为什么我从 grep -oc "foo" 得到不同的答案?文件和 grep -o "foo";档案 |wc -l ?哪个是对的? [英] Why am I getting different answers from grep -oc "foo" file and grep -o "foo" file | wc -l ? Which is correct?

问题描述

这个问题真的说明了一切......我试图找到特定的出现次数大文件中的字符串.
答案是相似的....像 50 000 左右的管道和 49 000 奇数，只有普通的 grep - oc...

The question says it all really... I am trying to find the number of occurences of specific strings in a large file.
The answers are similar.... like 50 000 or so with the pipe and 49 000 odd with just the plain grep - oc...

谁能解释为什么我得到不同的答案，哪个是正确的?

Can anyone explain why I am getting different answers, and which one would be correct?

感谢您的帮助.

推荐答案

在 --only-matching (-o) 模式下 grep 有时会输出多行单匹配行.

In --only-matching (-o) mode grep will sometimes output multiple lines for a single matching line.

alex@yuzu:~$ echo -e "foo
bar
baz"
foo
bar
baz

alex@yuzu:~$ echo -e "foo
bar
baz" | grep -o o  
o
o

但是使用 --count (-c) 它将计算匹配行的数量.

But with --count (-c) it will count the number of matching lines.

alex@yuzu:~$ echo -e "foo
bar
baz" | grep -oc o
1

所以 grep -o o |wc -l 正在计算所有匹配项，即使一行中有多个匹配项.

So grep -o o | wc -l is counting all the matches, even if there is more than one match in a single line.

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