#/bin/bash
filenames=`find ./ -name "filelist.txt"`

callSigns=""

for filename in $filenames
do
    tmp=`cat "$filename" | grep -P -o ';.+?;' | sed 's/;//g' | sort -u`
    callSigns+=${tmp}  
done

echo $callSigns | sed 's/ /\n/g' | sort -u > callSigns.txt