Grep 只能忽略病例

Grep 在同时使用——忽略大小写和—— only-match 选项时失败。 例如:

$ echo "abc" | grep -io abc
abc
$ echo "ABC" | grep -io abc
$

但是

$ echo "abc" | grep -i abc
abc
$ echo "ABC" | grep -i abc
ABC

根据手册:

   -o, --only-matching
Show only the part of a matching line that matches PATTERN.
-i, --ignore-case
Ignore case distinctions in both the PATTERN and the input files.

是 grep 的错误还是我没拿到地图页面？

我使用的是 MacOSX10.6.8和

$ grep --version
grep (GNU grep) 2.5.1

找到这个链接: http://lists.gnu.org/archive/html/bug-gnu-utils/2003-11/msg00040.html

当然，也可以像 grep -o [aA][bB][cC]那样使用变通方法，但是这似乎不是一个好的选择。

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小开

It could be a problem in your version of grep.

Your test cases are working correctly here on my machine:

$ echo "abc" | grep -io abc
abc
$ echo "ABC" | grep -io abc
ABC

And my version is:

$ grep --version
grep (GNU grep) 2.10
小开

I'd suggest that the -i means it does match "ABC", but the difference is in the output. -i doesn't manipulate the input, so it won't change "ABC" to "abc" because you specified "abc" as the pattern. -o says it only shows the part of the output that matches the pattern specified, it doesn't say about matching input.

The output of echo "ABC" | grep -i abc is ABC, the -o shows output matching "abc" so nothing shows:

Naos:~ mattlacey$ echo "ABC" | grep -i abc | grep -o abc
Naos:~ mattlacey$ echo "ABC" | grep -i abc | grep -o ABC
ABC
小开
最佳答案

This is a known bug on the initial 2.5.1, and has been fixed in early 2007 (Redhat 2.5.1-5) according to the bug reports. Unfortunately Apple is still using 2.5.1 even on Mac OS X 10.7.2.

You could get a newer version via Homebrew (3.0) or MacPorts (2.26) or fink (3.0-1).

Edit: Apparently it has been fixed on OS X 10.11 (or maybe earlier), even though the grep version reported is still 2.5.1.

小开

If your grep -i does not work then try using tr command to convert the the output of your file to lower case and then pipe it into standard grep with whatever you are looking for. (it sounds complicated but the actual command which I have provided for you is not !).

Notice the tr command does not change the content of your original file, it just converts it just before it feeds it into grep.

1.here is how you can do this on a file 

tr '[:upper:]' '[:lower:]' <your_file.txt|grep what_ever_you_are_searching_in_lower_case

2.or in your case if you are just echoing something

echo "ABC"|tr '[:upper:]' '[:lower:]' | grep abc

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