[Nottingham] Bash Variables

[Mike Haber]

Hi, 

 
> With newshell=Y a new shell is created for each script run.  
> Each child-script inherits the environment from its parent 
> shell and while the child is able to modify its environment 
> (export X=Y) these changes do not propagate back the parent 
> environment and the parent will still have access to the 
> "previous value".  This is why 'cd' has to be a shell built - 
> it would not be able to modify PWD in your current shell if 
> it were a normal executable.
> 
> With newshell=N everything is executed in the same shell so 
> there are no previous values to retrieve - only what you 
> changed it to with the most recent export. 

Thanks for the explanation Duncan, and also Dan for his reply.
I think I the answer to the particualar problem is that we can't get at any previous values.

Cheers
Mike

> 
> HTH 
> 
> Have fun,
> Duncan
> 
> #!/bin/bash
> # Usage: ./test1.sh Y|N
> 
> # Run children in new shells or not.
> newshell=$1
> [ "X$newshell" != "XY" -a "X$newshell" != "XN" ] && newshell=Y
> 
> v=$2
> [ "X$v" == "X" ] && v=1
> 
> # change an environment variable
> export FOO=$v
> echo Pre: v=$v , FOO=$FOO
> if [ $FOO -lt 5 ]; then
> 	let w=v+1
> 	if [ "$newshell" == "Y" ]; then 
> 		./test1.sh $newshell $w
> 	elif [ "$newshell" == "N" ]; then
> 		. test1.sh $newshell $w
> 	fi
> else
> 	echo "Finished"
> fi
> echo Post: v=$v , FOO=$FOO
> ### END OF SCRIPT
> 
> # Giving:
> ./test1.sh Y
> Pre: v=1 , FOO=1
> Pre: v=2 , FOO=2
> Pre: v=3 , FOO=3
> Pre: v=4 , FOO=4
> Pre: v=5 , FOO=5
> Finished
> Post: v=5 , FOO=5
> Post: v=4 , FOO=4
> Post: v=3 , FOO=3
> Post: v=2 , FOO=2
> Post: v=1 , FOO=1
> 
> ./test1.sh N
> Pre: v=1 , FOO=1
> Pre: v=2 , FOO=2
> Pre: v=3 , FOO=3
> Pre: v=4 , FOO=4
> Pre: v=5 , FOO=5
> Finished
> Post: v=5 , FOO=5
> Post: v=5 , FOO=5
> Post: v=5 , FOO=5
> Post: v=5 , FOO=5
> Post: v=5 , FOO=5
> 
> 
> 
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