Question

if [ '`echo "$url" | grep (\.tar\.gz|\.tar\.bz2|\.zip|\.rar|\.7z)$`' ] ; then

syntax error, I just want to check file extension.

Answer 1

First of all, you need to remove the '' as otherwise the test is just a string that always evaluates to true. You need to put the regex in quotes as parentheses are interpreted by bash. You also need to use egrep (equivalent to grep -E).

if [ `echo "$url" | egrep "(\.tar\.gz|\.tar\.bz2|\.zip|\.rar|\.7z)$"` ] ; then

You can also shorten the regex by factoring the . out of the group and grouping tar.{gz,bz2}:

if [ `echo "$url" | egrep "\.(tar\.(gz|bz2)|zip|rar|7z)$"` ] ; then

For future, please take note of the error bash gives you which tells you quite a lot: bash: syntax error near unexpected token ( suggests that the error is around the (, which I’ve just shown you is exactly where the error lies.

Jonathan’s answer offers more tips on improving the test.