Bash set_var / unset_var functions

set_vars.sh

#!/bin/bash                                                                     
# function `set_var` sets a variable with a possiblity to restore previous      
# value back with `unset_var`                                                   
#                                                                               
# Can be used to safely initialize/uninitialize environment in python           
# virtualenvwrapper and friends                                                 
#                                                                               
#roman@home:~$ foo=1                                                            
#roman@home:~$ set_var foo 2                                                    
#roman@home:~$ set_var bar 3                                                    
#roman@home:~$ echo $foo $bar                                                   
#2 3                                                                            
#roman@home:~$ unset_var foo                                                    
#roman@home:~$ unset_var bar                                                    
#roman@home:~$ echo $foo $bar                                                   
#1                                                                              
                                                                                
                                                                                
function set_var() {                                                            
    export OLD_$1=${!1}                                                         
    export $1=$2                                                                
}                                                                               
                                                                                
function unset_var() {                                                          
    old_var_name="OLD_$1"                                                       
    test -z "$old_var_name" && unset $1 || export $1=${!old_var_name}           
    unset OLD_$1                                                                
}