Debian and Ubuntu changed the default shell /bin/sh from bash (Bourne Again Shell) to dash (Debian Almquist Shell).

The advantage of dash is its size, speed and POSIX compliance. The disadvantage is that many scripts written for bash won't work anymore because bash has specific features - so called "bashisms".

 

One of this bashisms, I used frequently in the xxsvideo build system is the " indirect variable expansion". Which makes it possible to execute the following script:

#!/bin/bash                                                                                                                                        
                                                                                                                                                   
CONFIG_BUSYBOX=y

PACKAGENAME="BUSYBOX"
PACKAGECONFIG=CONFIG\_$PACKAGENAME

if [ "${!PACKAGECONFIG}" = "y" ]; then
        echo $PACKAGENAME "is selected"
else
        echo $PACKAGENAME "is NOT selected"
fi

If you call this script with bash you receive as expected "BUSYBOX is selected".

With dash you see:

./test.sh: 13: Bad substitution

I was looking a long time for the right way to replace this {!VAR} statement. But it's quite simple and suddenly I found a thread describing it:

#!/bin/dash

CONFIG_BUSYBOX=y

PACKAGENAME="BUSYBOX"

PACKAGECONFIG=CONFIG\_$PACKAGENAME

if [ "$(eval echo '$'$PACKAGECONFIG)" = "y" ]; then

    echo $PACKAGENAME "is selected"

else

    echo $PACKAGENAME "is NOT selected"

fi

 

In short: With dash you write:

eval echo '$'$VARIABLE

which is equivalent to bash

echo ${!VARIABLE}

 

... I think ;-)