Replacing a String from all the files with the value from text file

Question

I have a text file named abcd.txt which has content dfunsufngsufspdfnsufbhpsdubf

I have multiple php files, py files in a folder names /home/admin/temp All the files have a string replace-me

How can I replace this? I tried using the below script

NODE=1
BOY="/home/opc/firewall"
GIRL="$BOY/full/temp-$NODE"

grep -rl 'replace-me' $GIRL | xargs sed -i "s/replace-me/$(cat $GIRL/abcd3.txt)/g";

I'll be using this in a big script. Someone please help me in such case