set in flags.

Command substitution requested when WRDE_NOCMD was set in

Attempt to allocate memory failed.

Shell syntax error, such as unbalanced parentheses or
unterminated string.


On successful completion, wordexp() returns 0.

Otherwise, a non-zero value as described in <wordexp.h> is returned to
indicate an error. If wordexp() returns the value WRDE_NOSPACE, then
pwordexp->we_wordc and pwordexp->we_wordv will be updated to reflect any
words that were successfully expanded. In other cases, they will not be

The wordfree() function returns no value.


No errors are defined.


This function is intended to be used by an application that wants to do
all of the shell's expansions on a word or words obtained from a user.
For example, if the application prompts for a filename (or list of
filenames) and then uses wordexp() to process the input, the user could
respond with anything that would be valid as input to the shell.

The WRDE_NOCMD flag is provided for applications that, for security or
other reasons, want to prevent a user from executing shell command.
Disallowing unquoted shell special characters also prevents unwanted side
effects such as executing a command or writing a file.


See attributes(7) for descriptions of the following attributes:

|Interface Stability | Standard |
|MT-Level | MT-Safe |


fnmatch(3C), glob(3C), attributes(7), standards(7)

November 1, 2003 WORDEXP(3C)