man3/wordexp.3

.\" Copyright (c) 2003 Andries Brouwer (aeb@cwi.nl)
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.TH WORDEXP 3 2021-03-22  "" "Linux Programmer's Manual"
.SH NAME
wordexp, wordfree \- perform word expansion like a posix-shell
.SH SYNOPSIS
.nf
.B "#include <wordexp.h>"
.PP
.BI "int wordexp(const char *restrict " s ", wordexp_t *restrict " p \
", int " flags );
.BI "void wordfree(wordexp_t *" p );
.fi
.PP
.RS -4
Feature Test Macro Requirements for glibc (see
.BR feature_test_macros (7)):
.RE
.PP
.BR wordexp (),
.BR wordfree ():
.nf
    _XOPEN_SOURCE
.fi
.SH DESCRIPTION
The function
.BR wordexp ()
performs a shell-like expansion of the string
.I s
and returns the result in the structure pointed to by
.IR p .
The data type
.I wordexp_t
is a structure that at least has the fields
.IR we_wordc ,
.IR we_wordv ,
and
.IR we_offs .
The field
.I we_wordc
is a
.I size_t
that gives the number of words in the expansion of
.IR s .
The field
.I we_wordv
is a
.I "char\ **"
that points to the array of words found.
The field
.I we_offs
of type
.I size_t
is sometimes (depending on
.IR flags ,
see below) used to indicate the number of initial elements in the
.I we_wordv
array that should be filled with NULLs.
.PP
The function
.BR wordfree ()
frees the allocated memory again.
More precisely, it does not free
its argument, but it frees the array
.I we_wordv
and the strings that points to.
.SS The string argument
Since the expansion is the same as the expansion by the shell (see
.BR sh (1))
of the parameters to a command, the string
.I 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.
.PP
If the argument
.I 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.
.SS The expansion
The expansion done consists of the following stages:
tilde expansion (replacing \(tiuser by user's home directory),
variable substitution (replacing $FOO by the value of the environment
variable FOO), command substitution (replacing $(command) or \`command\`
by the output of command), arithmetic expansion, field splitting,
wildcard expansion, quote removal.
.PP
The result of expansion of special parameters
($@, $*, $#, $?, $\-, $$, $!, $0) is unspecified.
.PP
Field splitting is done using the environment variable $IFS.
If it is not set, the field separators are space, tab, and newline.
.SS The output array
The array
.I we_wordv
contains the words found, followed by a NULL.
.SS The flags argument
The
.I flag
argument is a bitwise inclusive OR of the following values:
.TP
.B WRDE_APPEND
Append the words found to the array resulting from a previous call.
.TP
.B WRDE_DOOFFS
Insert
.I we_offs
initial NULLs in the array
.IR we_wordv .
(These are not counted in the returned
.IR we_wordc .)
.TP
.B WRDE_NOCMD
Don't do command substitution.
.TP
.B WRDE_REUSE
The argument
.I p
resulted from a previous call to
.BR wordexp (),
and
.BR wordfree ()
was not called.
Reuse the allocated storage.
.TP
.B WRDE_SHOWERR
Normally during command substitution
.I stderr
is redirected to
.IR /dev/null .
This flag specifies that
.I stderr
is not to be redirected.
.TP
.B WRDE_UNDEF
Consider it an error if an undefined shell variable is expanded.
.SH RETURN VALUE
On success,
.BR wordexp ()
returns 0.
On failure,
.BR wordexp ()
returns one of the following nonzero values:
.TP
.B WRDE_BADCHAR
Illegal occurrence of newline or one of |, &, ;, <, >, (, ), {, }.
.TP
.B WRDE_BADVAL
An undefined shell variable was referenced, and the
.B WRDE_UNDEF
flag
told us to consider this an error.
.TP
.B WRDE_CMDSUB
Command substitution requested, but the
.B WRDE_NOCMD
flag told us to consider this an error.
.TP
.B WRDE_NOSPACE
Out of memory.
.TP
.B WRDE_SYNTAX
Shell syntax error, such as unbalanced parentheses or
unmatched quotes.
.SH VERSIONS
.BR wordexp ()
and
.BR wordfree ()
are provided in glibc since version 2.1.
.SH ATTRIBUTES
For an explanation of the terms used in this section, see
.BR attributes (7).
.ad l
.nh
.TS
allbox;
lb lb lbx
l l l.
Interface	Attribute	Value
T{
.BR wordexp ()
T}	Thread safety	T{
MT-Unsafe race:utent const:env
env sig:ALRM timer locale
T}
T{
.BR wordfree ()
T}	Thread safety	MT-Safe
.TE
.hy
.ad
.sp 1
In the above table,
.I utent
in
.I race:utent
signifies that if any of the functions
.BR setutent (3),
.BR getutent (3),
or
.BR endutent (3)
are used in parallel in different threads of a program,
then data races could occur.
.BR wordexp ()
calls those functions,
so we use race:utent to remind users.
.SH CONFORMING TO
POSIX.1-2001, POSIX.1-2008.
.SH EXAMPLES
The output of the following example program
is approximately that of "ls [a-c]*.c".
.PP
.EX
#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\en", w[i]);
    wordfree(&p);
    exit(EXIT_SUCCESS);
}
.EE
.SH SEE ALSO
.BR fnmatch (3),
.BR glob (3)