If for any reason you need to find where in the disk a command, you may use which this command will search on the PATH and display the directory where the command is located.

You may also look for a list of commands instead of a simple command, lets see some examples: <p class="codigo">which ls</p>

The output is:

/bin/ls

Now if you run:

which opera

This is the output in my PC, where I have opera installed.

/usr/bin/opera

But, you can also run which to look for a list of commands as I said before.

which ls opera

This might be the output:

/bin/ls
/usr/bin/opera

For more information, see the man pages.