How to check if currently running shell is BusyBox

Question

I tried different variants

echo $0
echo $shell
echo $SHELL
ps -p $$

but none of them can give a distinctive output. I can do something like this but it's ugly and hackish:

if ls --help 2>&1 | grep BusyBox; then
    echo "it is BusyBox"
else
    echo "it is NOT BusyBox"
fi

Answer 1

Another way requiring Linux and readlink :

#!/bin/ash
exe=`exec 2>/dev/null; readlink "/proc/$$/exe"`
case "$exe" in
*/busybox)
    echo "It's a busybox shell."
    ;;
esac

Answer 2

Personally I favour:

if ps ax -o pid,comm | grep `echo $$` | grep busybox ; then
    echo "it is BusyBox"
fi

Which is a fair check to ensure you are running busybox shell.

This works by having ps generate a list of pids vs program names then finding our pid and checking if the program name contains busybox.

Answer 3

Might not be perfect but this is how I check:

test -h /bin/ls # busybox or other single binary system
test -h /bin/ls && test `readlink /bin/ls` = busybox # it is busybox