Defining common variables across multiple scripts?

Question

I have a number of Bash and Perl scripts which are unrelated in functionality, but are related in that they work within the same project. The fact that they work in the same

Answer 1

Define environments variables : user level : in your ~/.profile or ~/.bash_profile or ~/.bash_login or ~/.bashrc system level : in /etc/profile or /etc/bash.bashrc or /etc/environment

For example add tow lines foreach variable :

FOO=myvalue
export FOO 

To read this variable in bash script :

#! /bin/bash

echo $FOO

in perl script :

#! /bin/perl

print $ENV{'FOO'};

Answer 2

When you run a shell script, it's done in a sub-shell so it cannot affect the parent shell's environment. So when you declare a variable as key=value its scope is limited to the sub-shell context. You want to source the script by doing:

. ./myscript.sh

This executes it in the context of the current shell, not as a sub shell.

From the bash man page:

. filename [arguments]
source filename [arguments]

Read and execute commands from filename in the current shell environment and return the exit status of the last command executed from filename.

If filename does not contain a slash, file names in PATH are used to find the directory containing filename. 

Also you can use the export command to create a global environment variable. export governs which variables will be available to new processes, so if you say

FOO=1
export BAR=2
./myscript2.sh

then $BAR will be available in the environment of myscript2.sh, but $FOO will not.