Logging Functions

Overview

Reusable logging functions for Bash scripts with support for log levels and formatted output.

Code

Log Message Prefixes

#!/bin/sh
set -e
 
# prints the script name
log_prefix() {
  echo "$0"
}
 
# prints script name and line number
log_prefix_line() {
  echo "$0:$1"
}
 
# prints script name, line number, and function name
log_prefix_line_func() {
  echo "$0:$1:$2"
}
 
# prints timestamp, script name, line number, and function name
log_prefix_line_func_date() {
  echo "$(date +'%Y-%m-%d %H:%M:%S') $0:$1:$2"
}

Priority-Based Logging

#!/bin/sh
set -e
 
# default priority is 6 (INFO)
DEFAULT_PRIORITY=6
 
log_set_priority() {
  DEFAULT_PRIORITY="$1"
}
 
log_priority() {
  if test -z "$1"; then
    echo "$DEFAULT_PRIORITY"
    return
  fi
  [ "$1" -le "$DEFAULT_PRIORITY" ]
}
 
log_tag() {
  case "$1" in
    0) echo "EMERG" ;;
    1) echo "ALERT" ;;
    2) echo "CRIT" ;;
    3) echo "ERR" ;;
    4) echo "WARNING" ;;
    5) echo "NOTICE" ;;
    6) echo "INFO" ;;
    7) echo "DEBUG" ;;
    *) echo "UNKNOWN" ;;
  esac
}
 
echoerr() {
  echo "$@" >&2
}
 
log_debug() {
  log_priority 7 || return 0
  echoerr "$(log_prefix)" "$(log_tag 7)" "$@"
}
 
log_info() {
  log_priority 6 || return 0
  echoerr "$(log_prefix)" "$(log_tag 6)" "$@"
}
 
log_err() {
  log_priority 3 || return 0
  echoerr "$(log_prefix)" "$(log_tag 3)" "$@"
}
 
log_crit() {
  log_priority 2 || return 0
  echoerr "$(log_prefix)" "$(log_tag 2)" "$@"
}

Usage Example

#!/bin/sh
. ./logging.sh
 
# set log level to DEBUG (7) to see all messages
log_set_priority 7
 
log_debug "Starting script..."
log_info "Processing files..."
log_err "Something went wrong!"
log_crit "Critical failure!"

Details

Log Levels (Syslog Standard)

Level	Tag	Description
0	EMERG	System is unusable
1	ALERT	Action must be taken
2	CRIT	Critical conditions
3	ERR	Error conditions
4	WARNING	Warning conditions
5	NOTICE	Normal but significant
6	INFO	Informational messages
7	DEBUG	Debug-level messages

Messages are only printed if their priority level is less than or equal to the configured DEFAULT_PRIORITY.

Appendix

Note created on 2025-12-23 and last modified on 2025-12-23.

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Bash - Logging Functions