GLOB(3POSIX)

💖 glob, globfree — GLOB(3POSIX) 💖

okay so this page is from the POSIX Programmer's Manual, and we're talking about glob and globfree, the pathname-matching besties. GLOB(3POSIX) is the manual name, and yes, we're getting into it. 🫶

✨ PROLOG ✨

Real talk, bestie: this manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may differ (so consult the corresponding Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux at all. 💀 Not every platform is gonna have the same vibe.

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🎀 NAME 🎀

glob, globfree — generate pathnames matching a pattern

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💅 SYNOPSIS 💅

#include <glob.h>

int glob(const char *restrict pattern, int flags,
    int(*errfunc)(const char *epath, int eerrno),
    glob_t *restrict pglob);
void globfree(glob_t *pglob);

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🦋 DESCRIPTION 🦋

glob() is a pathname generator, and she shall implement the rules defined in the Shell and Utilities volume of POSIX.1‐2017, Section 2.13, Pattern Matching Notation, with optional support for rule 3 in the Shell and Utilities volume of POSIX.1‐2017, Section 2.13.3, Patterns Used for Filename Expansion. It's giving filename expansion, no cap. ✨

The structure type glob_t is defined in <glob.h> and includes at least the following members:

• size_t gl_pathc — Count of paths matched by pattern.
• char ** gl_pathv — Pointer to a list of matched pathnames.
• size_t gl_offs — Slots to reserve at the beginning of gl_pathv.

The argument pattern is a pointer to a pathname pattern to be expanded. glob() shall match all accessible pathnames against this pattern and develop a list of all pathnames that match. In order to have access to a pathname, glob() requires search permission on every component of a path except the last, and read permission on each directory of any filename component of pattern that contains any of the following special characters: '*', '?', and '['. Permissions check, bestie! 🔐

glob() shall store the number of matched pathnames into pglob->gl_pathc and a pointer to a list of pointers to pathnames into pglob->gl_pathv. The pathnames shall be in sort order as defined by the current setting of the LC_COLLATE category; see the Base Definitions volume of POSIX.1‐2017, Section 7.3.2, LC_COLLATE. The first pointer after the last pathname shall be a null pointer. If the pattern does not match any pathnames, the returned number of matched paths is set to 0, and the contents of pglob->gl_pathv are implementation-defined. Implementation-defined is giving "don't touch it unless you know what you're doing." 🙈

It is the caller's responsibility to create the structure pointed to by pglob. The glob() function shall allocate other space as needed, including the memory pointed to by gl_pathv. The globfree() function shall free any space associated with pglob from a previous call to glob(). So yes, you clean up after yourself, bestie. Periodt. 💅

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

• GLOB_APPEND — Append pathnames generated to the ones from a previous call to glob().
• GLOB_DOOFFS — Make use of pglob->gl_offs. If this flag is set, pglob->gl_offs is used to specify how many null pointers to add to the beginning of pglob->gl_pathv. In other words, pglob->gl_pathv shall point to pglob->gl_offs null pointers, followed by pglob->gl_pathc pathname pointers, followed by a null pointer.
• GLOB_ERR — Cause glob() to return when it encounters a directory that it cannot open or read. Ordinarily, glob() continues to find matches.
• GLOB_MARK — Each pathname that is a directory that matches pattern shall have a <slash> appended.
• GLOB_NOCHECK — Supports rule 3 in the Shell and Utilities volume of POSIX.1‐2017, Section 2.13.3, Patterns Used for Filename Expansion. If pattern does not match any pathname, then glob() shall return a list consisting of only pattern, and the number of matched pathnames is 1.
• GLOB_NOESCAPE — Disable backslash escaping.
• GLOB_NOSORT — Ordinarily, glob() sorts the matching pathnames according to the current setting of the LC_COLLATE category; see the Base Definitions volume of POSIX.1‐2017, Section 7.3.2, LC_COLLATE. When this flag is used, the order of pathnames returned is unspecified.

The GLOB_APPEND flag can be used to append a new set of pathnames to those found in a previous call to glob(). The following rules apply to applications when two or more calls to glob() are made with the same value of pglob and without intervening calls to globfree():

1. The first such call shall not set GLOB_APPEND. All subsequent calls shall set it.
2. All the calls shall set GLOB_DOOFFS, or all shall not set it.
3. After the second call, pglob->gl_pathv points to a list containing the following:
   • Zero or more null pointers, as specified by GLOB_DOOFFS and pglob->gl_offs.
   • Pointers to the pathnames that were in the pglob->gl_pathv list before the call, in the same order as before.
   • Pointers to the new pathnames generated by the second call, in the specified order.
4. The count returned in pglob->gl_pathc shall be the total number of pathnames from the two calls.
5. The application can change any of the fields after a call to glob(). If it does, the application shall reset them to the original value before a subsequent call, using the same pglob value, to globfree() or glob() with the GLOB_APPEND flag.

If, during the search, a directory is encountered that cannot be opened or read and errfunc is not a null pointer, glob() calls (()*errfunc ) with two arguments:

1. The epath argument is a pointer to the path that failed.
2. The eerrno argument is the value of errno from the failure, as set by opendir(), readdir(), or stat(). (Other values may be used to report other errors not explicitly documented for those functions.)

