我使用grep -i得更频繁，我发现它比egrep等效的慢，我匹配每个字母的大写或小写：
$ time grep -iq "thats" testfile
real 0m0.041s
user 0m0.038s
sys 0m0.003s
$ time egrep -q "[tT][hH][aA][tT][sS]" testfile
real 0m0.010s
user 0m0.003s
sys 0m0.006s
是否grep -i做额外的测试，egrep不？