grep - 如何 grep 包含可选单词？

Question

我使用以下 grep 查询来查找 VB 源文件中出现的函数。

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

这匹配 -

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

但是，它错过了以下功能 -

   Private Static Sub SaveCustomer()

因为那里的附加词“静态”。如何在 grep 查询中解释这个“可选”词？

score 25 · Accepted Answer

您可以使用 a\?使某些内容成为可选：

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”的前面的组是可选的（即可能出现 0 次或 1 次）。

score 10 · Accepted Answer

使用 grep 时，基数明智：

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

给定以下示例（这个词代表您的static）：

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

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

我们将使用“？” （还要注意在“very”之后小心放置空格，以提及我们希望“very”这个词出现零次或一次：

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

正如您猜到的那样，我邀请您使用egrep而不是grep（您可以尝试grep -E，用于扩展正则表达式）。

2 回答 2