Ubuntu Manpage: wordexp, wordfree - perform word expansion like a posix-shell

NAME

       wordexp, wordfree - perform word expansion like a posix-shell

LIBRARY

       Standard C library (libc, -lc)

SYNOPSIS

       #include <wordexp.h>

       int wordexp(const char *restrict s, wordexp_t *restrict p, int flags);
       void wordfree(wordexp_t *p);

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

       wordexp(), wordfree():
           _XOPEN_SOURCE

DESCRIPTION

The function wordexp() performs a shell-like expansion of the string s and returns the
result in the structure pointed to by p. The data type wordexp_t is a structure that at
least has the fields we_wordc, we_wordv, and we_offs. The field we_wordc is a size_t that
gives the number of words in the expansion of s. The field we_wordv is a char ** that
points to the array of words found. The field we_offs of type size_t is sometimes
(depending on flags, see below) used to indicate the number of initial elements in the
we_wordv array that should be filled with NULLs.

The function wordfree() frees the allocated memory again. More precisely, it does not
free its argument, but it frees the array we_wordv and the strings that points to.

The string argument
Since the expansion is the same as the expansion by the shell (see sh(1)) of the
parameters to a command, the string s must not contain characters that would be illegal in
shell command parameters. In particular, there must not be any unescaped newline or |, &,
;, <, >, (, ), {, } characters outside a command substitution or parameter substitution
context.

If the argument s contains a word that starts with an unquoted comment character #, then
it is unspecified whether that word and all following words are ignored, or the # is
treated as a non-comment character.

The expansion
The expansion done consists of the following stages: tilde expansion (replacing ~user by
user's home directory), variable substitution (replacing $FOO by the value of the
environment variable FOO), command substitution (replacing $(command) or `command` by the
output of command), arithmetic expansion, field splitting, wildcard expansion, quote
removal.

The result of expansion of special parameters ($@, $*, $#, $?, $-, $$, $!, $0) is
unspecified.

Field splitting is done using the environment variable $IFS. If it is not set, the field
separators are space, tab, and newline.

The output array
The array we_wordv contains the words found, followed by a NULL.

The flags argument
The flag argument is a bitwise inclusive OR of the following values:

WRDE_APPEND
Append the words found to the array resulting from a previous call.

WRDE_DOOFFS
Insert we_offs initial NULLs in the array we_wordv. (These are not counted in the
returned we_wordc.)

WRDE_NOCMD
Don't do command substitution.

WRDE_REUSE
The argument p resulted from a previous call to wordexp(), and wordfree() was not
called. Reuse the allocated storage.

WRDE_SHOWERR
Normally during command substitution stderr is redirected to /dev/null. This flag
specifies that stderr is not to be redirected.

WRDE_UNDEF
Consider it an error if an undefined shell variable is expanded.

RETURN VALUE

       On  success,  wordexp()  returns  0.   On  failure, wordexp() returns one of the following
       nonzero values:

       WRDE_BADCHAR
              Illegal occurrence of newline or one of |, &, ;, <, >, (, ), {, }.

       WRDE_BADVAL
              An undefined shell variable was referenced, and the  WRDE_UNDEF  flag  told  us  to
              consider this an error.

       WRDE_CMDSUB
              Command substitution requested, but the WRDE_NOCMD flag told us to consider this an
              error.

       WRDE_NOSPACE
              Out of memory.

       WRDE_SYNTAX
              Shell syntax error, such as unbalanced parentheses or unmatched quotes.

ATTRIBUTES

       For an explanation of the terms used in this section, see attributes(7).

       ┌───────────┬───────────────┬─────────────────────────────────────────────────────────────┐
       │Interface  │ Attribute     │ Value                                                       │
       ├───────────┼───────────────┼─────────────────────────────────────────────────────────────┤
       │wordexp()  │ Thread safety │ MT-Unsafe race:utent const:env env sig:ALRM timer locale    │
       ├───────────┼───────────────┼─────────────────────────────────────────────────────────────┤
       │wordfree() │ Thread safety │ MT-Safe                                                     │
       └───────────┴───────────────┴─────────────────────────────────────────────────────────────┘
       In the  above  table,  utent  in  race:utent  signifies  that  if  any  of  the  functions
       setutent(3),  getutent(3),  or  endutent(3) are used in parallel in different threads of a
       program, then data races  could  occur.   wordexp()  calls  those  functions,  so  we  use
       race:utent to remind users.

STANDARDS

       POSIX.1-2008.

HISTORY

       POSIX.1-2001.  glibc 2.1.

EXAMPLES

       The output of the following example program is approximately that of "ls [a-c]*.c".

       #include <stdio.h>
       #include <stdlib.h>
       #include <wordexp.h>

       int
       main(void)
       {
           wordexp_t p;
           char **w;

           wordexp("[a-c]*.c", &p, 0);
           w = p.we_wordv;
           for (size_t i = 0; i < p.we_wordc; i++)
               printf("%s\n", w[i]);
           wordfree(&p);
           exit(EXIT_SUCCESS);
       }