Wednesday Why: Colour ls

$ ls -l /etc/sysconfig

auditd authconfig autofs bittorrent bluetooth cbq clock console cpuspeed crond dund firstboot grub hidd hsqldb

httpd hwconf hw-uuid i18n init ip6tables-config iptables-config irda irqbalance kernel keyboard kudzu libvirtd lirc livna-config-display

lm_sensors modules nasd netconsole network networking network-scripts ntpd oidentd pand prelink readonly-root samba saslauthd selinux

sendmail smartmontools spamassassin squid syslog system-config-securitylevel system-config-users tux vdr vdr-plugins.d vncservers wpa_supplicant xendomains xinetd

Notice that cbq, console, modules, networking, network-scripts and vdr-plugins.d are all in blue (indicating a directory); libvirtd and xendomains are in green (indicating an executable file); and selinux is in turquoise (indicating a valid symbolic link).

The ls output is in colour because ls is actually an alias:

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

When ls is executed, the option --color=tty is automatically added (note to those in Commonwealth countries: color option has no u here!).

The actual colour associations are contained in the environment variable LS_COLORS, which is set by the script /etc/profile.d/colorls.sh (or colorls.csh if you use csh). This script, which is also responsible for setting up the ls alias, gets the colors from one of several possible configuration files; these are from highest to lowest priority: ~/.dir_colors.$TERM, ~/.dir_colors, ~/.dircolors.$TERM, ~/.dircolors, /etc/DIR_COLORS.$TERM, or /etc/DIR_COLORS (where $TERM is your current terminal type as specified by the TERM environment variable).

All that to say that unless you've customized your system, your ls colours are specified in /etc/DIR_COLORS.xterm and /etc/DIR_COLORS, depending on whether you're using an xterm-compatible terminal window or a virtual console.

The /etc/DIR_COLORS.xterm file contains these lines:

# Below are the color init strings for the basic file types. A color init
# string consists of one or more of the following numeric codes:
# Attribute codes:
# 00=none 01=bold 04=underscore 05=blink 07=reverse 08=concealed
# Text color codes:
# 30=black 31=red 32=green 33=yellow 34=blue 35=magenta 36=cyan 37=white
# Background color codes:
# 40=black 41=red 42=green 43=yellow 44=blue 45=magenta 46=cyan 47=white
NORMAL 00 # global default, although everything should be something.
FILE 00 # normal file
DIR 01;34 # directory
LINK 01;36 # symbolic link
FIFO 40;33 # pipe
SOCK 01;35 # socket
BLK 40;33;01 # block device driver
CHR 40;33;01 # character device driver
ORPHAN 01;05;37;41 # orphaned syminks
MISSING 01;05;37;41 # ... and the files they point to

# This is for files with execute permission:
EXEC 01;32

# List any file extensions like '.gz' or '.tar' that you would like ls
# to colorize below. Put the extension, a space, and the color init string.
# (and any comments you want to add after a '#')
.cmd 01;32 # executables (bright green)
.exe 01;32
.com 01;32
.btm 01;32
.bat 01;32
.sh 01;32
.csh 01;32
.tar 01;31 # archives or compressed (bright red)
.tgz 01;31
.arj 01;31
.taz 01;31

(...lines snipped...)

As you can see, each file type or extension is matched up with a corresponding list of attributes and colors to be used. The color and attribute codes are listed in the comments within this file.

You can easily make a personal copy of this file and modify it to suit your needs:

$ cp /etc/DIR_COLORS.xterm ~/.dir_colors.xterm

If you wanted to show .doc files in white-on-magenta, for example, add this line to ~/.dir_colors.xterm:

.doc 01;37;45

Since 01 is the attribute code for bold, 37 is a white foreground, and 45 is a magenta background.