Re: regex, negations, grep, find and replace (a few questions)

(I'm changing some parts of the message due to spam filters on the server rejecting the message: substitute "**" with "tt", and "@@" with "a ")

jameshanley39@xxxxxxxxxxx wrote:

Here is a regex to match a link. Testing the regex using echo and
piping it
$ echo "abc<@@href=\"h**p://www.blah.com\">click here</a>" | grep -P
'<@@href="h**p://www.*>.*</a>'

a)
A problem is that grep works line by line. So
- it includes the abc before the link

Not if you use -o.

- if the pattern/link were broken over 2 lines, it would not match
(other tests suggest that)

I really don`t want it to include the abc at the beginning of the line
where the pattern matches.

Is there anything like grep that does not have this problem/feature ?
or where that problem/feature can be turned off?

Use -o (man grep). For the multi-line problem, just remove the newline characters before piping the text to grep, eg

echo $text | tr -d '\n' | grep 'your_pattern'

BTW, your pattern is not correct. First, it does not match links whose url does not start with "h**p://www". Second, due to sed "greedy" match behavior, if you had a text with more than one link, it would match from the beginning of the first link to the end of the last. Something like this would probably be a better pattern:

'<@@href="h**p://www[^>]*">[^<]*</a>'

b)
I heard that it is hard to negate a regex.
So, alternatives,
some programming languages provide advanced features to negate it.
Also, programs, like grep, allow you to negate it. (grep -v)

But grep does not let you do a replace. And On the negation of a
regex.
Which programs would , and how?

sed would be able to do this and much more else.
.

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