The wordexp() function shall perform word expansions as described
in the Shell and Utilities volume of POSIX.1‐2017, Section 2.6,
Word Expansions, subject to quoting as described in the Shell and
Utilities volume of POSIX.1‐2017, Section 2.2, Quoting, and place
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 shall be the same as
would be performed by the command line interpreter if words were
the part of a command line representing the arguments to a
utility. Therefore, the application shall ensure that words does
not contain an unquoted <newline> character or any of the
unquoted shell special characters '|', '&', ';', '<', '>' except
in the context of command substitution as specified in the Shell
and Utilities volume of POSIX.1‐2017, Section 2.6.3, Command
Substitution. It also shall not contain unquoted parentheses or
braces, except in the context of command or variable
substitution. The application shall ensure that every member of
words which it expects to have expanded by wordexp() does not
contain an unquoted initial comment character. The application
shall also ensure that any words which it intends to be ignored
(because they begin or continue a comment) are deleted from
words. If the argument words contains an unquoted comment
character (<number-sign>) that is the beginning of a token,
wordexp() shall either treat the comment character as a regular
character, or interpret it as a comment indicator and ignore the
remainder of words.
The structure type wordexp_t is defined in the <wordexp.h> header
and includes at least the following members:
┌──────────────┬──────────────┬────────────────────────────────────┐
│Member Type │ Member Name │ 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 the beginning │
│ │ │ of pwordexp->we_wordv. │
└──────────────┴──────────────┴────────────────────────────────────┘
The wordexp() function shall store 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 (see the Shell and Utilities volume of
POSIX.1‐2017, Section 2.6.5, Field Splitting) or pathname
expansion (see the Shell and Utilities volume of POSIX.1‐2017,
Section 2.6.6, Pathname Expansion) shall be a separate word in
the pwordexp->we_wordv list. The words shall be in order as
described in the Shell and Utilities volume of POSIX.1‐2017,
Section 2.6, Word Expansions. The first pointer after the last
word pointer shall be a null pointer. The expansion of special
parameters described in the Shell and Utilities volume of
POSIX.1‐2017, Section 2.5.2, Special Parameters is unspecified.
It is the caller's responsibility to allocate the storage pointed
to by pwordexp. The wordexp() function shall allocate 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 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 shall point to pwordexp->we_offs
null pointers, followed by pwordexp->we_wordc word
pointers, followed by a null pointer.
WRDE_NOCMD If the implementation supports the utilities
defined in the Shell and Utilities volume of
POSIX.1‐2017, fail if command substitution, as
specified in the Shell and Utilities volume of
POSIX.1‐2017, Section 2.6.3, 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 shall 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 to applications 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 shall not set WRDE_APPEND. All subsequent
calls shall set it.
2. All of the calls shall set WRDE_DOOFFS, or all shall not set
it.
3. After the second and each subsequent call, pwordexp->we_wordv
shall 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 shall 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 shall 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 the implementation supports the utilities defined in the Shell
and Utilities volume of POSIX.1‐2017, and words contains an
unquoted character—<newline>, '|', '&', ';', '<', '>', '(', ')',
'{', '}'—in an inappropriate context, wordexp() shall fail, and
the number of expanded words shall be 0.
Unless WRDE_SHOWERR is set in flags, wordexp() shall 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, unless the stderr stream has wide
orientation in which case the behavior is undefined. It is
unspecified whether any write errors encountered while outputting
such messages will affect the stderr error indicator or the value
of errno.
The application shall ensure that if WRDE_DOOFFS is set, then
pwordexp->we_offs has the same value for each wordexp() call and
wordfree() call using a given pwordexp.
The results are unspecified if WRDE_APPEND and WRDE_REUSE are
both specified.
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.
