如何匹配awk变量中给定的模式?

问题描述

我想从管道分隔文件中提取存在某些模式的子字符串，因此我在下面的命令中使用了

I want to extract a substring where certain pattern exist from pipe separated file, thus I used below command,

awk -F ":" '/REWARD REQ. SERVER HEADERS/{print $1, $2, $3, $4}' sample_profile.txt

在这里，"REWARD REQ.服务器头"是一种模式，可以在文件中进行搜索，并将其前4个部分打印在冒号分隔的行上.

Here, 'REWARD REQ. SERVER HEADERS' is a pattern which is to be searched in the file, and print its first 4 parts on a colon separated line.

现在，我想发送bash变量作为模式.因此我使用了下面的命令，但是它不起作用.

Now, I want to send bash variable to act as a pattern. thus I used below command, but it's not working.

awk -v pat="$pattern" -F ":" '/pat/{print $1, $2 , $3, $4 } sample_profile.txt

如何在单个awk命令中使用-v和-F?

How can I use -v and -F in a single awk command?

推荐答案

此处的问题与-F无关.

问题是当您想将pat用作变量时使用/pat/.如果您说/pat/，则awk会将其理解为文字"pat"，因此它将尝试匹配包含字符串"pat"的行.

The problem is the usage of /pat/ when you want pat to be a variable. If you say /pat/, awk understands it as a literal "pat", so it will try to match those lines containing the string "pat".

如果要通过变量提供模式，则需要使用~这样:

If you want to provide the pattern through a variable, you need to use ~ as this:

 awk -v pat="$pattern" '$0 ~ pat'

总共，您的代码应为:

awk -v pat="$pattern" -F ":" '$0~pat{print $1, $2, $3, $4 }' file
#                             ^^^^^^

---

查看示例:

---

See an example:

提供此文件:

$ cat file
hello
this is a var
hello bye

让我们寻找包含"hello"的行:

Let's look for lines containing "hello":

$ awk '/hello/' file
hello
hello bye

现在让我们尝试按照您的操作方式查找变量中包含的"pat":

Let's now try looking for "pat", contained in a variable, the way you were doing it:

$ awk -v pat="hello" '/pat/' file
$                                    # NO MATCHES!

现在让我们使用$0 ~ pat表达式:

Let's now use the $0 ~ pat expression:

$ awk -v pat="hello" '$0~pat' file
hello                                 # WE MATCH!
hello bye

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当然，您可以使用此类表达式来匹配一个字段并说出awk -v pat="$pattern" '$2 ~ pat' file，依此类推.

---

Of course, you can use such expressions to match just one field and say awk -v pat="$pattern" '$2 ~ pat' file and so on.

来自 GNU Awk用户指南→3.1如何使用正则表达式:

GNU Awk用户指南→3.6使用动态正则表达式:

BEGIN { digits_regexp = "[[:digit:]]+" }
$0 ~ digits_regexp    { print }

这会将digits_regexp设置为描述一个或多个数字的正则表达式， 并测试输入记录是否与此正则表达式匹配.

This sets digits_regexp to a regexp that describes one or more digits, and tests whether the input record matches this regexp.

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