If (()*errfunc ) is called and returns non-zero, or if the GLOB_ERR flag is set in flags, glob() shall stop the scan and return GLOB_ABORTED after setting gl_pathc and gl_pathv in pglob to reflect the paths already scanned. If GLOB_ERR is not set and either errfunc is a null pointer or (()*errfunc ) returns 0, the error shall be ignored. So it can just keep going, lowkey unbothered. 😌

The glob() function shall not fail because of large files. Big files? She said not today. 💅

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💖 RETURN VALUE 💖

Upon successful completion, glob() shall return 0. The argument pglob->gl_pathc shall return the number of matched pathnames and the argument pglob->gl_pathv shall contain a pointer to a null-terminated list of matched and sorted pathnames. However, if pglob->gl_pathc is 0, the content of pglob->gl_pathv is undefined. Undefined, bestie — do not go poking around in there. 🫣

The globfree() function shall not return a value. It's void, periodt.

If glob() terminates due to an error, it shall return one of the non-zero constants defined in <glob.h>. The arguments pglob->gl_pathc and pglob->gl_pathv are still set as defined above. So even when it's messy, you still get partial deets. Iconic. 🌈

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😭 ERRORS 😭

The glob() function shall fail and return the corresponding value if:

• GLOB_ABORTED — The scan was stopped because GLOB_ERR was set or (()*errfunc ) returned non-zero.
• GLOB_NOMATCH — The pattern does not match any existing pathname, and GLOB_NOCHECK was not set in flags.
• GLOB_NOSPACE — An attempt to allocate memory failed.

The following sections are informative.

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🌈 EXAMPLES 🌈

One use of the GLOB_DOOFFS flag is by applications that build an argument list for use with execv(), execve(), or execvp(). Suppose, for example, that an application wants to do the equivalent of:

ls -l *.c

but for some reason:

system("ls -l *.c")

is not acceptable. The application could obtain approximately the same result using the sequence:

globbuf.gl_offs = 2;
glob("*.c", GLOB_DOOFFS, NULL, &globbuf);
globbuf.gl_pathv[0] = "ls";
globbuf.gl_pathv[1] = "-l";
execvp("ls", &globbuf.gl_pathv[0]);

Using the same example:

ls -l *.c *.h

could be approximately simulated using GLOB_APPEND as follows:

globbuf.gl_offs = 2;
glob("*.c", GLOB_DOOFFS, NULL, &globbuf);
glob("*.h", GLOB_DOOFFS|GLOB_APPEND, NULL, &globbuf);
...

That's the whole point of GLOB_DOOFFS and GLOB_APPEND, bestie — making space at the front and adding more matches without starting over. 🫶

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🍓 APPLICATION USAGE 🍓

This function is not provided for the purpose of enabling utilities to perform pathname expansion on their arguments, as this operation is performed by the shell, and utilities are explicitly not expected to redo this. Instead, it is provided for applications that need to do pathname expansion on strings obtained from other sources, such as a pattern typed by a user or read from a file. So don't redo the shell's job, okay? 😭

If a utility needs to see if a pathname matches a given pattern, it can use fnmatch(). That's the dedicated match-checker, iykyk.

Note that gl_pathc and gl_pathv have meaning even if glob() fails. This allows glob() to report partial results in the event of an error. However, if gl_pathc is 0, gl_pathv is unspecified even if glob() did not return an error. Partial results are real, but zero matches means unspecified — don't get it twisted. ✨

The GLOB_NOCHECK option could be used when an application wants to expand a pathname if wildcards are specified, but wants to treat the pattern as just a string otherwise. The sh utility might use this for option-arguments, for example.

The new pathnames generated by a subsequent call with GLOB_APPEND are not sorted together with the previous pathnames. This mirrors the way that the shell handles pathname expansion when multiple expansions are done on a command line. No cap, it's just how the shell does it too. 💅

Applications that need tilde and parameter expansion should use wordexp(). That's the one for the extra expansion sauce. 🎀

🧠 RATIONALE (aka the tea ☕) 🧠

okay so bestie, some people were like, “GLOB_DOOFFS? unnecessary. we can just simulate it, watch:”

           new = (char **)malloc((n + pglob->gl_pathc + 1)
                  * sizeof(char *));
           (void) memcpy(new+n, pglob->gl_pathv,
                  pglob->gl_pathc * sizeof(char *));
           (void) memset(new, 0, n * sizeof(char *));
           free(pglob->gl_pathv);
           pglob->gl_pathv = new;

But that assumes the memory pointed to by gl_pathv is a block that was separately created using malloc(). Not necessarily the case, bestie. An application should make no assumptions about how the memory referenced by fields in pglob was allocated. It might have been obtained from malloc() in a large chunk and then carved up within glob(), or it might have been created using a different memory allocator. It is not the intent of the standard developers to specify or imply how the memory used by glob() is managed. Periodt. 💅

The GLOB_APPEND flag would be used when an application wants to expand several different patterns into a single list. That’s the vibe. ✨

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🔮 FUTURE DIRECTIONS 🔮

None. That’s it. Nothing. The future is a blankie. 💀

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👀 SEE ALSO 👀

• exec
• fdopendir()
• fnmatch()
• fstatat()
• readdir()
• Section 2.6, Word Expansions
• The Base Definitions volume of POSIX.1‐2017, Section 7.3.2, LC_COLLATE, <glob.h>

iykyk 🫶

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📜 COPYRIGHT 📜

Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1-2017, Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 7, 2018 Edition, Copyright (C) 2018 by the Institute of Electrical and Electronics Engineers, Inc and The Open Group.

In the event of any discrepancy between this version and the original IEEE and The Open Group Standard, the original IEEE and The Open Group Standard is the referee document. The original Standard can be obtained online at http://www.opengroup.org/unix/online.html .

Any typographical or formatting errors that appear in this page are most likely to have been introduced during the conversion of the source files to man page format. To report such errors, see https://www.kernel.org/doc/man-pages/reporting_bugs.html .

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okay bye bestie! this was GLOB(3POSIX) from IEEE/The Open Group, 2017. stay slaying those globs 💅✨🫶