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wordexp (3)

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NAME

wordexp, wordfree - perform word expansions

SYNOPSIS

#include <wordexp.h>

int wordexp(const char *restrict words, wordexp_t *restrict pwordexp,
    int flags);

void wordfree(wordexp_t *pwordexp);

DESCRIPTION

The wordexp() function performs word expansions, subject to quoting, and places the list of expanded words into the structure pointed to by pwordexp.

The wordfree() function frees any memory allocated by wordexp() associated with pwordexp.

words Argument

The words argument is a pointer to a string containing one or more words to be expanded. The expansions will be the same as would be performed by the shell if words were the part of a command line representing the arguments to a utility. Therefore, words must not contain an unquoted NEWLINE or any of the unquoted shell special characters:

| & ; < >

except in the context of command substitution. It also must not contain unquoted parentheses or braces, except in the context of command or variable substitution. If the argument words contains an unquoted comment character (number sign) that is the beginning of a token, wordexp() may treat the comment character as a regular character, or may interpret it as a comment indicator and ignore the remainder of words.

pwordexp Argument

The structure type wordexp_t is defined in the header <wordexp.h> and includes at least the following members:

size_t we_wordc

: Count of words matched by words.

char **we_wordv

: Pointer to list of expanded words.

size_t we_offs

: Slots to reserve at the beginning of pwordexp->we_wordv.

The wordexp() function stores the number of generated words into pwordexp->we_wordc and a pointer to a list of pointers to words in pwordexp->we_wordv. Each individual field created during field splitting is a separate word in the pwordexp->we_wordv list. The words are in order. The first pointer after the last word pointer will be a null pointer.

It is the caller's responsibility to allocate the storage pointed to by pwordexp. The wordexp() function allocates other space as needed, including memory pointed to by pwordexp->we_wordv. The wordfree() function frees any memory associated with pwordexp from a previous call to wordexp().

flags Argument

The flags argument is used to control the behavior of wordexp(). The value of flags is the bitwise inclusive OR of zero or more of the following constants, which are defined in <wordexp.h>:

WRDE_APPEND

: Append words generated to the ones from a previous call to wordexp().

WRDE_DOOFFS

: Make use of pwordexp->we_offs. If this flag is set, pwordexp->we_offs is used to specify how many NULL pointers to add to the beginning of pwordexp->we_wordv. In other words, pwordexp->we_wordv will point to pwordexp->we_offs NULL pointers, followed by pwordexp->we_wordc word pointers, followed by a NULL pointer.

WRDE_NOCMD

: Fail if command substitution is requested.

WRDE_REUSE

: The pwordexp argument was passed to a previous successful call to wordexp(), and has not been passed to wordfree(). The result will be the same as if the application had called wordfree() and then called wordexp() without WRDE_REUSE.

WRDE_SHOWERR

: Do not redirect stderr to /dev/null.

WRDE_UNDEF

: Report error on an attempt to expand an undefined shell variable.

The WRDE_APPEND flag can be used to append a new set of words to those generated by a previous call to wordexp(). The following rules apply when two or more calls to wordexp() are made with the same value of pwordexp and without intervening calls to wordfree():

1.: The first such call must not set WRDE_APPEND. All subsequent calls must set it.

2.: All of the calls must set WRDE_DOOFFS, or all must not set it.

3.

After the second and each subsequent call, pwordexp->we_wordv will point to a list containing the following:

a.: zero or more NULL pointers, as specified by WRDE_DOOFFS and pwordexp->we_offs.

b.: pointers to the words that were in the pwordexp->we_wordv list before the call, in the same order as before.

c.: pointers to the new words generated by the latest call, in the specified order.

4.: The count returned in pwordexp->we_wordc will be the total number of words from all of the calls.

5.: The application can change any of the fields after a call to wordexp(), but if it does it must reset them to the original value before a subsequent call, using the same pwordexp value, to wordfree() or wordexp() with the WRDE_APPEND or WRDE_REUSE flag.

If words contains an unquoted:

NEWLINE | & ; < > ( ) { }

in an inappropriate context, wordexp() will fail, and the number of expanded words will be zero.

Unless WRDE_SHOWERR is set in flags, wordexp() will redirect stderr to /dev/null for any utilities executed as a result of command substitution while expanding words.

If WRDE_SHOWERR is set, wordexp() may write messages to stderr if syntax errors are detected while expanding words. If WRDE_DOOFFS is set, then pwordexp-> we_offs must have the same value for each wordexp() call and wordfree() call using a given pwordexp.

The following constants are defined as error return values:

WRDE_BADCHAR

One of the unquoted characters:

NEWLINE | & ; < > ( ) { }

appears in words in an inappropriate context.

WRDE_BADVAL

: Reference to undefined shell variable when WRDE_UNDEF is set in flags.

WRDE_CMDSUB

: Command substitution requested when WRDE_NOCMD was set in flags.

WRDE_NOSPACE

: Attempt to allocate memory failed.

WRDE_SYNTAX

: Shell syntax error, such as unbalanced parentheses or unterminated string.

RETURN VALUES

On successful completion, wordexp() returns 0.

Otherwise, a non-zero value as described in <wordexp.h> is returned to indicate an error. If wordexp() returns the value WRDE_NOSPACE, then pwordexp->we_wordc and pwordexp->we_wordv will be updated to reflect any words that were successfully expanded. In other cases, they will not be modified.

The wordfree() function returns no value.

ERRORS

No errors are defined.

USAGE

This function is intended to be used by an application that wants to do 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 list of filenames) and then uses wordexp() to process the input, the user could respond with anything that would be valid as input to the shell.

The WRDE_NOCMD flag is provided for applications that, for security or other reasons, want to prevent a user from executing shell command. Disallowing unquoted shell special characters also prevents unwanted side effects such as executing a command or writing a file.