如何grep包含一个可选单词？

Question

我使用以下grep查询来查找VB源文件中的函数的出现.

    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 -

   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

你可以用a \?做一些可选的东西:

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

在这种情况下,包含字符串"static"的前一组是可选的(即可以发生0或1次).

@CodeBlue是文字？。当您以这种方式调用`grep`时，它会使用BRE（基本正则表达式）。在BRE中，您需要转义许多“高级”表达式的元字符。如另一个答案中所述，如果您通过了-E，那么您就不必转义它（实际上，转义它会使它与文字？匹配！）。 (2认同)

Answer 2

使用grep时,基数明智:

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

考虑下面的例子(其中非常字代表了你的静态):

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,我们要求'非常'字为零或一次:

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

正如你猜测的那样,我邀请你使用egrep而不是grep(你可以尝试grep -E,用于扩展正则表达式).