Command auto-completion

[Guest anon]

Written by Tom Berger

What is the shortest way to switch your current working directory from your home directory to the directory '/usr/src/linux/Documentation/isdn/' using the 'cd' ('change directory') command????

 

It's

cd /u<TAB>sr<TAB>l<TAB>/D<TAB>is<TAB>

 

This is called 'automatic command line completion' and it is indispensable. Let's have a closer look at the example:

 

cd /u<TAB>

 

expands to cd /usr/. Easy. Next

 

cd /u<TAB>sr<TAB>

 

expands to cd /usr/src/. If you just enter cd /u<TAB>s<TAB>, you will be presented with a choice of three subdirectories of '/usr' which all match this pattern ('cd /u*/s*'): '/usr/sbin', '/usr/share' and '/usr/src'.

 

So the <TAB> key is a handy means to search directories for files or subdirectories you know the first letters of. For example ls /usr/bin/zip<TAB> gives you a list of all files and subdirectories in '/usr/bin' that start with the letters 'zip'. Of course there are much more powerful commands for this tasks, but it does the trick when you're in a hurry.

Furthermore it comes in handy with really long filenames. Say you want to install an RPM called 'boomshakalakwhizbang-4.6.4.5-mdk586.rpm'. You type rpm -i boom<TAB> and if there are no other files in this directory that match this pattern, the shell will fill in the rest by itself.

 

cd /u<TAB>sr<TAB>l<TAB>

 

expands to cd /usr/src/linux and waits for a decision. There are two directories in '/usr/src' that match: '/usr/src/linux-[...]' and '/usr/src/linux'. How do you tell the shell you want the latter? Append a slash ('/'), thus indicating the end of this last name.

Presume you are not sure if it was '/usr/src/linux/Documentation' or '/usr/src/linux/documentation'. As you may know, Linux discriminates between upper and lower case. If you have read carefully until here, you know the answer already:

 

cd /u<TAB>sr<TAB>l<TAB>/d<TAB>

 

expands to '/usr/src/linux/drivers/'. Looks like it was 'Documentation' (with a capital 'D') then.

 

This kind of completion works for commands, too:

 

[tom@belbo tom]$ gre<TAB>

grecord grefer grep

[tom@belbo tom]$ gre

 

Here the shell presents me with a list of all the commands it knows about which start with the string 'gre'.