I was reading though this other question which has some really good regex's for the job but as far as I can see non of them work with BASH commands as BASH commands don't support such complex rexeg's.
if echo "http://www.google.com/test/link.php" | grep -q '(https?|ftp|file)://[-A-Z0-9\+&@#/%?=~_|!:,.;]*[-A-Z0-9\+&@#/%=~_|]'; then
echo "Link valid"
else
echo "Link not valid"
fi
But this doesn't work as grep -q doesn't work ...
Edit, ok I just realised that grep had an "extended-regex" (-E) option which seems to make it work. But if anyone has a better/faster way I would still love to here about it.
The following works in Bash >= version 3.2 without using grep:
regex='(https?|ftp|file)://[-[:alnum:]\+&@#/%?=~_|!:,.;]*[-[:alnum:]\+&@#/%=~_|]'
string='http://www.google.com/test/link.php'
if [[ $string =~ $regex ]]
then
echo "Link valid"
else
echo "Link not valid"
fi
I simplified your regex by using [:alnum:] which also matches any alphanumeric character (e.g. Э or ß), but support varies by the underlying regex library. This is another potential simplification which uses + instead of * and a repeated sequence (although your second sequence is different from the first).
regex='(https?|ftp|file)://[-[:alnum:]\+&@#/%?=~_|!:,.;]+'