将bash变量作为模式传递给awk [英] Passing bash variable as a pattern to awk

问题描述

我想知道如何将bash variable作为pattern传递给awk. 我已经阅读了几个Q/A，它们往往回答相同的问题，但是，没有一个解决了我的问题(可能是我遗漏了一些东西！).

I would like to know how to pass a bash variable as a pattern to awk. I have read several Q/As which tend to answer the same question, however, none of them solved my problem (probably, I am missing something!).

我有几个这样的文件:

1   9909    23121  
1   23121   561510  
3   75879819    75902940  
3   75902940    75916152  
4   75916152    75982212  
3   75982212    75998727  
22  82964754    83232297 
X   59962662    60745473

，我想创建不同的文件，每个文件都包含相同的起始模式，我只想提取第2列，例如一个文件包含所有以第一个开头的行的第2列，另一个文件包含所有以X开头的行的第2列，等等.

and I want to create different files each containing same starting pattern and I only want to extract column 2 e.g. a file containing column 2 of all the rows starting with one, the other file containing column 2 of the rows starting with X etc.

我的代码如下:

for x in *.CNVs; do  
   for y in `seq 22` X Y; do  
        awk '/^$y/ {print $2}' $x > freec_${x}_${y}_st.txt;  
   done;  
done;  

我也尝试过使用-v选项，例如:

I have also tried using -v option like this:

for x in *.CNVs; do  
    for y in `seq 22` X Y; do  
        awk -v pattern="{$y}" '/^pattern/ {print $2}' $x > freec_${x}_${y}_st.txt;  
    done;  
done;

我没有收到任何错误，所有文件均已创建；但是，它们都是空的！任何建议，不胜感激！

I don't get any error, all the files are created; however, they are all empty! Any suggestion is much appreciated!

[编辑] 我发现了使用grep的更整洁的方式(以前，我认为它不能通过grep来完成！):

[Edit] I found a neater way using grep (before, I was thinking that it cannot be done by grep!):

for x in *.CNVs; do
    for y in `seq 22` X Y; do
        grep "^${y}\s" $x | cut -f2 > ${x}_${y}_st.txt;
    done;
done;

使用grep很有帮助，因为通过使用\s，我可以区分以2、21和22等开头的行.

Using grep is helpful since by using \s, I can discriminate between line starting with 2, 21 and 22 etc.

推荐答案

变量未使用正则表达式文字(/.../)进行扩展.您需要使用~运算符和字符串文字.

Variables aren't expanded in regexp literals (/.../). You need to use the ~ operator and string literals.

awk -v pattern="$y" '$0 ~ "^"pattern {print $2}' "$x" > "freec_${x}_${y}_st.txt"

您还需要注意任何模式元字符/等.在模式中.

You also need to be careful with any pattern metacharacters/etc. in the pattern.

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