Tribblix: manual page: wordexp.3c

WORDEXP(3C) Standard C Library Functions 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()
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
pwordexp->we_wordv.

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 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()
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>:

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 pwordexp->we_offs
NULL pointers, followed by pwordexp->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
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 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,
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 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
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:

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