[clug] Circumflex

[Kim Holburn]

> On 2017/Aug/20, at 5:33 PM, Bryan Kilgallin (iiNet) via linux <linux at lists.samba.org> wrote:
> 
> Thanks, Eyal:
> 
>> I think that the '\d' notation is a Perl extension, so try
>>     grep -P ^\d'
> 
> I was confused among versions of regular expressions! Discovering by trial and error. So to search for `-' I had to escape it with `\'.

to search for - in grep you can also use '[-]' 

Regular expressions are confusing.  Every language and program has a slightly different set.  And some like grep have 3 different sets!  The full perl reference is here:

http://perldoc.perl.org/perlre.html

Vim uses a different syntax for regex: http://www.vimregex.com/

Python is different again: https://docs.python.org/2/howto/regex.html

Kim

> 
> What Web resource explains standard, extended, and Perl variants?
> 
>> Note that 'egrep' is short for 'grep -E' (extended regex) and you cannot use '-E' and '-P'
>> together as they have conflicting rules.
> Grep highlighted searched characters--while egrep did not.
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