SixLogger

A Simple POSIX-compliant Logger function for shell scripts.

Requirements

Has only a few requirements:

• basename
• date
• tr

Globals

SIXLOGGER_DEBUG and SIXLOGGER_NO_COLOR take precedence over DEBUG and NO_COLOR.

Name	Description	Type	Default
SIXLOGGER_DEBUG or DEBUG	If set to true or 1, show debug messages	boolean	false
SIXLOGGER_NO_COLOR or NO_COLOR	If set to true or 1, disable colored terminal output	boolean	false
SIXLOGGER_COLOR_DEBUG	Set output color for debug messages	ANSI escape sequence	\033[0;34m
SIXLOGGER_COLOR_INFO	Set output color for info messages	ANSI escape sequence	\033[0;32m
SIXLOGGER_COLOR_WARN	Set output color for warn messages	ANSI escape sequence	\033[1;33m
SIXLOGGER_COLOR_ERROR	Set output color for error messages	ANSI escape sequence	\033[0;31m
SIXLOGGER_COLOR_FATAL	Set output color for fatal messages	ANSI escape sequence	\033[1;31m
E_SIXLOGGER_UNKNOWN_LOGLEVEL	Set status code for unknown loglevel error	number	30

Arguments

The sixlogger function takes two arguments:

Sh	Name	Description	Type
$1	loglevel	Loglevel for logger (e.g.: info)	string
$*	message	Message to log (e.g.: "My log message")	string

Outputs

Output	Description
stdout	Writes info, warn and debug log messages to stdout.
stderr	Writes error and fatal log messages to stderr.

Returns

Status Code	Description
0	No errors.
30	E_SIXLOGGER_UNKNOWN_LOGLEVEL

Usage

Download script

# Download the sixlogger function into a new script
SIXLOGGER_VERSION=0.1.1
cat <<EOF > sixlogger.sh && chmod +x sixlogger.sh
#!/bin/sh
$(curl -sSfL "https://github.com/esaporski/sixlogger/releases/download/${SIXLOGGER_VERSION}/sixlogger.sh")
EOF

Embedding into a file

# Add the sixlogger function after shebang `#!`
SIXLOGGER_VERSION=0.1.1
curl -sSfL "https://github.com/esaporski/sixlogger/releases/download/${SIXLOGGER_VERSION}/sixlogger.sh" |
  sed -i '/#!/r /dev/stdin' my_script.sh

Source it from another file

After downloading the script with the command above, add these lines in your script:

#!/bin/sh

# Get script directory absolute path
script_dir="$(cd "$(dirname "$0")" >/dev/null 2>&1 && pwd)"

. "${script_dir}/sixlogger.sh"

Examples

• Simple
• Advanced
• Capture command output

SIXLOGGER_DEBUG and SIXLOGGER_NO_COLOR

DEBUG=true
sixlogger debug "A debug message"
# Outputs:
# > \e[0;34m2025-01-01T00:00:00+00:00 | debug | example.sh | A debug message\e[0m

# `SIXLOGGER_DEBUG` takes precedence over `DEBUG`
# so you will not see this message
SIXLOGGER_DEBUG=false
sixlogger debug "You will not see me!"
# Outputs:
# >

# ...but this works
DEBUG=false
SIXLOGGER_DEBUG=true
sixlogger debug "Now you can see me again"
# Outputs:
# > \e[0;34m2025-01-01T00:00:00+00:00 | debug | example.sh | Now you can see me again\e[0m

# It's the same thing for `SIXLOGGER_NO_COLOR` and `NO_COLOR`
NO_COLOR=false
sixlogger info "Colored terminal output is enabled by default"
# Outputs:
# > \e[0;32m2025-01-01T00:00:00+00:00 | info | example.sh | Colored terminal output is enabled by default\e[0m

# Disables colored output even with `NO_COLOR` still set to `false`
SIXLOGGER_NO_COLOR=true
sixlogger info "Colored terminal output is disabled now"
# Outputs:
# > 2025-01-01T00:00:00+00:00 | info | example.sh | Colored terminal output is disabled now

Capturing output and status code from commands

filename="my_file"
sixlogger info "Removing file '${filename}'"

# Initialize the `status_code` variable with `0`
status_code=0

# Let's redirect `stderr` to `stdout` and save the output of the command we want to run
# If the command fails, we save the exit status code into `status_code`
output=$(rm "$filename" 2>&1) || status_code=$?

# Now we check if the exit status code is still `0` (success)
# If not, we print a message and exit passing the failed command's status code
[ "$status_code" -eq 0 ] || {
 sixlogger fatal "Failed to remove '${filename}' with status code '${status_code}': ${output}"
 exit "$status_code"
}
sixlogger info "Deleted '${filename}'"

# On success:
# > 2025-01-01T00:00:00+00:00 | info | example.sh | Removing file 'my_file'
# > 2025-01-01T00:00:00+00:00 | info | example.sh | Deleted 'my_file'

# On failure:
# > 2025-01-01T00:00:00+00:00 | info | example.sh | Removing file 'my_file'
# > 2025-01-01T00:00:00+00:00 | fatal | example.sh | Failed to remove 'my_file' with status code '1': rm: cannot remove 'my_file': No such file or directory
# > echo $?
# > 1

Logging into a file

When logging into a file, you need to remember that:

• error and fatal messages are sent to stderr.
• You need to disable colored output with SIXLOGGER_NO_COLOR or NO_COLOR.

SIXLOGGER_NO_COLOR=true # or NO_COLOR=true
export SIXLOGGER_NO_COLOR

# You can log `stdout` and `stderr` into different files
./my_script.sh 1>/var/log/my_script.log 2>/var/log/my_script.err.log

# Or you can log everything into a single file
./my_script.sh >/var/log/my_script.log 2>&1

If you want to disable colored output when stdout or stderr are being redirected to another file or command, you can include this snippet in your own script:

# Disable color if redirecting `stdout` or `stderr` to another command or file
if ! { [ -t 1 ] && [ -t 2 ]; }; then SIXLOGGER_NO_COLOR=true; fi && export SIXLOGGER_NO_COLOR

# Or...
if ! { [ -t 1 ] && [ -t 2 ]; }; then NO_COLOR=true; fi && export NO_COLOR

Changelog

CHANGELOG.md

License

MIT License