How to alter PATH within a shell script?

Question

I have several projects that require me to change versions of Java/Grails/Maven. I'm trying to handle this with some scripts that would make the changes. For example:

#!/bin/sh

export JAVA_HOME=/cygdrive/c/dev/Java/jdk1.5.0_22
export PATH=$JAVA_HOME/bin:$PATH
export GRAILS_HOME=/cygdrive/c/dev/grails-1.0.3
export PATH=$GRAILS_HOME/bin:$PATH
export MAVEN_HOME=/cygdrive/c/dev/apache-maven-2.0.11
export PATH=$MAVEN_HOME/bin:$PATH
which java
which grails
which mvn

When this executes, it successfully changes the PATH within the context of the script, but then the script ends, and no change has been accomplished.

How can I run a script in a way to change the PATH in for the shell in which I am currently working?

I'm using Cygwin.

Answer 1

You have to use source or eval or to spawn a new shell.

When you run a shell script a new child shell is spawned. This child shell will execute the script commands. The father shell environment will remain untouched by anything happens in the child shell.

There are a lot of different techniques to manage this situation:

1. Prepare a file sourcefile containg a list of commands to source in the current shell:

   export JAVA_HOME=/cygdrive/c/dev/Java/jdk1.5.0_22
   export PATH=$JAVA_HOME/bin:$PATH
   

   and then source it

   source sourcefile
   

   note that there is no need for a sha-bang at the begin of the sourcefile, but it will work with it.

2. Prepare a script evalfile.sh that prints the command to set the environment:

   #!/bin/sh
   echo "export JAVA_HOME=/cygdrive/c/dev/Java/jdk1.5.0_22"
   echo "export PATH=$JAVA_HOME/bin:$PATH"
   

   and then evaluate it:

   eval `evalfile.sh`
   

3. Configure and run a new shell:

   #!/bin/sh
   export JAVA_HOME=/cygdrive/c/dev/Java/jdk1.5.0_22
   export PATH=$JAVA_HOME/bin:$PATH
   
   exec /bin/bash
   

   note that when you type exit in this shell, you will return to the father one.

4. Put an alias in your ~/.bashrc:

   alias prepare_environ='export JAVA_HOME=/cygdrive/c/dev/Java/jdk1.5.0_22; export PATH=$JAVA_HOME/bin:$PATH;'
   

   and call it when needed:

   prepare_environ
   

Answer 2

You could do that by using the source builtin:

. script_name

Some shells provide an alias named source:

source script_name