Shell Programming and Scripting

#!/bin/bash

file=$1     # The input log file
maxTime=$2  # The time discrepancy to look for
n=$3        # The number of log entries to memorize
outFile=$4  # The output file

declare -a array

if [[ ! -n $1 || ! -n $2 || ! -n $3 || ! -n $4 ]]; then
    echo "ERROR"
    exit 128
fi

# This value is to print lines AFTER match
till=0

# This is a temp value to compare timestamps
previous=0

# egrep gets rid of all non-timestamped lines
egrep -n '^[0-9]' $file | \
while IFS="[.|:]" read number datetime min sec milli rest; do
    milliseconds=$(date -d "$datetime:$min:$sec" +%s)$milli
    line="$number:$datetime:$min:$sec.$milli|$rest"

    # Memorize the last n lines
    array=("${array[@]}" $line)
    if [[ ${#array[@]} -gt $n ]] ; then
        # get rid of overflow
        array=(${array[@]:1})
    fi

    # Calculate time difference on current and last line
    if [[ $previous -ne 0 ]] ; then
        (( difference = milliseconds - previous ))
    else
        difference=0
    fi

    if [[ $till -gt $number ]] ; then
        echo $line
    else
        if [[ $difference -gt $maxTime ]] ; then
            (( till = number + n ))

            # Print the history
            for item in ${array[@]}
            do
                echo $item
            done

            # Print the current match
            echo $line
        fi
    fi
    previous=$milliseconds
done