Can I use my own variables within awk and sed for example:
I've written a while loop with a counter $i and I want to use the value of $i within sed and awk to edit certain lines of text within a data file.

I want to use :
sed '1s/$/texthere/g' birthday.csv
Like this:
sed '$is/$/$age/g' birthday.csv
but it only displays the name of the variable not the value it contains

$age is the result of a calculation created within the while loop that I would like to append to the end of each line.

Any help is greatly appreciated

You have to read up on the (sometimes strange) rules about quoting and variable substitution in various shells.

Try say
sed $i's/$/'$age'/g' birthday.csv
Or maybe
sed "${i}s/$/${age}/g" birthday.csv

Worked great thanks very much