As near as I can tell, Perl regex is egrep with slightly more features. For instance, Perl allows $1 $2 etc for matched values in parentheses, while egrep does not (though \1 \2 works in both? - see syntax). Perl also allows min/max number of matches with {4,5}, while egrep does not. Bottom line is that your egreps should hopefully work the same running through Perl regex, though Perl regex might not work running through egrep.