bestcompression

#!/bin/bash

# bestcompression - 
# -a , when present skips files already compressed

Z="compress"	gz="gzip"	bz="bzip2"
Zout="/tmp/bestcompression.$$.Z"
gzout="/tmp/bestcompression.$$.gz"
bzout="/tmp/bestcompression.$$.bz2"
skipcompression=1

if [ "$1" = "-a" ]
then
	skipcompression=0
	shift
fi

if [ $# -eq 0 ]
then
	echo "ERROR, $(basename $0), [-a] files to be compressed." >&2
	exit 1
fi

trap "/bin/rm -f $Zout $gzout $bzout" EXIT

for name in "$@"
do
	if [ ! -f "$name" ]
	then
		echo "WARNING, '$name' file not found, skipping" >&2
		continue
	fi

	if [ "$(echo $name | egrep '(\.Z$|\.gz$|\.bz2$)')" != "" ]
	then
		if [ $skipcompression -eq 1 ]
		then
			echo "Skipping file '$name' as it is already compressed" >&2
			continue
		else
			echo "WARNING, compressing file already compressed" >&2
		fi
	fi

	# Compress the 3 files in paralell
	$Z < $name > $Zout &
	$gz < $name > $gzout &
	$bz < $name > $bzout &

	wait # Wait for all files to be compressed

	smallest="$(ls -l "$name" $Zout $gzout $bzout | awk '{print $5"="NR}' | sort -n | cut -d= -f2 | head -1 )"

	case "$smallest" in
		1 )	echo "No space savings by compressing '$name'. Left as is."
				;;
		2 )	echo "Best compression is with compress. File renamed ${name}.Z"
				mv $Zout "${name}.Z"; rm -f "$name"
				;;
		3 )	echo "Best compression is with gzip. File renamed ${name}.gz"
				mv $gzout "${name}.gz"; rm -f "$name"
				;;
		4 )	echo "Best compression is with bzip2. File renamed ${name}.bz2"
				mv $bzout "${name}.gz"; rm -f "$name"
				;;
	esac
done

exit 0