如何匹配awk变量中给定的模式? [英] How to match a pattern given in a variable in awk?
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" '$0~pat' file
hello # WE MATCH!
hello bye
当然，您可以使用此类表达式来匹配一个字段并说出awk -v pat="$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.
当正则表达式用斜杠括起来(例如/foo/)时，我们将其称为正则表达式常量，就像5.27是数字常量而"foo"是字符串常量一样.
When a regexp is enclosed in slashes, such as /foo/, we call it a regexp constant, much like 5.27 is a numeric constant and "foo" is a string constant.
〜"或！〜"运算符的右侧不必是正则表达式 常数(即，斜线之间的字符串).可能是任何 表达.如果满足以下条件，则对表达式求值并将其转换为字符串 必要的;然后，将字符串的内容用作正则表达式.一种 以这种方式计算的正则表达式称为动态正则表达式或 正则表达式:
The righthand side of a ‘~’ or ‘!~’ operator need not be a regexp constant (i.e., a string of characters between slashes). It may be any expression. The expression is evaluated and converted to a string if necessary; the contents of the string are then used as the regexp. A regexp computed in this way is called a dynamic regexp or a computed regexp:
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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