Assuming you have gnu grep, you can use perl-style regex to do a positive lookbehind:
grep -oP '(?<=GET\s/)\w+' file
If you don’t have gnu grep, then I’d advise just using sed:
sed -n '/^.*GET[[:space:]]\{1,\}\/\([-_[:alnum:]]\{1,\}\).*$/s//\1/p' file
If you happen to have gnu sed, that can be greatly simplified:
sed -n '/^.*GET\s\+\/\(\w\+\).*$/s//\1/p' file
The bottom line here is, you certainly don’t need pipes to accomplish this. grep
or sed
alone will suffice.