View source for Bash:Bash-Globbing

=Introduction to globbing=
This short chapter will introduce the concept of [https://en.wikipedia.org/wiki/Glob_(programming) Globbing (wikipedia)].

Globbing is about expressing simple patterns for matching file and directory names. We'll show you by example, so please fire up a terminal and follow the instructions below.

==The operators <code>[]</code>, <code>[!]</code>, <code>?</code>, <code>*</code> and <code>{}</code>==
We will create nine files in your test directory. The files will be empty but created with one single command:
<source lang="Bash">
$ touch file_{1..9}.txt   # {} is specific to bash and actually not part of globbing!
$ ls
file_1.txt  file_3.txt  file_5.txt  file_7.txt  file_9.txt
file_2.txt  file_4.txt  file_6.txt  file_8.txt
</source>
Now, lets learn about the globbing symbol <code>*</code>. A single <code>*</code> means "any number of any characters". The expression <code>[0-9]</code> means "one character which is a number between 0 and 9".

Let's use a combination of <code>*</code> and <code>[0-9]</code>:
<source lang="Bash">
$ ls *_[0-9].txt
#all files that have *_ followed by one digit followed by .txt:
file_1.txt  file_3.txt  file_5.txt  file_7.txt  file_9.txt
file_2.txt  file_4.txt  file_6.txt  file_8.txt
</source>
Next, create a new empty file:
<source lang="Bash">
$ touch file_99.txt
</source>
Let's list all the files which have only one number character after the underscore:
<source lang="Bash">
$ ls *_[0-9].txt  #the file_99.txt file will not be listed!
file_1.txt  file_3.txt  file_5.txt  file_7.txt  file_9.txt
file_2.txt  file_4.txt  file_6.txt  file_8.txt
</source>
As you see, the new file <code>file_99.txt</code> didn't match the globbing expression <code>*_[0-9].txt</code>, since it had more than one number between the underscore and the <code>.txt</code> part.

Now, let's use a globbing expression which will match <code>file_99.txt</code> but not the other files:
<source lang="Bash">
$ ls *_[0-9][0-9].txt
file_99.txt
# The file was listed, because it, and only it,
# had _ followed by two digits followed by .txt
# When we are done playing, remove the newly created text files.
</source>

There is one more operator in globbing, we'd like to show you. It is the <code>?</code> operator which matches "one single character".

<source lang="Bash">
$ touch a.txt ab.txt abc.txt
$ ls ?.txt
a.txt
</source>

<code>?.txt</code> matches one single character followed by ".txt" so a.txt but not "ab.txt", nor "abc.txt" etc.

Finally, we'd like to show you inverted lists. Let's say we have the files <code>file_1.txt  file_3.txt  file_5.txt  file_7.txt  file_9.txt file_2.txt  file_4.txt  file_6.txt  file_8.txt</code>, and we want to match all files in that list, except <code>file_4.txt</code> and <code>file_5.txt</code>.

What we want to express then, is ''all files beginning with "file_" and a character (but not "4" or "5") followed by ".txt"''.

This is what it looks like in globbing (works on Unix-like systems): <code>file_[!4-5].txt</code>:
<source lang="Bash">
$ ls file_[!4-5].txt
file_1.txt  file_3.txt  file_7.txt  file_9.txt
file_2.txt  file_6.txt  file_8.txt
</source>

<noinclude>

=Links=

==Further reading==
* '''https://en.wikipedia.org/wiki/Glob_(programming)'''
* '''http://tldp.org/LDP/abs/html/globbingref.html'''

==Where to go next==
Next chapter is about ''shell expansion''.

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</noinclude>