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wordexp(3)
NAME
wordexp, wordfree - Perform word expansions
SYNOPSIS
#include <wordexp.h>
int wordexp(
const char *words,
wordexp_t *pwordexp,
int flags );
void wordfree(
wordexp_t *pwordexp );
LIBRARY
Standard C Library (libc)
STANDARDS
Interfaces documented on this reference page conform to industry standards
as follows:
wordexp(), wordfree(): XPG4, XPG4-UNIX
Refer to the standards(5) reference page for more information about
industry standards and associated tags.
PARAMETERS
words
Specifies the string containing the tokens to be expanded.
pwordexp
Contains a pointer to a wordexp_t structure.
flags
Contains a bit option specifying the configurable aspects of the
wordexp() function.
DESCRIPTION
The wordexp() function performs word expansions equivalent to the word
expansion that would be performed by the shell if the contents of the words
parameter were arguments on the command line. The list of expanded words
are placed in thepwordexp parameter.
The expansions are the same as that which would be performed by the shell
if the words parameter were the part of a command line representing the
parameters to a command. Therefore, the words arameter cannot contain an
unquoted newline character or any of the unquoted shell special characters:
| & ; < >
except in the case of command substitution. The words parameter also
cannot contain unquoted parentheses or braces, except in the case of
command or variable substitution. If the words parameter contains an
unquoted comment character (#) that is the beginning of a token, the
wordexp() function may treat the comment character as a regular character,
or may interpret it as a comment indicator and ignore the remainder of the
expression in the words parameter.
The wordexp() function stores the number of generated words and a pointer
to a list of pointers to words in the pwordexp parameter. Each individual
field created during the field splitting or pathname expansion is a
separate word in the list specified by the pwordexp arameter. The first
pointer after the last token in the list is a null pointer. The expansion
of special parameters *, @, #, ?, -, $, !, and 0 is unspecified. The words
are expanded in the following order:
1. Tilde expansion is performed first.
2. Parameter expansion, command substitution, and arithmetic expansion
are performed next, from beginning to end.
3. Field splitting is then performed on fields generated by step 2,
unless the IFS (Input Field Separators) is full.
4. Pathname expansion is performed, unless the set -f command is in
effect.
5. Quote removal is always performed last.
The pwordexp structure is allocated by the caller, but memory to contain
the expanded tokens is allocated by the wordexp() function and added to the
structure as needed. The wordfree() function frees any memory associated
with pwordexp() from a previous call to wordexp().
The value of the flags parameter is the bitwise inclusive OR of the
following constants, which are defined in the wordexp.h file:
WRDE_APPEND
Appends words generated to those generated by a previous call to the
wordexp() function.
WRDE_DOOFFS
Makes use of the we_offs structure. If the WRDE_DOOFFS option is set,
the we_offs structure is used to specify the number of null pointers
to add to the beginning of the we_words structure. If the WRDE_DOOFFS
option is not set in the first call to the wordexp() function with the
pwordexp parameter, it should not be set in subsequent calls to the
wordexp() function with the pwordexp parameter.
WRDE_NOCMD
Fails if command substitution is requested.
WRDE_REUSE
The pwordexp parameter was passed to a previous successful call to the
wordexp() function. Therefore, the memory previously allocated may be
reused.
WRDE_SHOWERR
Does not redirect standard error to /dev/null.
WRDE_UNDEF
Reports error on an attempt to expand an undefined shell variable.
The WRDE_APPEND option can be used to append a new set of words to those
generated by a previous call to the wordexp() function. The following
rules apply when two or more calls to the wordexp() function are made
with the same value of the pwordexp parameter and without intervening
calls to the wordfree() function:
· The first such call does not set the WRDE_APPEND option. All
subsequent calls set it.
· For a single invocation of the wordexp() function, all calls either
set the WRDE_DOOFFS option, or do not set it.
· After the second and each subsequent call, the pwordexp parameter
points to a list containing the following:
-- Zero or more null characters, as specified by the WRDE_DOOFFS
option and the we_offs field of the wordexp_t structure.
-- Pointers to the words that were in the pwordexp parameter before
the call, in the same order as before.
-- Pointers to the new words generated by the latest call, in the
specified order.
· The count returned in the pwordexp parameter is the total number of
words from all of the calls.
· The application should not modify the pwordexp parameter between the
calls.
Unless the WRDE_SHOWERR option is set in the flags parameter, the wordexp()
function redirects standard error to /dev/null for any utilities executed
as a result of command substitution while expanding the words parameter. If
the WRDE_SHOWERR option is set, the wordexp() function can write messages
to standard error if syntax errors are detected while expanding the words
parameter.
If any of the following conditions occurs, the wordexp() function returns
the corresponding nonzero constant, which is defined in the wordexp.h file.
[WRDE_BADCHAR]
One of the unquoted characters |, & , ;, <, >, newline, parenthesis,
or braces appears in the words parameter in an inappropriate context.
[WRDE_BADVAL]
Reference to undefined shell variable when the WRDE_UNDEF option is
set in the flags parameter.
[WRDE_CMDSUB]
Command substitution requested when the WRDE_NOCMD option is set in the
flags parameter.
[WRDE_NOSPACE]
An attempt to allocate memory was unsuccessful.
[WRDE_SYNTAX]
Shell syntax error, such as unbalanced parentheses or unterminated
string.
The wordexp() function allows an application to perform all of the shell's
expansions on a word or words obtained from a user. For example, if the
application prompts for a filename (or a list of file names) and then uses
the wordexp() function to process the input, the user could respond with
anything that would be valid as input to the shell.
The WRDE_NOCMD option is provided for applications that, for security or
other reasons, want to prevent a user from executing shell commands.
Disallowing unquoted shell special characters also prevents unwanted side
effects such as executing a command or writing to a file.
NOTES
The wordexp() function can cause a signal to be issued. If a user program
catches the signal, wordexp() may return an error.
RETURN VALUES
If no errors are encountered while expanding the words parameter, the
wordexp() function returns a value of 0 (zero). If an error occurs, the
function returns a nonzero value indicating the error.
If the wordexp() function returns the error value WRDE_NOSPACE, then the
expression in the pwordexp parameter is updated to reflect any words that
were successfully expanded. In other cases, the pwordexp parameter is not
modified.
The wordfree() function returns no value.
FILES
/usr/include/wordexp.h
Defines word expansion macros, data types, and functions.
SEE ALSO
Functions: glob(3)
Standards: standards(5)
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