Using dot or "source" while calling another script - what is the difference?

Question

Let's take a little example:

$ cat source.sh
#!/bin/bash
echo "I'm file source-1"

. source-2.sh

And:

$ cat source-2.sh
#!/bin/bash
echo "I'm file source-2"

Now run:

$ ./source.sh
I'm file source-1
I'm file source-2

If I'll change the call of the second file in first:

$ cat source.sh
#!/bin/bash
echo "I'm file source-1"

source source-2.sh

It will have the same effect as using dot.

What is difference between these methods?

Answer 1

There is no difference.

From the manual:

source

source filename

A synonym for . (see Bourne Shell Builtins).

Answer 2

The only difference is in portability.

. is the POSIX-standard command for executing commands from a file; source is a more-readable synonym provided by Bash and some other shells. Bash itself, however, makes no distinction between the two.