# Pathname expansion (globbing)

## General

Unlike on other platforms you may have seen, on UNIX(r), the shell is
responsible for interpreting and expanding globs ("filename
wildcards"). A called program will never see the glob itself; it will
only see the expanded filenames as its arguments (here, all filenames
matching `*.log`):

    grep "changes:" *.log

The base syntax for the pathname expansion is the [pattern
matching](../../syntax/pattern.md) syntax. The pattern you describe is matched
against all existing filenames and the matching ones are substituted.
Since this substitution happens **after [word
splitting](../../syntax/expansion/wordsplit.md)**, all resulting filenames are
literal and treated as separate words, no matter how many spaces or
other `IFS`-characters they contain.

## Normal behaviour

-   with [the set command](../../commands/builtin/set.md) (`-f`, `noglob`) you
    can entirely disable pathname expansion
-   when matching a pathname, the slash-character (`/`) always needs to
    be matched explicitly
-   the dot at the beginning of a filename must be matched explicitly
    (also one following a `/` in the glob)
-   a glob that doesn't match a filename is unchanged and remains what
    it is

## Customization

-   when the shell option `nullglob` is set, non-matching globs are
    removed, rather than preserved
-   when the shell option `failglob` is set, non-matching globs produce
    an error message and the current command is not executed
-   when the shell option `nocaseglob` is set, the match is performed
    case-insensitive
-   when the shell option `dotglob` is set, wildcard-characters can
    match a dot at the beginning of a filename
-   when the shell option `dirspell` is set, Bash performs spelling
    corrections when matching directory names
-   when the shell option `globstar` is set, the glob `**` will
    recursively match all files and directories. This glob isn't
    "configurable", i.e. you **can't** do something like `**.c` to
    recursively get all `*.c` filenames.
-   when the shell option `globasciiranges` is set, the bracket-range
    globs (e.g. `[A-Z]`) use C locale order rather than the configured
    locale's order (i.e. `ABC...abc...` instead of e.g. `AaBbCc...`) -
    since 4.3-alpha
-   the variable [GLOBIGNORE](../../syntax/shellvars.md#GLOBIGNORE) can be set
    to a colon-separated list of patterns to be removed from the list
    before it is returned

### nullglob

Normally, when no glob specified matches an existing filename, no
pathname expansion is performed, and the globs are <u>**not**</u>
removed:

    $ echo "Textfiles here:" *.txt
    Textfiles here: *.txt

In this example, no files matched the pattern, so the glob was left
intact (a literal asterisk, followed by dot-txt).

This can be very annoying, for example when you drive a
[for-loop](../../syntax/ccmd/classic_for.md) using the pathname expansion:

    for filename in *.txt; do
      echo "=== BEGIN: $filename ==="
      cat "$filename"
      echo "=== END: $filename ==="
    done

When no file name matches the glob, the loop will not only output stupid
text ("`BEGIN: *.txt`"), but also will make the `cat`-command fail
with an error, since no file named `*.txt` exists.

Now, when the shell option `nullglob` is set, Bash will remove the
entire glob from the command line. In case of the for-loop here, not
even one iteration will be done. It just won't run.

So in our first example:

    $ shopt -s nullglob
    $ echo "Textfiles here:" *.txt
    Textfiles here:

and the glob is gone.

### Glob characters

-   `*` - means \'match any number of characters\'. \'/\' is not matched
    (and depending on your settings, things like \'.\' may or may not be
    matched, see above)
-   `?` - means \'match any single character\'
-   `[abc]` - match any of the characters listed. This syntax also
    supports ranges, like \[0-9\]

For example, to match something beginning with either \'S\' or \'K\'
followed by two numbers, followed by at least 3 more characters:

    [SK][0-9][0-9]???*

## See also

-   [Introduction to expansion and
    substitution](../../syntax/expansion/intro.md)
-   [pattern matching syntax](../../syntax/pattern.md)
-   [the set builtin command](../../commands/builtin/set.md)
-   [the shopt builtin command](../../commands/builtin/shopt.md)
-   [list of shell options](../../internals/shell_options.md)