直接在 AWK 中设置 BASH 环境变量（在 AWK one-liner 中）
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Setting a BASH environment variable directly in AWK (in an AWK one-liner)
提问by Elliott
I have a file that has two columns of floating point values. I also have a C program that takes a floating point value as input and returns another floating point value as output.
我有一个包含两列浮点值的文件。我还有一个 C 程序，它将一个浮点值作为输入并返回另一个浮点值作为输出。
What I'd like to do is the following: for each row in the original, execute the C program with the value in the first column as input, and then print out the first column (unchanged) followed by the second column minus the result of the C program.
我想做的是以下内容：对于原始中的每一行，以第一列中的值作为输入执行 C 程序，然后打印出第一列（未更改），然后是第二列减去结果C程序的。
As an example, suppose c_program returns the square of the input and behaves like this:
例如，假设 c_program 返回输入的平方，其行为如下：
$ c_program 4
16
$
$ c_program 4
16
$
and suppose data_file looks like this:
并假设 data_file 看起来像这样：
1 10
2 11
3 12
4 13
1 10
2 11
3 12
4 13
What I'd like to return as output, in this case, is
在这种情况下，我想作为输出返回的是
1 9
2 7
3 3
4 -3
1 9
2 7
3 3
4 -3
To write this in really sketchy pseudocode, I want to do something like this:
为了用非常粗略的伪代码编写它，我想做这样的事情：
awk '{print $1, $2 - `c_program $1`}' data_file
awk '{print $1, $2 - `c_program $1`}' 数据文件
But of course, I can't just pass $1, the awk variable, into a call to c_program. What's the right way to do this, and preferably, how could I do it while still maintaining the "awk one-liner"? (I don't want to pull out a sledgehammer and write a full-fledged C program to do this.)
但当然，我不能只将 awk 变量 $1 传递到对 c_program 的调用中。这样做的正确方法是什么，最好是如何在保持“awk one-liner”的同时做到这一点？（我不想拿出大锤并编写一个成熟的 C 程序来做到这一点。）
回答by ghostdog74
you just do everything in awk
你只是用awk做所有事情
awk '{cmd="c_program "; cmd|getline l;print ,-l}' file
回答by Sjoerd
This shows how to execute a command in awk:
这显示了如何在 awk 中执行命令：
ls | awk '/^a/ {system("ls -ld " )}'
You could use a bash script instead:
您可以改用 bash 脚本：
while read line
do
FIRST=`echo $line | cut -d' ' -f1`
SECOND=`echo $line | cut -d' ' -f2`
OUT=`expr $SECOND \* 4`
echo $FIRST $OUT `expr $OUT - $SECOND`
done
回答by msw
The shell is a better tool for this using a little used feature. There is a shell variable IFSwhich is the Input Field Separator that sh uses to split command lines when parsing; it defaults to <Space><Tab><Newline>which is why ls foois interpreted as two words.
shell 是一个更好的工具，它使用了一个很少使用的功能。有一个shell变量IFS，是sh在解析时用来分割命令行的Input Field Separator；它默认为<Space><Tab><Newline>which is whyls foo被解释为两个词。
When setis given arguments notbeginning with -it sets the positional parameters of the shell to the contents of the arguments as split via IFS, thus:
当set给出的参数不以-它开头时，它会将 shell 的位置参数设置为通过 IFS 拆分的参数内容，因此：
#!/bin/sh
while read line ; do
set $line
subtrahend=`c_program `
echo `expr - $subtrahend`
done < data_file
回答by Paused until further notice.
Pure Bash, without using any external executables other than your program:
纯 Bash，不使用除程序以外的任何外部可执行文件：
#!/bin/bash
while read num1 num2
do
(( result = $(c_program num2) - num1 ))
echo "$num1 $result"
done
回答by Hai Vu
As others have pointed out: awk is not not well equipped for this job. Here is a suggestion in bash:
正如其他人指出的那样：awk 并不适合这项工作。这是 bash 中的一个建议：
#!/bin/sh
data_file=
while read column_1 column_2 the_rest
do
((result=$(c_program $column_1)-$column_2))
echo $column_1 $result "$the_rest"
done < $data_file
Save this to a file, say myscript.sh, then invoke it as:
将它保存到一个文件中，比如 myscript.sh，然后调用它：
sh myscript.sh data_file
The read command reads each line from the data file (which was redirected to the standard input) and assign the first 2 columns to $column_1 and $column_2 variables. The rest of the line, if there is any, is stored in $the_rest.
read 命令从数据文件（已重定向到标准输入）中读取每一行，并将前 2 列分配给 $column_1 和 $column_2 变量。该行的其余部分（如果有）存储在 $the_rest 中。
Next, I calculate the result based on your requirements and prints out the line based on your requirements. Note that I surround $the_rest with quotes to reserve spacing. Failure to do so will result in multiple spaces in the input file to be squeezed into one.
接下来，我根据您的要求计算结果并根据您的要求打印出该行。请注意，我用引号将 $the_rest 括起来以保留间距。如果不这样做，将导致输入文件中的多个空格被压缩为一个。
