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[Linux manuál]

wordexp, wordfree: provádět rozšíření slov jako posix-shell

Originální popis anglicky: wordexp, wordfree - perform word expansion like a posix-shell

Návod, kniha: Linux Programmer's Manual


#include <wordexp.h>
int wordexp(const char *s, wordexp_t *p, int flags);
void wordfree(wordexp_t *p);


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.


First a small example. The output is approximately that of "ls [a-c]*.c".
#include <stdio.h>
#include <wordexp.h>
int main(int argc, char **argv) { wordexp_t p; char **w; int i;
wordexp("[a-c]*.c", &p, 0); w = p.we_wordv; for (i=0; i<p.we_wordc; i++) printf("%s\n", w[i]); wordfree(&p); return 0; }


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 non-escaped 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:
Append the words found to the array resulting from a previous call.
Insert we_offs initial NULLs in the array we_wordv. (These are not counted in the returned we_wordc.)
Don't do command substitution.
The parameter p resulted from a previous call to wordexp(), and wordfree() was not called. Reuse the allocated storage.
Normally during command substitution stderr is redirected to /dev/null. This flag specifies that stderr is not to be redirected.
Consider it an error if an undefined shell variable is expanded.


In case of success 0 is returned. In case of error one of the following five values is returned.
Illegal occurrence of newline or one of |, &, ;, <, >, (, ), {, }.
An undefined shell variable was referenced, and the WRDE_UNDEF flag told us to consider this an error.
Command substitution occurred, and the WRDE_NOCMD flag told us to consider this an error.
Out of memory.
Shell syntax error, such as unbalanced parentheses or unmatched quotes.


XPG4, POSIX 1003.1-2003


fnmatch(3), glob(3)
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