Naive bash script to compute how old a project repository is

duration.sh

#!/bin/bash

START_DATE=$(git --no-pager log $(git rev-list --max-parents=0 HEAD) --format="%at")
END_DATE=$(git --no-pager log -n 1 $(git rev-list HEAD^..HEAD) --format="%at")

DURATION=$(( $(($END_DATE - $START_DATE)) / 86400 ))

pluralize() {
    echo $1s
}

make_time_text() {
    if [[ $2 -eq 1 ]]; then
        echo $2 $1
    fi

    if [[ $2 -gt 1 ]]; then
        echo $2 $(pluralize $1)
    fi 
}

concat() {
    echo $1 "$2"
}


if [[ $DURATION > 365 ]]; then
    YEARS=$(( $DURATION / 365 ))
    
    RESULT_TEXT=$(concat "" "$(make_time_text 'year' $YEARS)")

    REMAINING_DAYS=$(( $DURATION % 365 ))

    MONTHS=$(( $REMAINING_DAYS / (7 * 4) ))

    RESULT_TEXT=$(concat "$RESULT_TEXT" "$(make_time_text 'month' $MONTHS)")

    REMAINING_DAYS=$(( $REMAINING_DAYS % (7 * 4) ))
    
    WEEKS=$(( $REMAINING_DAYS / 7 ))

    RESULT_TEXT=$(concat "$RESULT_TEXT" "$(make_time_text 'week' $WEEKS)")

    REMAINING_DAYS=$(( $REMAINING_DAYS % 7 ))

    RESULT_TEXT=$(concat "$RESULT_TEXT" "$(make_time_text 'day' $REMAINING_DAYS)")

fi

echo $RESULT_TEXT