A simple timer / stopwatch implemented as a bash function.

timer.sh

#!/bin/bash

# Display the duration between timer start and stop.
#
# Usage:  timer {start|stop} [format]
#
# Example:
#
#   timer start
#   <script_commands>
#   timer stop [format]


timer() {
    local cmd="$1"
    local timer_format
    
    if [[ -n "$2" ]]; then
        timer_format="$2"
    else
        timer_format='%-Hh%-Mm%-Ss'
    fi
    
    case $cmd in
        start)
            # This can't be local because we need it to persist across calls.
            _timer_StartSecs=$(date +'%s')
            ;;
        stop)
            if [[ ! $_timer_StartSecs ]]; then
                echo "$FUNCNAME did not record a start." >&2
                return 1
            fi
            
            local _timer_StopSecs=$(date +'%s')
            local DiffSecs=$(($_timer_StopSecs-$_timer_StartSecs))
            local TimeLapse=$(date -u -d@"$DiffSecs" +"$timer_format")
            
            echo "$TimeLapse"
            ;;
        *)
            echo "$FUNCNAME: Invalid command '$cmd'." >&2
            return 1
            ;;
    esac
}