change environment variable via script

[der.hans]

Am 23. Dec, 2005 schwätzte Alex Dean so:

> I'm using bash (on OSX).  In ~/.bash_profile, I have a CVSROOT variable set 
> so I can connect to 1 CVS server.  I occasionally want to connect to another 
> cvs server, so I wrote a shell script to set a new CVSROOT value for me.  The 
> script appears to set the value correctly, but it doesn't change my 
> environment settings outside of the script.  It seems like it's a global vs. 
> local variable issue. (CVSROOT is set differently within the context of the 
> script, but is the change is forgotten when the script exits.)  I don't do 
> shell scripts very often, so I'm probably missing something really obvious. 
> How do I tell the script I want to change the value 'for real'?

Running a script or program execs a new shell from which to run the
program. That way the program can't break your current shell.

In order to have a script change environmental variables in the current
shell you need to source the script.

. ./myscript.sh

or

source ./myscript.sh

The former should work with all bourne shell implementations. The latter
works with bash and I think ksh.

For your particular problem you might also just use a command line switch
for cvs or an inline environmental variable assignment.

CVSROOT=":ext:alex at cvs.two.net:/var/lib/cvs" cvs ...

cvs -d :ext:alex at cvs.two.net:/var/lib/cvs ...

Double-check the syntax for cvs as the usage of that switch might not be
correct.

For bonus points figure out how to add an alias for cvstwo that will call
one of the those options to your profile :).

For extra bonus points figure out how to get that alias to use the
bash_completions function for cvs ;-).

ciao,

der.hans

> This is the script :
> #!/bin/sh
> echo "Selected server : "$1;
>
> case "$1" in
>  one)
>    CVSROOT=":ext:alex at cvs.one.net:/var/lib/cvs"; export CVSROOT;
>  ;;
>  two)
>    CVSROOT=":ext:alex at cvs.two.net:/var/lib/cvs"; export CVSROOT;
>  ;;
>  *)
>    echo '???';
>    exit 0;
> esac
>
> echo "CVSROOT value at end of script : "$CVSROOT;
> exit 0;
>
> And here's a session which -should- switch from server 'one' to server 'two', 
> but it doesn't...
>
> sod:~/scripts alex$ echo $CVSROOT
> :ext:alex at cvs.one.net:/var/lib/cvs
> sod:~/scripts alex$ ./cvsswitch two
> Selected server : 'two'
> CVSROOT value at end of script : ':ext:alex at cvs.two.net:/var/lib/cvs'
> sod:~/scripts alex$ echo $CVSROOT
> :ext:alex at cvs.one.net:/var/lib/cvs
> sod:~/scripts alex$
>
> You can see the script set the variable correctly, but the change didn't 
> apply outside of the script.  Why doesn't this work?!
>
> thanks,
> alex
> .
>
>
>
>

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