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10.4.2 Calling wordexp

All the functions, constants and data types for word expansion are declared in the header file wordexp.h.

Word expansion produces a vector of words (strings). To return this vector, wordexp uses a special data type, wordexp_t, which is a structure. You pass wordexp the address of the structure, and it fills in the structure’s fields to tell you about the results.

Data Type: wordexp_t ¶

This data type holds a pointer to a word vector. More precisely, it records both the address of the word vector and its size.

we_wordc

The number of elements in the vector.

we_wordv

The address of the vector. This field has type char **.

we_offs

The offset of the first real element of the vector, from its nominal address in the we_wordv field. Unlike the other fields, this is always an input to wordexp, rather than an output from it.

If you use a nonzero offset, then that many elements at the beginning of the vector are left empty. (The wordexp function fills them with null pointers.)

The we_offs field is meaningful only if you use the WRDE_DOOFFS flag. Otherwise, the offset is always zero regardless of what is in this field, and the first real element comes at the beginning of the vector.

Function: int wordexp (const char *words, wordexp_t *word-vector-ptr, int flags) ¶

Preliminary: | MT-Unsafe race:utent const:env env sig:ALRM timer locale | AS-Unsafe dlopen plugin i18n heap corrupt lock | AC-Unsafe corrupt lock fd mem | See POSIX Safety Concepts.

Perform word expansion on the string words, putting the result in a newly allocated vector, and store the size and address of this vector into *word-vector-ptr. The argument flags is a combination of bit flags; see Flags for Word Expansion, for details of the flags.

You shouldn’t use any of the characters ‘|&;<>’ in the string words unless they are quoted; likewise for newline. If you use these characters unquoted, you will get the WRDE_BADCHAR error code. Don’t use parentheses or braces unless they are quoted or part of a word expansion construct. If you use quotation characters ‘'"`’, they should come in pairs that balance.

The results of word expansion are a sequence of words. The function wordexp allocates a string for each resulting word, then allocates a vector of type char ** to store the addresses of these strings. The last element of the vector is a null pointer. This vector is called the word vector.

To return this vector, wordexp stores both its address and its length (number of elements, not counting the terminating null pointer) into *word-vector-ptr.

If wordexp succeeds, it returns 0. Otherwise, it returns one of these error codes:

WRDE_BADCHAR ¶

The input string words contains an unquoted invalid character such as ‘|’.

WRDE_BADVAL ¶

The input string refers to an undefined shell variable, and you used the flag WRDE_UNDEF to forbid such references.

WRDE_CMDSUB ¶

The input string uses command substitution, and you used the flag WRDE_NOCMD to forbid command substitution.

WRDE_NOSPACE ¶

It was impossible to allocate memory to hold the result. In this case, wordexp can store part of the results—as much as it could allocate room for.

WRDE_SYNTAX ¶

There was a syntax error in the input string. For example, an unmatched quoting character is a syntax error. This error code is also used to signal division by zero and overflow in arithmetic expansion.

Function: void wordfree (wordexp_t *word-vector-ptr) ¶

Preliminary: | MT-Safe | AS-Unsafe corrupt heap | AC-Unsafe corrupt mem | See POSIX Safety Concepts.

Free the storage used for the word-strings and vector that *word-vector-ptr points to. This does not free the structure *word-vector-ptr itself—only the other data it points to.