Script that creates self extracting executable script from tar.gz file.

selftar.sh

#!/bin/sh


if [ $# -eq 0 ]; then
        echo "This script creates self extractable executable"
        echo Usage: $0 TAR.GZ [COMMAND]
        exit;
fi
if [ $# -gt 0 ]; then
        TAR_FILE=$1
fi
EXIT_COMMAND=exit
if [ $# -gt 1 ]; then
        EXIT_COMMAND="exec $2"
fi

SELF_EXTRACTABLE="$TAR_FILE.self"

echo '#!/bin/sh' > $SELF_EXTRACTABLE
echo 'dd bs=1 skip=`head -3 $0 | wc -c`  if=$0  | gunzip -c  | tar -x' >> $SELF_EXTRACTABLE
echo "$EXIT_COMMAND" >> $SELF_EXTRACTABLE

cat $TAR_FILE >> $SELF_EXTRACTABLE
chmod a+x $SELF_EXTRACTABLE

change this line:

echo 'dd bs=1 skip=`head -3 $0 | wc -c`  if=$0  | gunzip -c  | tar -x' >> $SELF_EXTRACTABLE

to:

echo 'dd status=none bs=`head -3 $0 | wc -c` skip=1 if=$0  | gunzip -c  | tar -x' >> $SELF_EXTRACTABLE

and it will be 10 times faster :D

Could you explain why this makes it faster?

actually, from my test, this is fine for small files, but when you try to self-extract 2GB file, it get VERY slow..

i did following to make it way faster (almost as fast as normally extracting using tar zxvf )

change

echo 'dd bs=1 skip=`head -3 $0 | wc -c`  if=$0  | gunzip -c  | tar -x' >> $SELF_EXTRACTABLE

TO

echo 'tail -c +$(($(head -3 $0 | wc -c | tr -d " ")+1)) "$0" | tar zxvf -' >> $SELF_EXTRACTABLE

The reason for this is because dd bs=1 is an extremely inefficient way to skip the first few bytes of the file. It reads one byte at a time, causing significant performance overhead.

i also added tr -d " " because this script would not work properly on MacOS (works fine on linux)
The reason, is that wc -c reports "spaces" in its output on Mac.. so we need to clear them with tr command.
now script works on both MacOS and Linux