Bash – setting JAVA_HOME and PATH with update-alternatives

bashjavapathshell-script

EDITED

The question was more about bash script them java environment and thanks for those whom had the patience and spare the time to reply me. I am much obliged.

As for the Java environment I started using sdkman. When I started this little script I was actually looking for something just like that, I was considering doing something similar. Whoever is looking for an answer to my question I recommend using the tool. It doesn't matter if you get yourself your own script, I urge you to git it a try.

The sdkman will care for language version installation, side lunges need (like maven, gradle and kotlin) as well as environment variables.

https://sdkman.io/

Original Question

I'm building a bash script to set both the JAVA_HOME and the PATH of the user automatically considering the version of the active java, however for some reason PATH is not being built correctly, it is adding blanks instead of ": ", could anyone tell me why?

Below the script.

Thanks!

#!/bin/bash

export JAVA_HOME=$(dirname $(dirname `readlink -f /etc/alternatives/java`))

IFS=':';
for i in $PATH;
do
        JAVA1=$i/bin/java
        JAVA2=$i/java
        if [ -d "$i" ];
        then
                if [ ! -L "$JAVA1" ] && [ -x "$JAVA1" ] || [ ! -L "$JAVA2" ] && [ -x "$JAVA2" ];
                then
                        echo "dropping path: $i";
                else
                        NEW=$NEW:$i
                fi
        fi
done
PATH=$NEW:$JAVA_HOME/bin
echo 
echo "Final:"
echo $PATH

Sample output:

$ ./java_home_setter.sh 
dropping path: /usr/lib/jvm/java-8-openjdk-amd64/jre/bin

Final:
 /usr/local/sbin /usr/local/bin /usr/sbin /usr/bin /sbin /bin /usr/games /usr/local/games /snap/bin /usr/lib/jvm/java-8-openjdk-amd64/bin

Best Answer

Thast's because you have altered IFS variable to use ':'

so when its output your variable its replaced with default output field separator which is 'space' thinking that ':' is input field separator .

you have take backup of it before using IFS like below :

OIFS=$IFS
IFS=':';

after 'for' loop is done , restore it :

IFS=$OIFS

Also remove the ':' which starts with no path preceding that 

PATH=${PATH#:*}

Your script should be like :

#!/bin/bash

export JAVA_HOME=$(dirname $(dirname `readlink -f /etc/alternatives/java`))

OIFS=$IFS
IFS=':';
for i in $PATH;
do
        JAVA1=$i/bin/java
        JAVA2=$i/java
        if [ -d "$i" ];
        then
                if [ ! -L "$JAVA1" ] && [ -x "$JAVA1" ] || [ ! -L "$JAVA2" ] && [ -x "$JAVA2" ];
                then
                        echo "dropping path: $i";
                else
                        NEW=$NEW:$i
                fi
        fi
done
IFS=$OIFS
PATH=$NEW:$JAVA_HOME/bin
PATH=${PATH#:*}
echo 
echo "Final:"
echo $PATH
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