You need the -P switch for Perl Compatible Regular Expressions (PCRE).

Try:

grep -P "disable|enable" fail.log


Without it, grep uses POSIX Basic Regular Expressions, which have inconsistent escaping and less features.

How to grep words in a file?
China's Guangzhou Evergrande FC set up a mouthwatering FIFA Club World Cup semi-final against European champions Bayern Munich after seeing off Egypt's Al Ahly 2-0. And Guangzhou Evergrande FC challenges Bayern Munich on their newly released posters with this slogan: Where Amazing Happens. 



I am wondering if this slogan is a right expression. Amazing is an adjective without doubt, then how could it be used alone as a subject? I have thought this over and now I guess maybe it is acceptable using some simplified, less-grammatical expressions for news titles and slogans, isn't it? 
