General :: Variables In Text File - How To Get Values When Printing Out

I'm doing some bash-scripting and want to be able to print some text (just plain text) files into the new bash-scripts, created within a loop. Here's a short example of what I do:

Code:
# main bash script #
#!/bin/bash
##Filename
variable1=10
for ((j=0;j<=40;j+=1))
do
## Create another bash-script
echo "#!/bin/bash" >> bash_script_$j
... some stuff...
cat file1.txt >> bash_script_$j
... some more stuff...
done
where the text file (file1.txt) I want to print in the the new bash script looks something like:

Code:
# file1.txt #
...some stuff...
logsave log some_program($variable1)
mv output_$j folder_$j/
... some more stuff...

I.e, the text file contains variables such as "$j", "$variable1" etc that are undefined. Doing the above works for creating new bash scripts (bash_script_1 - bash_script_40) but the variables are not determined. I would like, if possible, to somehow print the text in file1.txt into the new bash-scripts with the variables determined, i.e:

Code:
# bash_script_1 #
...some stuff...
logsave log some_program(10)
mv output_1 folder_1/
... some more stuff...

The text files I read are quite extensive so I would really prefer not having to paste them into the FOR-loop directly.