How can I execute and export in a single shellscript

Question

I have two shell scripts.

$ cat java_alternative_7
#!/bin/sh
sudo update-java-alternatives -s java-7-oracle

$ cat java_home_7
#!/bin/sh
export JAVA_HOME=/usr/lib/jvm/java-7-oracle

It's simple that I can execute/source these two files.

$ sh java_alternative_7
$ javac -version
javac 1.7.x_yy

$ source java_home_7
$ echo $JAVA_HOME
/usr/lib/jvm/java-7-oracle

How can I do these two steps in a single shot?

Answer 1

If you don't want to merge the scripts, as in

#!/bin/sh

sudo \
    env JAVA_HOME=/usr/lib/jvm/java-7-oracle \
    update-java-alternatives -s java-7-oracle

you may use

#!/bin/sh

sudo \
    env BASH_ENV=path/to/java_home_7 \
    bash -c 'update-java-alternatives -s java-7-oracle'

This would cause the script to run update-java-alternatives in a bash -c in-line script started from env with sudo. The env utility sets the BASH_ENV environment variable to the pathname of the script that sets the JAVA_HOME environment variable. This causes the bash -c script to automatically source the other script before it calls the update-java-alternatives utility.

The use of env to set the environment variables makes sure that the variables are set even though sudo may initially clear the environment.

Answer 2

I'm not sure I'm aware of what I'm doing. Any comments or suggestions will be appreciated.

$ cat java7
#!/bin/sh
alternative=java-7-oracle
sudo update-java-alternatives -s $alternative
export JAVA_HOME=/usr/lib/jvm/$alternative

$ cat java8
#!/bin/sh
alternative=java-8-oracle
sudo update-java-alternatives -s $alternative
export JAVA_HOME=/usr/lib/jvm/$alternative

$ . java7;javac -version;echo $JAVA_HOME
javac 1.7.x_yy
/usr/lib/jvm/java-7-oracle

$ . java8;javac -version;echo $JAVA_HOME
javac 1.8.x_yy
/usr/lib/jvm/java-8-oracle

UPDATE

I'm updating for myself and anyone who needs.

First I added following line to my ~/.bashrc.

#http://serverfault.com/a/276221/113357
export JAVA_HOME=$(readlink -f /usr/bin/java | sed "s:bin/java::")

And my new ~/bin/java_home scripts.

#!/bin/bash
if [ $# -ne 1 ]
then
    echo please select a jname.
    update-java-alternatives -l
    return;
fi
jname=$1
sudo update-java-alternatives -s $jname
source ~/.bashrc

And when I want to change the JDK, I do.

$ source java_home java-7-oracle
$ source java_home java-8-oracle

The JAVA_HOME variable changes even in any new terminals. Previous java7 and java8 changed like this.

$ echo java7
#!/bin/sh
source java_home java-7-oracle

$ echo java8
#!/bin/sh
source java_home java-8-oracle

$