Syntax error in expression for if statement in bash

Question

The codes are below, I want to check some files whose file size is less than 410Bytes:

for file in *; do
    if [[ "$file" =~ ^dataset([0-9]+)$ && `du -b $file/${BASH_REMATCH[1]}_conserv.png` -lt 410 ]]; then
    cd $file
    $some_commands
    cd ..
    fi
done

However, when I run this script, it complains like this:

less_than_410.bash: line 2: [[: 13605   dataset4866/4866_conserv.png: syntax error in expression (error token is "dataset4866/4866_conserv.png")

Does anyone have ideas about how to fix this? Thanks!

Answer 1

du -b file

It will print file size and name. Use cut to get size only:

du -b file | cut -f 1

Answer 2

Rather than using such a complex expression, just do:

find . -maxdepth 1 -regex '.*/dataset[0-9]+' -size -410c

(Note that -maxdepth and -regex are both gnu extensions to find. Since your question is tagged linux, those options are probably available.)

Answer 3

Use bash extended globbing to restrict the file loop:

shopt -s extglob
for file in dataset+([0-9]); do
    num=${file#dataset}
    (( $(stat -c %s "$file/${num}_conserv.png") >= 410 )) && continue
    do stuff here
done