insert bash variable into perl search and replace

Question

in my bash script i look for text inside a file and replace it with a variable from my bash script. I couldn't get the variable to be recognized by the perl command. any ideas?

mybash.bash:

#! /bin/sh
let "myNum=2"# myNum could be any integer
perl -pi -e 's/ABCD\d/ABCD$myNum/g' ./textfile.txt

textfile.txt:

'ABCD0' gets replace with 'ABCD' with above script

Answer 1

Use double quotes so as to enable interpolation of variables:

perl -pi -e "s/ABCD\d/ABCD$myNum/g" ./textfile.txt
           ^^^                   ^^^