Local MySQL database backup

#!/bin/bash

# Script for backing up local MySQL database
# It's good to use it with Cron tasks
# Author: Michal ŠMAHEL (ceskyDJ) <ceskyDJ@seznam.cz>
# Copyright: (C) Michal ŠMAHEL (ceskyDJ) 2018

# Control vars defaults definition
force=false;
remove=false;
time=false;
user="root";
password="";
validity="31";

# Load config from arguments
i=0; # Iteration
skip=false; # Sign for skip next argument (because of value)

for arg in $@;
do
    if [ $skip == true ]; then
        skip=false;
        i=$(echo "$i + 1"|bc);
        continue;
    fi

    case $arg in
    # Display help
    "-h" | "--help")
        echo "Usage: $0 DIRECTORY [OPTIONS...]";

        echo -e "\nCommand structure:";
        echo -e "  DIRECTORY\t\t\tdirectory for saving backups";
        echo -e "  OPTIONS\t\t\tadditional arguments";

        echo -e "\nAvailable arguments:";
        echo -e "  -f, --force\t\t\tforce rewrite backup file";
        echo -e "  -r, --remove\t\t\tremove old backup files (after month)";
        echo -e "  -t, --time\t\t\tadd time to backup file names";
        echo -e "  -u USER, --user=USER\t\tset database user (with full read permissions) - default: 'root'";
        echo -e "  -p PASS, --password=PASS\tset password for database user - default: ''";
        echo -e "  -v DAYS, --validity=DAYS\tset backup file validity in days (useful only with remove argument) - default: '31'";
        echo -e "  -h, --help\t\t\tdisplay this help";

        exit;
        ;;
    # Allow backup rewriting
    "-f" | "--force")
        force=true;
        ;;
    # Allow old backup files removing
    "-r" | "--remove")
        remove=true;
        ;;
    # Adding time
    "-t" | "--time")
        time=true;
        ;;
    # User change
    "-u")
        user=${@:$i+2:1}; # +1 (it starts from 1), +1 (move to next iteration index)
        skip=true;
        ;;
    --user=*)
        user=$(echo $arg | cut -b 8-);
        ;;
    # Password change
    "-p")
        password=${@:$i+2:1}; # +1 (it starts from 1), +1 (move to next iteration index)
        skip=true;
        ;;
    --password=*)
        password=$(echo $arg | cut -b 12-);
        ;;
    # Backup validity change
    "-v")
        validity=${@:$i+2:1}; # +1 (it starts from 1), +1 (move to next iteration index)
        skip=true;
        ;;
    --validity=*)
        validity=$(echo $arg | cut -b 12-);
        ;;
    # Bad argument
    *)
        # First argument + valid directory
        if [ $i == 0 ] && [ -d $arg ]; then
            dir=$arg;
        # First argument + not existing directory
        elif [ $i == 0 ] && [ ! -d $arg ]; then
            echo "Directory you specified is wrong. Enter valid directory or use -h or --help argument for display help.";

            exit;
        # Second and next argument
        else
            # Invalid argument
            echo "You entered bad argument '$arg'. Try -h or --help argument to display help.";

            exit;
        fi
        ;;
    esac

    i=$(echo "$i + 1"|bc);
done

# Directory verification
if [ ! $dir ]; then
    echo "Directory you specified is wrong. Enter valid directory or use -h or --help argument for display help.";

    exit;
fi

# Date and time format setting
if [ $time == true ]; then
    format="%Y-%m-%d_%T";
else
    format="%Y-%m-%d";
fi

# Backup creation
backupFile="$dir/database_`date +$format`.sql.gz";

# Only if backup wasn't created (or rewrite is allowed)
if [ $force == true ] || [ ! -f $backupFile ]; then
    mysqldump -u $user --password=$password --all-databases | gzip > $backupFile
fi

# Old backups removing
if [ $remove == true ]; then
    for file in $dir/*.sql.gz; do
        length=$(expr length $dir); # -> length of directory string

        start=$(echo "11 + $length"|bc); # -> start index
        end=$(echo "20 + $length"|bc); # -> end index
        dateString=$(echo $file | cut -b $start-$end); # -> YYYY-MM-DD

        dateFormat=$(date -d $dateString +"%Y%m%d"); # -> YYYYMMDD

        minimum=$(date -d -$validity+"day" +"%Y%m%d");

        if [ $minimum -ge $dateFormat ]; then
            rm $file;
        fi
    done
fi