WORDEXP(3C)WORDEXP(3C)NAME
wordexp, wordfree - perform word expansions
SYNOPSIS
#include <wordexp.h>
int wordexp(const char *restrict words, wordexp_t *restrict pwordexp,
int flags);
void wordfree(wordexp_t *pwordexp);
DESCRIPTION
The wordexp() function performs word expansions, subject to quoting,
and places the list of expanded words into the structure pointed to by
pwordexp.
The wordfree() function frees any memory allocated by wordexp() associ‐
ated 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 per‐
formed by the shell if words were the part of a command line represent‐
ing 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 com‐
ment character (number sign) that is the beginning of a token, word‐
exp() 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 pword‐
exp−>we_wordv.
The wordexp() function stores the number of generated words into pword‐
exp−>we_wordc and a pointer to a list of pointers to words in pword‐
exp−>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
pointer.
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() func‐
tion 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 fol‐
lowing constants, which are defined in <wordexp.h>:
WRDE_APPEND
Append words generated to the ones from a previous call
to wordexp().
WRDE_DOOFFS
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 pword‐
exp−>we_offs NULL pointers, followed by pword‐
exp−>we_wordc word pointers, followed by a NULL
pointer.
WRDE_NOCMD
Fail if command substitution is requested.
WRDE_REUSE
The pwordexp argument was passed to a previous success‐
ful call to wordexp(), and has not been passed to word‐
free(). The result will be the same as if the applica‐
tion had called wordfree() and then called wordexp()
without WRDE_REUSE.
WRDE_SHOWERR
Do not redirect stderr to /dev/null.
WRDE_UNDEF
Report error on an attempt to expand an undefined shell
variable.
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, pword‐
exp−>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 pword‐
exp−>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 flag.
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 substitu‐
tion while expanding words.
If WRDE_SHOWERR is set, wordexp() may write messages to stderr if syn‐
tax 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:
WRDE_BADCHAR
One of the unquoted characters:
NEWLINE | & ; < > ( ) { }
appears in words in an inappropriate context.
WRDE_BADVAL
Reference to undefined shell variable when WRDE_UNDEF
is set in flags.
WRDE_CMDSUB
Command substitution requested when WRDE_NOCMD was set
in flags.
WRDE_NOSPACE
Attempt to allocate memory failed.
WRDE_SYNTAX
Shell syntax error, such as unbalanced parentheses or
unterminated string.
RETURN VALUES
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 modified.
The wordfree() function returns no value.
ERRORS
No errors are defined.
USAGE
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.
ATTRIBUTES
See attributes(5) for descriptions of the following attributes:
┌────────────────────┬─────────────────┐
│ ATTRIBUTE TYPE │ ATTRIBUTE VALUE │
├────────────────────┼─────────────────┤
│Interface Stability │ Standard │
├────────────────────┼─────────────────┤
│MT-Level │ MT-Safe │
└────────────────────┴─────────────────┘
SEE ALSOfnmatch(3C), glob(3C), attributes(5), standards(5)
Nov 1, 2003 WORDEXP(3C)
