Imagine you have two shell scripts in the same directory.

test1.sh:

#!/bin/bash

echo "I am test1"
cp test2.sh test1.sh

test2.sh:

#!/bin/bash

echo "I am test2"
cp test2.sh test1.sh

echo "This should not get printed"

Now run test1.sh. What do you expect the output to be?

I’d imagine that bash would run a copy of test1.sh in memory, and as a result of that execution, test1.sh would be replaced with test2.sh at the end of execution. But I would be wrong. This is the output I get after running test1.sh:

$ ./test1.sh 
I am test1
This should not get printed

What the?