Difference between ./executable and . executable

./executable runs an executable which is in the current working directory. (executable is not enough for that if there is no . in your $PATH, and usually there isn't). In this case, executable can be an elf binary, or a script starting with #!/some/interpreter, or anything you can exec (on Linux it's potentially everything, thanks to binfmt module).

. executable sources a shell script into your current shell, whether it has execute permissions or not. No new process is created. In bash, script is searched according to the $PATH variable. Script may set environment variables which will remain set in your shell, define functions and aliases and so on.

is there a difference between ./executable and source executable?

basic difference is,

./foo.sh      - foo.sh will be executed in a sub-shellsource foo.sh - foo.sh will be executed in current shell

some example could help to explain the difference:

let's say we have foo.sh:

#!/bin/bashVAR=100

source it:

$ source foo.sh $ echo $VAR100

if you :

./foo.sh$ echo $VAR[empty]

another example, bar.sh

#!/bin/bashecho "hello!"exit 0

if you execute it like:

$ ./bar.shhello$

but if you source it:

$ source bar.sh<your terminal exits, because it was executed with current shell>

In the second one you give the path: ./ is the current working directory so it doesn't search in PATH for the executable but in the current directory.

source takes the executable as a parameter and executes it in the current process.