UNIX for Dummies Questions & Answers

sed 's/^*\([A-Z]{3}*$\)/\1 /' <test.txt >results.txt

http://www.example.com/200904/AUS.txt
http://www.example.com/200903/_RUS.txt
http://www.example.com/200902/.FRA.txt

AUS.txt
RUS.txt
FRA.txt

sed 's#.*/[_.]*##' test.txt >results.txt

while read a
do
    echo ${a##*/} | sed 's/^[\. _]//'
done < input.txt > output.txt

echo 'http://www.example.com/200904/.abc1AaAUS.txt' | sed 's#.*/.*\([A-Z]\{3\}[.].*\)#\1#'

> echo http://www.example.com/200904/AUS.txt | sed 's/[A-Z]\{3\}/~&/' | cut -d"~" -f2
AUS.txt