Re: Script to conditionally find and compress files recursively

On Tue, 11 Jun 2024 14:53:27 +0800, J Newman wrote:

Hi, I'm interested in writing a script that will:
 
1. Find and compress files recursively
2. After the first 5 seconds of compressing, if the compression ratio >1
(i.e. the compressed file will be larger than the uncompressed file), it
tries another compression algorithm.
3. If the other compression algorithm still has a ratio >1, it tries
another algorithm, until a list is exhausted.
4. If the list is exhausted, it skips compressing that file.
 
Any suggestions on how to proceed?

You could use dd to extract a representative chunk of the file to
compress and compare size.

uncompressedsize=$(dd status=none if="$file" bs=1M count=1|wc -c)
compressedsize=$(dd status=none if="$file" bs=1M count=1|$compresscmd|wc -c)

You could get fancy and try all the compression commands you have
and pick the one with smallest output for the actual compression.
That's all assuming the beginning of the file is representative of
the content throughout. If it's not, no way to tell without compressing
the whole thing.