A tool for testing the performance of 2 methods of appending strings in bash. Created for https://stackoverflow.com/a/47878161/117471

append_test.sh

#!/bin/bash -e

output(){
        ptime=$ctime;
        ctime=$(date +%s.%N);
        delta=$(bc <<<"$ctime - $ptime");
        printf "%2s. %16s chars  time: %s  delta: %s\n" $n "$(bc <<<"10*(2^$n)")" $ctime $delta;
}

method1(){
        echo 'Method: a="$a$a"'
        for n in {1..32}; do a="$a$a"; output; done
}

method2(){
        echo 'Method: a+="$a"'
        for n in {1..32}; do a+="$a";  output; done
}

ctime=0; a="0123456789"; time method$1