Linux - Backtik Operator - Return the result of a command as a parameter for another.

Linux has many useful features which make work easier. While managing packages I often find myself trying to run commands like yum remove but can't remember the exact version numbers, character case, or exact spelling. Usually the solution is to run rpm -qa | grep -i . For example:

$ rpm -qa | grep -i virtualbox

This would yield:

VirtualBox-4.1-4.1.0_73009_fedora14-1.x86_64

Try remembering how to type that package name every time you want to upgrade an RPM with yum.

Wouldn't it be nice to be able to combine both "yum remove" and "rpm -qa..." Linux offers this capability through the back-tick operator. ``. What it does is simply returns the output of the command executed within it. This enables the output to be passed as a parameter to some other command.

# yum remove `rpm -qa | grep -i virtualbox`

Yum will then nicely ask if you wish to remove the above mentioned program. Imagine the possibilities.  

WARNING: Be careful if you use this to remove packages from your system.  I only have one package called virtualbox installed on the system, but if you type in some other package name like "pl" you could end up in a lot of trouble.  Double check what your system is trying to remove.

For example:

# yum remove `rpm -qa | grep -i pl`

My system tells me it will remove 693 packages using 4.5GB of space, and is asking me if I want to continue.  That's nearly all my supporting packages.

Basically, use the backtick operator to your heart's content, but be very wary when cross scripting with commands such as 'yum remove'.