如何在awk中引用shell变量？

xn_sung

比如：
awk '$1 == "words" {print $2}' file

如果word换成一个变量，该怎样写？

haimming

awk '$1 == "'$words'" {print $2}' file  双单单双

xn_sung

原帖由 haimming 于 2009-6-8 23:31 发表
awk '$1 == "'$words'" {print $2}' file  双单单双

谢谢！还有别的办法吗？别误会，我只是满足一下好奇心:wink:
还有，在别的地方，也可以这样用吗？

比如：awk ' $1 !~ /'$word'/'... 这样可以吗？手上没有linux试，多嘴问一下

还有，这种用法是什么原理啊？

以前都是调用系统命令"echo $..."然后再getline的，土死了

[ 本帖最后由 xn_sung 于 2009-6-8 23:47 编辑 ]

haimming

你搜索 一下吧，这是个经典问题了

yingweixu

建议看一下：
http://www.chinaunix.net/index.p ... read.php?tid=448687

xn_sung

翻了一下awk的手册，贴上来，官方做法呵呵

6.2 Using Shell Variables in Programs

awk programs are often used as components in larger programs written in shell. For example, it is very common to use a shell variable to hold a pattern that the awk program searches for. There are two ways to get the value of the shell variable into the body of the awk program.

The most common method is to use shell quoting to substitute the variable's value into the program inside the script. For example, in the following program:

     echo -n "Enter search pattern: "
     read pattern
     awk "/$pattern/ "'{ nmatches++ }
          END { print nmatches, "found" }' /path/to/data

the awk program consists of two pieces of quoted text that are concatenated together to form the program. The first part is double-quoted, which allows substitution of the pattern variable inside the quotes. The second part is single-quoted.

Variable substitution via quoting works, but can be potentially messy. It requires a good understanding of the shell's quoting rules (see Quoting), and it's often difficult to correctly match up the quotes when reading the program.

A better method is to use awk's variable assignment feature (see Assignment Options) to assign the shell variable's value to an awk variable's value. Then use dynamic regexps to match the pattern (see Computed Regexps). The following shows how to redo the previous example using this technique:

     echo -n "Enter search pattern: "
     read pattern
     awk -v pat="$pattern" '$0 ~ pat { nmatches++ }
            END { print nmatches, "found" }' /path/to/data

Now, the awk program is just one single-quoted string. The assignment ‘-v pat="$pattern"’ still requires double quotes, in case there is whitespace in the value of $pattern. The awk variable pat could be named pattern too, but that would be more confusing. Using a variable also provides more flexibility, since the variable can be used anywhere inside the program—for printing, as an array subscript, or for any other use—without requiring the quoting tricks at every point in the program.