Using Colour in Shell Scripts for Logging

Why Use Colour in Shell Scripts?

I find it useful in shell scripts to define a set of logging functions to provide feedback. Adding colour to the log level helps:

Highlight errors, warnings, and successes
Improve script readability
Save time during debugging

Let’s walk through how to implement colour-coded logging in your shell scripts using ANSI escape codes.

ANSI Colour Codes

ANSI escape codes control formatting in terminal output, including colour. Here’s a table of common foreground and background colour codes:

Colours

Colour	Foreground Code	Background Code
Black	30	40
Red	31	41
Green	32	42
Yellow	33	43
Blue	34	44
Magenta	35	45
Cyan	36	46
White	37	47
Bright Black	90	100
Bright Red	91	101
Bright Green	92	102
Bright Yellow	93	103
Bright Blue	94	104
Bright Magenta	95	105
Bright Cyan	96	106
Bright White	97	107

Reset with \033[0m to end colouring.

Defining Helper Functions

A good practice is to define reusable logging functions at the top of your script:

# Colour constants
RESET="\033[0m"
RED="\033[0;31m"
GREEN="\033[0;32m"
YELLOW="\033[0;33m"
BLUE="\033[0;34m"
BG_RED="\033[41m"
BG_YELLOW="\033[43m"

# Logging functions
log_info() {
  echo -e "${BLUE}[INFO]${RESET} $1"
}

log_success() {
  echo -e "${GREEN}[SUCCESS]${RESET} $1"
}

log_warning() {
  echo -e "${YELLOW}[WARNING]${RESET} $1"
}

log_error() {
  echo -e "${RED}${BG_YELLOW}[ERROR]${RESET} $1" >&2
}

Example Usage

log_info "Starting backup process."
if backup_files; then
  log_success "Backup completed successfully."
else
  log_error "Backup failed."
fi

This approach makes logs readable and immediately actionable, especially when scrolling through long outputs.

Tips for Usage

Avoid using colours in scripts that may pipe output to other commands unless optional.
Use colour only if the output is a terminal: if [ -t 1 ]; then ...
Consider allowing a --no-colour flag to disable colours in CI environments.
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Conclusion

Coloured logging can transform your shell scripts from dull to delightful. By centralising your styles into helper functions, your scripts stay clean, readable, and informative. Whether you’re debugging or sharing your work with others, a bit of colour goes a long way.

Happy scripting!