cut a mp3 file by ffmpeg

cutmp3.sh

#!/bin/bash
##############################
# cut a mp3 file
# @author rzeng
# @date 2017-02-12
# @requirements ffmpeg
##############################

if ! [ "$(which ffmpeg)" ];then
    echo "Install ffmpeg first!"
    exit 127
fi

time=$1
input_file=$2
output_file=$3

if [ -z "$time" ];then
    echo 'Give me time!'
    exit 127
fi

if ! [ -f "$input_file" ];then
    echo 'Give me a input file please!'
    exit 127
fi

if ! [ -f "$output_file" ];then
    output_file=${input_file}.cut.mp3
fi

ffmpeg -i $input_file -t $time -acodec copy $output_file