AWK-以指令执行字串吗? [英] AWK - execute string as command?

问题描述

此命令将打印:

$ echo "123456789" | awk '{ print substr ($1,1,4) }'
1234

是否可以将字符串作为命令执行?例如，以下命令:

Is it possible to execute a string as command? For example, this command:

echo "123456789" | awk '{a="substr"; print a ($1,1,4) }'

结果:

$ echo "123456789" | awk '{a="substr"; print a ($1,1,4) }'
awk: {a="substr"; print a ($1,1,4) }
awk:                               ^ syntax error

$ cat tst.awk 
function my_substr(x,y,z) { return substr(x,y,z) }

{ a="my_substr"; print @a($1,1,4) }
bolek@bolek-desktop:~/Pulpit$ echo "123456789" | gawk -f tst.awk
gawk: tst.awk:3: { a="my_substr"; print @a($1,1,4) }
gawk: tst.awk:3:                        ^ nieprawidłowy znak '@' w wyrażeniu
bolek@bolek-desktop:~/Pulpit$ 

推荐答案

您可以使用间接函数调用通过GNU awk中的变量来调用用户定义的函数，请参见

You can call user-defined functions via variables in GNU awk using indirect function calls, see http://www.gnu.org/software/gawk/manual/gawk.html#Indirect-Calls

$ cat tst.awk
function foo() { print "foo() called" }
function bar() { print "bar() called" }

BEGIN {
   the_func = "foo"
   @the_func()

   the_func = "bar"
   @the_func()
}
$ gawk -f tst.awk
foo() called
bar() called

不幸的是，由于内部实现问题，如果要以这种方式调用内置函数，则需要为每个函数编写一个包装器:

Unfortunately due to internal implementation issues, if you want to call builtin functions that way then you need to write a wrapper for each:

$ cat tst.awk
function my_substr(x,y,z) { return substr(x,y,z) }

{ a="my_substr"; print @a($1,1,4) }
$ echo "123456789" | gawk -f tst.awk
1234

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