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Another trick I like is to turn on line numbers. This is useful, especially if an error 
message in a log file is complaining about a file regarding a specific line. The 
following command turns on line numbers:
:set number
The following command disables line numbers:
:set nonumber
If you'd always like to see line numbers by default, you can edit the 
.vimrc
 file inside 
your home directory. This file is read by 
vim
 each time you start it.
Go ahead and open the 
.vimrc
 file in your editor:
vim ~/.vimrc
Most likely, this will be a blank file for you as a 
.vimrc
 file doesn't exist by default. 
There are many commands we can add to tweak the behavior of the 
vim
 editor, too 
many to mention in a single chapter. The following line is very useful though, as it 
ensures that line numbers are enabled by default:
set number
Leaving out the colon at the beginning of the line is intentional; it's not required 
inside the 
.vimrc
 file. From this point forward, each new 
vim
 session you open will 
start off with line numbers enabled. You can still disable line numbers as needed 
with the 
:set nonumber
 command within 
vim
 as we did earlier. In addition, you can 
add many more customizations to 
vim
 with the 
.vimrc
 file, but that's beyond the 
scope of this chapter. For now, just know that the possibility of customizing 
vim
 with 
the config file is something that you can do.
Now that we know how to edit files, we should also take a closer look at streams, 
which allow us to manipulate both input and output in various ways.
Note that the 
.vimrc
 file begins with a period, which means that 
the file is hidden. Hidden files aren't normally shown to you when 
you use 
ls
 to list the contents of a directory. Using the 
-a
 option 
with the 
ls
 command will show all files, including the ones that 
are normally hidden.

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Managing Files and Directories