wordexp(3G) wordexp(3G)
wordexp, wordfree - perform word expansions
#include <wordexp.h>
int wordexp(const char *words, wordexp_t *pwordexp, int flags);
void wordfree(wordexp_t *pwordexp);
wordexp performs word expansions and places the list of expanded words
into the structure pointed to by pwordexp.
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.
The structure type wordexp_t is defined in the header <wordexp.h> and
includes at least the following members:
MemberType MemberName Description
_______________________________________________________________
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 start 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
or pathname expansion 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. The expansion of special parameters is
unspecified.
It is the caller's responsibility to allocate 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.
The flags argument is used to control the behaviour of wordexp. The
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wordexp(3G) wordexp(3G)
value of flags is the bitwise inclusive OR of zero or more of the
following constants, which are defined in the header <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 wordexp->we_wordv. In other words,
wordexp->we_wordv. will point to pwordexp->we_offs null pointers,
followed by wordexp->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:
The first such call must not set WRDE_APPEND. All subsequent calls
must set it.
All of the calls must set WRDE_DOOFFS, or all must not set it.
After the second call and each subsequent call, pwordexp->we_wordv will
point to a list containing the following:
Zero or more null pointers, as specified by WRDE_DOOFFS and
pwordexp->we_offs.
Pointers to the words that were in the pwordexp->we_wordv list
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wordexp(3G) wordexp(3G)
before the call, in the same order as before.
Pointers to the new words generated by the latest call, in the
specified order.
The count returned in pwordexp->we_wordc will be the total number of
pathnames from all of the calls.
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
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wordexp(3G) wordexp(3G)
Shell syntax error, such as unbalanced parentheses or unterminated
string.
On successful completion, wordexp returns zero.
Otherwise, a non-zero value 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 were not modified.
The wordfree function returns no value.
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 commands.
Disallowing unquoted shell special characters also prevents unwanted side
effects such as executing a command or writing a file.
fnmatch(3g), glob(3g), systune(1M), <wordexp.h>.
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