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

NAME

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

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.

VERSIONS

       wordexp() and wordfree() are provided in glibc since version 2.1.

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.

CONFORMING TO

       POSIX.1-2001, POSIX.1-2008.

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(int argc, char *argv[])
       {
           wordexp_t p;
           char **w;

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

COLOPHON

       This  page  is  part of release 5.13 of the Linux man-pages project.  A description of the
       project, information about reporting bugs, and the latest version of  this  page,  can  be
       found at https://www.kernel.org/doc/man-pages/.

                                            2021-08-27                                 WORDEXP(3)