How to append text to a file multiple times without repeating the text file header

[andrew .hbeechey]

I am new to moustache and finding it so easy to use and it saves me so much time.

I do have a problem i cannot resolve as follows

i have a text file that has some standard fixed text as a header, and over time

i need to execute a moustache template to append text at the bottom of the text file.

the problem is each time i try to append some text in this way, the entire files orignal content is duplicated.

is there a way to have moustache simply add text at the bottom of a file and leave the rest of the file untouched