问题
My objective is to match email addresses that belong to the Yahoo! family of domains. In *nix systems (I will be using Ubuntu), what are the benefits and drawbacks to any one of these methods for matching the pattern?
And if there is another, more elegant solution that I haven't been capable of imagining, please share.
Here they are:
- Use
grepwith option-i:
grep -Ei "@(yahoo|(y|rocket)mail|geocities)\.com"
- Translate characters to all upper case or lower case then
grep:
tr [:upper:] [:lower:] < /path/to/file.txt | grep -E "@(yahoo|(y|rocket)mail|geocities)\.com"
- Include a character set for each character in the pattern (the below would of course not match something like "@rOcketmail.com", but you get the idea of what it would become if I checked each character for case):
grep -E "@([yY]ahoo|([yY]|[rR]ocket)[mM]ail|[gG]eo[cC]ities)\.[cC][oO][mM]" /path/to/file.txt
回答1:
grep -i turned out to be significantly slower than translating to lowers before grepping, so I ended up using a variation of #2.
Thanks @mike-w for reminding me that a simple test goes a long way.
来源：https://stackoverflow.com/questions/22924548/what-is-the-most-efficient-case-insensitive-grep-usage