Unit 9: Pattern Matching in bash
We now show you another productivity shortcut. In an example earlier, you have seen how we passed in more than one file names into cat. Recall that we can use Tab to auto-complete the file names, so we can hit fewer keys on the keyboards.
Now, we show you there is an even faster way.
Instead of
$ cat test.txt foo.txt bar.txt | wc
We could just run
$ cat *.txt | wc
The * is a special character in bash that represents 0 or more characters. So, this command essentially says, cat any files that contain 0 or more characters, followed by .txt.
The table below summarizes the useful patterns:
| Pattern | Matches |
|---|---|
* |
0 or more characters |
? |
one character |
[..] |
one character, coming from the given set between [ and ], - to indicate a range. |
{.., ..} |
Either one of the names, separated by ,. |
Example 1:
$ ls ???.txt
bar.txt foo.txt
Since we use three ?, it matches any file name with three characters followed by .txt.
Example 2:
$ ls [f-t]*t
foo.txt test.txt
The expression [f-t]*t matches all file names the start with alphabet f, g, etc, until t, followed by zero or more characters, followed by t.
Example 3:
$ ls *.txt
bar.txt foo.txt test.txt
$ ls {fo,ba}??txt
bar.txt foo.txt
The expression {fo,ba}??txt matches any file names the start with either fo or ba, followed by two characters, followed by txt.