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Hack 15. Colorize Files in Your Pager

As a Linux user you might have noticed that filenames appear in
different colors when you type ls or
dir. Yet when you pipe the colored file listing
through a pager such as less, the pager ignores
the colors and turns the output into black and white. You might
notice this when you execute a commonly used command, such as
ls -al | less.

Most Linux distributions are configured to display the files in
various colors to make it easy to identify symbolic links, executable
files, compressed files, and so on. If yours is not configured in
such a way, there's an easy way to correct this.
Type the following command:

$ alias ls='ls --color=auto'

This tells your system that every time you type the
ls command, it will actually type ls
--color=auto for you. Now type the command:

$ ls

You should see your files appear in different colors, according to
their type. If you didn't see colored filenames, you
might have a distribution that requires a slightly different switch.
Try this instead:

$ alias ls='ls --color=tty'

Now type the command to test the color capability:

$ ls

Chances are that one or more alias definitions are
already defined for you in one of the automatically executed login
files. See the sidebar Bash Auto-Configuration Files
for more information about how many popular distributions make these
settings.

2.7.1. The Black-and-White Problem

Now here's the problem that might plague you at
times. You want to view a list of files, so you issue the command
ls -a. That command lists all
the regular and hidden files, and all the files and directories
appear in living color. Or perhaps you prefer to use the command
ls -al that lists all regular
and hidden files in a detailed single column. Once again, the files
appear in living color.

When there are many files, the list scrolls off the screen. This is
particularly troublesome on a text console that
doesn't let you scroll back far enough to see the
beginning of the list. What's a geek to do? The
intuitive solution is to issue this command:

$ ls -al | less

This pipes the output of ls -al tHRough the
less pager, which lets you scroll back and forth
through the entire output of the ls -al command.

There's just one catch. All the pretty colors are
gone. It is no longer easy to identify compressed files from
executable files (and so on...) at a glance.

You don't see colors in the
less pager for two reasons. First,
less requires the -R
command-line switch to display colors. That
won't be enough for most Linux users, however. You
can find out for yourself if adding the -R switch
is all you need for your Linux distribution by typing this command:

$ ls -al | less -R

Did you see the list of files in color? Probably not.
That's because most Linux distributions set up
ls as an alias for the command ls
--color=tty or ls --color=auto. These
commands output color only when the destination is a terminal screen.
When you pipe the output or redirect the output from
ls, it turns off the color feature automatically.

There are at least three solutions to this problem.

2.7.2. Solution 1

Here's one way to fix the problem. The ls
--color command does not care what the output is, whether
it's a terminal screen, a redirection to another
file, or a pipe to another program. One or more files in your system
contain the commands to set the aliases (see the sidebar Bash Auto-Configuration Files, which includes information
on where these settings are made for various distributions). Find the
file on your system where you want to change the way the aliases are
set. Look for the line that defines the color as
auto or tty as the default,
and change it to this (you might as well add the
-R to less while
you're at it):

alias ls='ls --color'
alias less='less -R'

By not specifying tty or
auto, the ls command will
output color no matter where the output is directed.

There's a catch to doing things this way, so before
you edit the file that defines the alias command, try the technique
manually so that you can see for yourself what the catch will be.
Follow these steps to set the default behavior for both
ls and less to support color,
and then perform the piped output command to see a listing of files
in color:

$ alias ls='ls --color'
$ alias less='less -R'
$ ls -al | less

There you gocolorized output in the less
pager.

Now that ls automatically outputs color no matter
where the output is directed, try this command to redirect the output
of the colored directory list to a file:

$ ls -al > directory.txt

Now open the file with your favorite editor, and you should see all
the codes used to colorize the text. For example, you might see
something like this:

[[01;34mDesktop[[00m
[[01;31mEiosource-1.1-1.i386.rpm[[00m
[[01;34mGNUstep[[00m
[[00mHello[[00m
[[00mKernel-Win4Lin3-2.6.6.patch[[00m

Your editor doesn't interpret the codes to colorize
your text. It simply shows you the codes that exist in the output of
the command. This is not quite what you want when you redirect output
to a file, is it?

So, here's a way to deal with the first solution.
You can modify your alias settings so that the following command
produces colorized output:

$ ls -al | less

When you don't want to produce colorized output,
such as when you want to redirect the output to a file, you override
the alias with a command like this, which specifies that
ls should output color only if the destination is
a terminal:

$ ls -al --color=auto > directory.txt

2.7.3. Solution 2

The second solution is precisely the opposite of the first. Leave the
alias alone, as it is already set. When you get the hankering to view
a long directory list through a pager, override the setting that
restricts color output to terminals with this command:

$ ls -al --color | less -R

2.7.4. Solution 3

Neither of the previous solutions is the "Linux
way"; that is, a way to customize and automate
everything. So, here's a way to solve the problem
like a true Linux hacker would. Define aliases to give you the
choices you want while using shorthand commands.
Here's one example, but it is by no means the only
way to approach this. Edit the file where aliases are defined so that
it contains these aliases:

alias ls='ls --color=auto'
alias lsp='ls --color | less -R'
alias dir='ls -al'
alias dirp='ls -al --color | less -R'

This way, you can issue a command such as ls -al >
directory.txt, and the file won't be
littered with color codes. Yet anytime you want to page through a
full list of your files in living color, all you have to type is the
command lsp or dirp.

alias l.='ls -d .* --color=tty'
alias ll='ls -l --color=tty'
alias ls='ls --color=tty'

alias ls='ls --color=auto'

alias ls='ls --color=tty'

alias ls='--color=auto'

alias ls="ls --color=auto"