How to execute Vim commands from commands.vim file to my text mydata.txt file?

Hi,
using Vim 7.4 on Windows 7. I have a text file mydata.txt where is the text. I need to execute Vim commands on this data to transform data in file to my desired content. Because data in mydata.txt file is changed very frequently I would like to store Vim commands in separate file e.g. commands.vim and then execute those commands on mydata.txt file.

Searching the web and the only solution that I have come into was the following.

1. Save bellow comment to commands.vim file:
===============
:%s/ship/vessel/ge
:%s/What/That/ge

for line in getline(1, 2)
let @a = line
@a
endfor
===============

2. Save bellow content to mydata.txt file.
===============
This is one big ship. What ship?
===============

3. Open mydata.txt file with Vim and execute command:
:source commands.vim

4. The result after executed above command is:
===============
This is one big vessel. That vessel?
===============

This is exactly what I want as a result in mydata.txt file, but what I don't like is I get the following error:
===============
Error detected while processing C:\commands.vim file:
line 6:
E492: Not an editor command: This is one big vessel. That vessel?
===============

Is there a way to avoid the error message? Commands.vim file does what I want, but how to remove annoying error?
Thanks

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