Extract string from string using RegEx in the Terminal [duplicate]

echo 'first url, second url, third url' | sed 's/.*second//'

Edit: I misunderstood. Better:

echo 'first url, second url, third url' | sed 's/.*second \([^ ]*\).*/\1/'

or:

echo 'first url, second url, third url' | perl -nle 'm/second ([^ ]*)/; print $1'