How to alter PATH within a shell script?

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
   

You could do that by using the source builtin:

. script_name

Some shells provide an alias named source:

source script_name