csh:
set a=0
echo "a is $a"
when i do ./my_script.csh output is:
a is
when i do source my_script.csh output is:
a is 0
Why is it so . As i know that ./ execution uses new shell.
check if variable "a" is set in your current shell:
set | grep '^a='
Remember that once you source script to your current shell, all it's global variables are there until unset or you exit the current shell. You may want to start a new shell, source the script, end exit shell to perform valid tests.
I don't know the context of your problem, but you may want to export some key variables to have their copies in every subprocess.
That's right, ./my_script.csh starts a new shell, and uses the #! that you should have at the top of the file to select which shell to run (which should be csh in this case).
source my_script.csh runs the script in the current shell.
If the script is incorrectly run in, for example, the bash shell, set a=0 is not the syntax for setting an environment variable in bash, so the code won't work as you expected, because you're using the wrong shell.
Take a look at the #! at the top of the file. Is it correct?
来源：https://stackoverflow.com/questions/5645854/difference-between-source-and-execution-of-linux-scripts