Question

I have this script below that will be daemonized and triggered possibly hundreds if not thousands of times by different users.

The script uses inotifywait to watch a folder for an upload and then move the uploaded file to its final destination for presentation, after rotating (backup/move) previous uploads. The code will be run against different upload folders that are created on the fly.

#!/bin/bash

db="$VAR1"/path/to/upload/folder/
s3="$VAR2"/path/to/remote/folder

inotifywait -m -r -e attrib "$db" |
while read dir ev file;
do

        for dirnum in $(cd "$s3"; ls */*.png | sed 's%/.*%%' | sort -nr)
        do
                 next=$(($dirnum + 1));                       
                 mv "$s3/$dirnum/post$dirnum.png" "$s3/$next/post$next.png";
        done

        mv "$db"/"$file"  "$s3"/1/post1.png

done

What can I do to optimize it? Or should it be rewritten a faster programming language? Also, how can I test scripts under a certain amount of load?

Answer 1

This does not give identical behavior, but it avoids sorting:

#!/bin/bash

db="$VAR1"/path/to/upload/folder/
s3="$VAR2"/path/to/remote/folder

inotifywait -m -r -e attrib "$db" |
while read dir ev file;
do
    dirnum=1
    while test -e "$s3/$dirnum"; do : $(( dirnum += 1 )); done
    while test $dirnum -gt 0; do
        next=$(( dirnum + 1 ));    
        mkdir -p $s3/$next                   
        mv "$s3/$dirnum/post$dirnum.png" "$s3/$next/post$next.png"
        : $(( dirnum -= 1 ))
    done
    mv "$db/$file" "$s3"/1/post1.png
done

If you keep track of the highest number stored to $s3, you can avoid the first
loop. Doing so is slightly more fragile if other processes are creating files
in $s3, but in that case you have a race condition even in this simplistic solution.
It would be a lot simpler to not rename the files, but put the first file uploaded in
$s3/1, and the next in $s3/2. In that case the script can be written:

#!/bin/bash

db="$VAR1"/path/to/upload/folder/
s3="$VAR2"/path/to/remote/folder
dirnum=1
while test -e "$s3/$dirnum"; do : $(( dirnum += 1 )); done
inotifywait -m -r -e attrib "$db" |
while read dir ev file;
do
    mkdir -p "$s3"/$dirnum
    mv "$db/$file" "$s3"/$dirnum/post$dirnum.png
    : $(( dirnum += 1 ))
done