如何grep包含一个可选单词？

Question

我使用以下grep查询来查找VB源文件中函数的出现次数。

    grep -nri "^\s*\(public\|private\|protected\)\s*\(sub\|function\)" formName.frm

匹配 -

    Private Sub Form_Unload(Cancel As Integer)
    Private Sub lbSelect_Click()
    ...

然而，它错过了像

这样的功能

   Private Static Sub SaveCustomer()

因为那里附加了“静态”字样。如何在grep查询中考虑这个“可选”字？

Answer 1

您可以使用\?制作可选内容：

grep -nri "^\s*\(public\|private\|protected\)\s*\(static\)\?\s*\(sub\|function\)" formName.frm

在这种情况下，前面的组包含字符串＆＃34; static＆＃34;，是可选的（即可能出现0或1次）。

Answer 2

使用grep时，基数明智：

* : 0 or many
+ : 1 or many
? : 0 or 1 <--- this is what you need.

给出以下示例（非常字代表静态）：

I am well
I was well
You are well
You were well
I am very well
He is well
He was well
She is well
She was well
She was very well

如果我们只想要

I am well
I was well
You are well
You were well
I am very well

我们会用'？' （还要注意在“非常”之后仔细放置空格，提到我们要求'非常'一词为零或一次：

egrep "(I|You) (am|was|are|were) (very )?well" file.txt

正如您猜测的那样，我邀请您使用 egrep 而不是 grep （您可以尝试 grep -E ，用于扩展常规表达式）。