Question

4

regex search works with `grep -E` but not with bash script?

rated 0 times [ 4] [ 0] / answers: 1 / hits: 3915 / 3 Years ago, wed, june 9, 2021, 11:13:52

I use the same regex with grep and it gives me a match but when doing it in a bash script, it return no match.

Test String(part of the file testregex.txt):

<a href="/os_x_lynx-wallpapers.html"><p>OS X Lynx</p><img src="/thumbs/os_x_lynx-t1.jpg"alt="OS X Lynx" class="thumb_img" width="270" height="169"/></a></div><div style="float:right;margin-right:13px;"></div></div>

This command correctly matches the highlighted part(and a few more):

grep -E '<img src="[^"]*.jpg"' testregex.txt

But this bash script returns no match:

page=$(<testregex.txt)



if [[ $page =~ '<img src="[^"]*.jpg"' ]]; then

    echo $1

    echo "match found"

else

    echo "match not found!"

fi

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brailloni

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1 Year ago

answered 3 Years ago fulerio · Accepted Answer

In the case =~ operator, just don't use quotes for the right operator. This is considered an extended regular expression so in this case the single quotes will be part from he regular expression. So, using single quotes, a string like '<img src="/thumbs/os_x_lynx-t1.jpg"' (which contain also single quotes around it) will be found. See Meaning of “=~” operator in shell script.

Also, you must to escape any special character in your regex (quotes, spaces, shell redirection - <):

#!/bin/bash

page=$(<testregex.txt)



if [[ $page =~ <img src="[^"]*.jpg" ]]; then

    echo $1

    echo "match found"

else

    echo "match not found!"

fi

Apart of =~, you can use in your script your original command which uses grep:

#!/bin/bash



if grep -qE '<img src="[^"]*.jpg"' testregex.txt ; then

    echo $1

    echo "match found"

else

    echo "match not found!"

fi

In this case I used -q option for grep to not write anything to standard output and to exit immediately if any match is found.