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Related to https://github.com/flokoe/bash-hackers-wiki/issues/10
115 lines
4.3 KiB
Markdown
115 lines
4.3 KiB
Markdown
# Pathname expansion (globbing)
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## General
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Unlike on other platforms you may have seen, on UNIX(r), the shell is
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responsible for interpreting and expanding globs (\"filename
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wildcards\"). A called program will never see the glob itself; it will
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only see the expanded filenames as its arguments (here, all filenames
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matching `*.log`):
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grep "changes:" *.log
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The base syntax for the pathname expansion is the [pattern
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matching](../../syntax/pattern.md) syntax. The pattern you describe is matched
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against all existing filenames and the matching ones are substituted.
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Since this substitution happens **after [word
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splitting](../../syntax/expansion/wordsplit.md)**, all resulting filenames are
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literal and treated as separate words, no matter how many spaces or
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other `IFS`-characters they contain.
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## Normal behaviour
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- with [the set command](../../commands/builtin/set.md) (`-f`, `noglob`) you
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can entirely disable pathname expansion
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- when matching a pathname, the slash-character (`/`) always needs to
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be matched explicitly
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- the dot at the beginning of a filename must be matched explicitly
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(also one following a `/` in the glob)
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- a glob that doesn\'t match a filename is unchanged and remains what
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it is
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## Customization
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- when the shell option `nullglob` is set, non-matching globs are
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removed, rather than preserved
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- when the shell option `failglob` is set, non-matching globs produce
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an error message and the current command is not executed
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- when the shell option `nocaseglob` is set, the match is performed
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case-insensitive
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- when the shell option `dotglob` is set, wildcard-characters can
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match a dot at the beginning of a filename
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- when the shell option `dirspell` is set, Bash performs spelling
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corrections when matching directory names
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- when the shell option `globstar` is set, the glob `**` will
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recursively match all files and directories. This glob isn\'t
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\"configurable\", i.e. you **can\'t** do something like `**.c` to
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recursively get all `*.c` filenames.
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- when the shell option `globasciiranges` is set, the bracket-range
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globs (e.g. `[A-Z]`) use C locale order rather than the configured
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locale\'s order (i.e. `ABC...abc...` instead of e.g. `AaBbCc...`) -
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since 4.3-alpha
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- the variable [GLOBIGNORE](../../syntax/shellvars.md#GLOBIGNORE) can be set
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to a colon-separated list of patterns to be removed from the list
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before it is returned
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### nullglob
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Normally, when no glob specified matches an existing filename, no
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pathname expansion is performed, and the globs are [**not**]{.underline}
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removed:
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$ echo "Textfiles here:" *.txt
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Textfiles here: *.txt
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In this example, no files matched the pattern, so the glob was left
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intact (a literal asterisk, followed by dot-txt).
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This can be very annoying, for example when you drive a
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[for-loop](../../syntax/ccmd/classic_for.md) using the pathname expansion:
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for filename in *.txt; do
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echo "=== BEGIN: $filename ==="
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cat "$filename"
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echo "=== END: $filename ==="
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done
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When no file name matches the glob, the loop will not only output stupid
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text (\"`BEGIN: *.txt`\"), but also will make the `cat`-command fail
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with an error, since no file named `*.txt` exists.
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Now, when the shell option `nullglob` is set, Bash will remove the
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entire glob from the command line. In case of the for-loop here, not
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even one iteration will be done. It just won\'t run.
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So in our first example:
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$ shopt -s nullglob
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$ echo "Textfiles here:" *.txt
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Textfiles here:
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and the glob is gone.
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### Glob characters
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- \* - means \'match any number of characters\'. \'/\' is not matched
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(and depending on your settings, things like \'.\' may or may not be
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matched, see above)
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- ? - means \'match any single character\'
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- \[abc\] - match any of the characters listed. This syntax also
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supports ranges, like \[0-9\]
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For example, to match something beginning with either \'S\' or \'K\'
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followed by two numbers, followed by at least 3 more characters:
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[SK][0-9][0-9]???*
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## See also
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- [Introduction to expansion and
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substitution](../../syntax/expansion/intro.md)
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- [pattern matching syntax](../../syntax/pattern.md)
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- [the set builtin command](../../commands/builtin/set.md)
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- [the shopt builtin command](../../commands/builtin/shopt.md)
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- [list of shell options](../../internals/shell_options.md)
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