word replacer new

#!/bin/bash

help_message="
Script have 2 modes: interactive and noninteractive.
For interactive mode use args:
-i  insensitive search for replacement
-v  verbose entered args
-I  start interactive mode
Exemple:
scriptname -I [-i]

For noninteractive use args:
-i  insensitive search for replacement
-v  verbose entered args
-d  path to target directory
-t  a word or expression that must be replaced
-r  word or expression to be replaced by
Exemple:
scriptname [-i] -d /path/to/dir -t 'exemple_1' -r 'i love exemples'
or with regexp:
scriptname [-i] -d /path/to/dir -t 'ex..ple_1$' -r 'i love exemples'
"

function main_work(){
    for arg in $script_args; do case $arg in "-i") insensitive_trigger="1";; "-v") dbg="1";; esac; done

    [ "$interactive_trigger" == "1" ] && {
        [[ "$dir_path" || "$old_expression" || "$new_expression" ]] && echo -e "why you use args in interactive mode?\n"

        read -r -p "path to work dir > " dir_path
        IFS= read -r -p "target word      > " old_expression
        IFS= read -r -p "replacement word > " new_expression
    }
    [ ! -d "$dir_path" ] && { echo -e "\nDirectory \"$dir_path\" does not exist\nMake sure that the path exists"; error_exit_trigger="1"; }
    [ -z "$old_expression" ] && { echo -e "\nNot found the target word"; error_exit_trigger="1"; }
    [ -z "$new_expression" ] && { echo -e "\nNot found the word for replacement"; error_exit_trigger="1"; }
    [ "$error_exit_trigger" == "1" ] && exit

    for file in $(find $dir_path -type f); do
        if [ "$insensitive_trigger" == "1" ]; then
            sed -E -i -e "s/$old_expression/$new_expression/ig" $file
        else
            sed -E -i -e "s/$old_expression/$new_expression/g" $file
        fi
    done

    [ "$dbg" == "1" ] && echo -e "\ndir path   : $dir_path\ntarget word: $old_expression\nreplaced by: $new_expression\ninsensitive: $insensitive_trigger\n"

    echo -e "Done\nHave a nice day"
    exit
}
function error_handler(){
    error_value="$OPTARG"
    [ "$error_value" == "d" ] && {
        echo -e "Err: -d must contain folder path argument"
        error_exit_trigger="1"
    }
    [ "$error_value" == "t" ] && {
        echo -e "Err: -t must contain target word or expression"
        error_exit_trigger="1"
    }
    [ "$error_value" == "r" ] && {
        echo -e "Err: -r must contain target word or expression for replacement"
        error_exit_trigger="1"
    }
    [ "$error_exit_trigger" == "1" ] && {
        echo "For help use -h"
        exit
    }
}

script_args="$@"
insensitive_trigger="0"
error_exit_trigger="0"
dbg="0"

for arg in $script_args;do
    case $arg in
        "-h"|"--help") echo "$help_message" && exit ;;
        "-I") interactive_trigger="1"; main_work;   ;;
    esac
done

while getopts ":d:t:r:" arg;do
    case $arg in
        "d") dir_path="$OPTARG"       ;;
        "t") old_expression="$OPTARG" ;;
        "r") new_expression="$OPTARG" ;;
        :)   error_handler            ;;
    esac
done

main_work