ampm-to-24

#! /usr/bin/bash

## This script replaces time entries in am/pm format to 24hs
##   $ echo "The event starts at 03:25pm and 11:11AM" | ./ampm-to-24
##   The event starts at 15:25 and 11:11

# Match time entries: 03:25pm 11:11AM
regex='(0[0-9]|1[0-2]):([0-5][0-9])(AM|PM|am|pm)'

# Read STDIN line by line
while read line; do
    # Search of all the occurences of the reges
    while [[ $line =~ $regex ]]; do
        hour=${BASH_REMATCH[1]}
        min=${BASH_REMATCH[2]}
        ampm=${BASH_REMATCH[3]}
        # If its pm, sum 12
        if [[ "${ampm^^}" = "PM" ]]; then
            if [[ "$hour" != "12" ]]; then
                hour=$(expr $hour + 12)
            fi
        elif [[ "$hour" = "12" ]]; then
            hour="00"
        fi

        # Replace the hour
        line=${line/"${BASH_REMATCH[0]}"/"$hour:$min"}
    done

    # Print line
    echo $line
done