Set Practical ls Colours with a dir_colors File

Your directory listing is one flat colour and the log files you care about hide in it. You will write a small, user-owned dir_colors file that gives directories and log files clear colours, then load it into LS_COLORS with one shell command. It takes about ten minutes and targets GNU dircolors 9.4 from GNU coreutils, with the dir_colors(5) format documented by Linux man-pages 6.7.

• You need: GNU dircolors, ls and a shell. No elevated privileges.
• What it touches: your shell environment and directory listings, never the files being listed.

1. Check the installed tools

Start with read-only checks. They confirm which implementation will parse the file, so you do not end up debugging a different command earlier in your PATH:

$ command -v dircolors
/usr/bin/dircolors
$ dircolors --version
dircolors (GNU coreutils) 9.4
$ command -v ls
/usr/bin/ls

Your paths or version may differ. The GNU implementation is the detail that matters. The manual also describes statements accepted by Slackware's implementation, but GNU dircolors ignores its COLOR, OPTIONS and EIGHTBIT statements.

2. Make a minimal configuration

Choose a user-owned path. The manual names /etc/DIR_COLORS and ~/.dir_colors as conventional locations, but says GNU dircolors ignores them on Debian. Passing the path explicitly makes the source of your settings unambiguous.

First check whether a file already exists. This is read-only:

$ test -e "$HOME/.dir_colors" && ls -l "$HOME/.dir_colors" || echo 'no existing user file'

If it exists and holds settings you want to keep, copy it before editing. The original is untouched:

$ cp --preserve=mode,ownership,timestamps "$HOME/.dir_colors" "$HOME/.dir_colors.bak"

$ cat > "$HOME/.dir_colors" <<'EOF'
# Global rules apply to every terminal type.
NORMAL 0
DIR 01;34
*.log 01;31

# This rule is used when TERM matches this pattern.
TERM xterm-256color
DIR 01;36
EOF

How the file is read:

• Blank lines are ignored, and text after a hash preceded by whitespace is a comment.
• Statements are case-insensitive.
• Scope: a statement before the first TERM is global. Later statements belong to the matching terminal section.
• Overrides: a later terminal-specific declaration can override a global one.

$ sed -n '1,80p' "$HOME/.dir_colors"
# Global rules apply to every terminal type.
NORMAL 0
DIR 01;34
*.log 01;31

# This rule is used when TERM matches this pattern.
TERM xterm-256color
DIR 01;36

3. Generate LS_COLORS for the current shell

GNU dircolors reads the file and prints shell code. Use -b for Bourne-style shells such as Bash, Dash and Zsh:

$ eval "$(dircolors -b "$HOME/.dir_colors")"
$ printf '%s\n' "$LS_COLORS"
no=0:di=01;34:*.log=01;31:di=01;36:

The exact order and terminal-specific entries depend on TERM. The final di=01;36 is the matching terminal rule overriding the earlier directory rule, which happens when this terminal is xterm-256color. A generated fragment normally holds an LS_COLORS assignment and an export.

Test the result without forcing colour into a log or pipe:

$ mkdir -p /tmp/dir-colors-check
$ touch /tmp/dir-colors-check/example.log /tmp/dir-colors-check/notes.txt
$ ls --color=auto -l /tmp/dir-colors-check
total 0
-rw-r--r-- 1 ... example.log
-rw-r--r-- 1 ... notes.txt

Ownership, timestamps and spacing vary. In an interactive terminal, example.log and the directory name should use the configured styles. The automatic colour option emits colour for a terminal but avoids escape sequences when output is redirected.

4. Load the file automatically, carefully

Once the manual command works, add it to the startup file for the shell you actually use. For Bash, put this line in ~/.bashrc:

eval "$(dircolors -b "$HOME/.dir_colors")"

For a C shell, generate the equivalent form with dircolors -c and adapt it for the relevant startup file:

$ dircolors -c "$HOME/.dir_colors"
setenv LS_COLORS 'no=0:di=01;34:*.log=01;31:di=01;36:'

Reopen a shell or source the file, then check:

$ . "$HOME/.bashrc"
$ printf 'LS_COLORS is %s\n' "${LS_COLORS:+set}"
LS_COLORS is set

5. Extend the rules without surprising yourself

Use a leading asterisk for a suffix rule such as *.log. The older form .log is accepted but described as obsolete.

Type rules include DIR, FILE, LINK, FIFO, SOCK, EXEC, ORPHAN and MISSING. Two fall back when absent:

• No ORPHAN: ls uses the link colour.
• No MISSING: ls uses the regular-file colour.

Colour values are usually ANSI numbers separated by semicolons. For example, 0 resets the display, 1 makes text brighter, 31 selects a red foreground and 44 selects a blue background. Terminals do not all render every attribute the same way. If a terminal stays coloured after a listing, set both NORMAL and FILE to a reset or a suitable normal foreground sequence.

Spaces, control characters, backslashes, carets and a leading hash in a value or extension need escaping. The format accepts C-style escapes: \e for Escape, \n for newline, \_ for space and \# for a literal hash. Keep unusual control characters out of a shared configuration unless you have tested the terminal that will show them.

6. Diagnose a rule that does not apply

First print the generated fragment and check the environment:

$ printf 'TERM=%s\n' "$TERM"
$ dircolors -b "$HOME/.dir_colors"
LS_COLORS='...';
export LS_COLORS

• Terminal rule missing? Its TERM pattern did not match the current TERM.
• Global rule ignored? The global section ends at the first TERM. Move the rule above that line if it should apply everywhere.
• Assignment looks right, no colour? Check that you are using automatic colour mode, or an alias that enables colour. LS_COLORS supplies the mapping. It does not by itself force ls to emit colour.
• Rule does nothing? Test a filename that actually matches it. A rule for *.log does not match server.LOG, and this format does not supply case handling.

Keep the temporary test directory until the listing behaves as expected. Then remove it with rm -rf /tmp/dir-colour-check, and only when you are certain it holds nothing useful.