UNIX for Beginners Questions & Answers

Is there a "gray area" between grepping and globbing?
A moment ago I just read that "The moral of the story is that grep never uses globbing." (see link)
I also thought I had it straight in my mind that globbing is for filenames, and grepping is for searching text within a file.
Yet my first post above asks for help grepping filenames!

Globbing and Regex: So Similar, So Different | Linux Journal

In your post, you're not "grepping filenames", but grepping text that is the result of an ls command, containing file names.


As you pointed out, you need to differentiate between "grepping and globbing", which are not the same even though it sometimes may seem so. Either is a malapropism; the exact terms would be "regex matching" and "pattern matching".

"Globbing" deals with patterns and is done by the shell, mostly when dealing with directory contents. And, in one exceptional case, some recent shells can deal with regexes: in "conditional expressions". man bash: "Grepping" deals with regexes, basic and extended, abbr. BREs and EREs. They have many subtleties, and it pays off to spend some time reading the man page.

Patterns and regexes in principle have different syntaxes. There are some overlaps, e.g. the [...] bracket expression meaning "Match any one of the enclosed characters", but also "faux amis" (false friends) like the * . It's always annoying to keep those differences in mind when dealing with either, and I have to test and experiment every single time when I switch from one to the other.

With regards to pattern matching, perhaps a finer point to be made here is that (standard) globbing, or glob pattern matching, is a special form of pattern matching, where patterns are used for filename expansion.

In pattern matching, the wildcards are *, ? or a bracket expression ( [ ... ] )

In the case of globbing there are the following extra rules:

Globbing results in a list of files if there is a match, or the pattern itself if there is no match. The order in which the list of files is presented is governed by LC_COLLATE.
See Patterns Used for Filename Expansion


Examples:

Code:

$ mkdir -p somedir/foo
$ touch a.b .a.b somedir/bar somedir/.baz somedir/"foo bar"
$ ls -d *
a.b	somedir
$ ls -d .*
.	..	.a.b
$ ls -d * .*
.	..	.a.b	a.b	somedir
$ ls -d * .[!.]*
.a.b	a.b	somedir
$ ls -d */*
somedir/bar	somedir/foo	somedir/foo bar

Compare this to regular pattern matching, where a slash is actually matched

Code:

$ ls -d somedir/foo | while read line; do case $line in (*) echo "$line"; esac; done
somedir/foo

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The bash shell and other more modern shells, like ksh93 and zsh also support extended globbing with additional rules.