awk从文件中读取特定列 [英] awk to read specific column from a file

问题描述

我有一个小问题，希望能帮助我解决这个问题.

I have a small problem and I would appreciate helping me in it.

总而言之，我有一个文件:

In summary, I have a file:

1,5,6,7,8,9

2,3,8,5,35,3

2,46,76,98,9

我需要从中读取特定行并将其打印到另一个文本文档中.我知道我可以使用( awk'{print"$ 2""$ 3"}')彼此相邻地打印第二和第三列.但是，我需要使用两个语句作为( awk'{print"$ 2"}'>> file.text )然后是( awk'{print"$ 3"}''>> file.text )，但这两列将显示在彼此下方而不是彼此相邻.

I need to read specific lines from it and print them into another text document. I know I can use (awk '{print "$2" "$3"}') to print the second and third columns beside each other. However, I need to use two statement as (awk '{print "$2"}' >> file.text) then (awk '{print "$3"}' >> file.text), but the two columns would appear under each other and not beside each other.

如何使它们并排出现?

推荐答案

如果您必须在单独的过程中提取列，请使用 粘贴 将它们缝合在一起.我假设您的shell是bash/zsh/ksh，并且我假设示例输入中的空白行不应该存在.

If you must extract the columns in separate processes, use paste to stitch them together. I assume your shell is bash/zsh/ksh, and I assume the blank lines in your sample input should not be there.

paste -d, <(awk -F, '{print $2}' file) <(awk -F, '{print $3}' file)

产生

5,6
3,8
46,76

没有流程替代项:

awk -F, '{print $2}' file > tmp1
awk -F, '{print $3}' file > tmp2
paste -d, tmp1 tmp2 > output

---

根据您的答案进行更新:

---

Update based on your answer:

初次出现时，这是一个令人困惑的设置.这行得通吗?

On first appearance, that's a confusing setup. Does this work?

for (( x=1; x<=$number_of_features; x++ )); do
    feature_number=$(sed -n "$x {p;q}" feature.txt)
    if [[ -f out.txt ]]; then
        cut -d, -f$feature_number file.txt > out.txt
    else
        paste -d, out.txt <(cut -d, -f$feature_number file.txt) > tmp &&
        mv tmp out.txt
    fi
done

那必须多次读取file.txt文件.显然，只需要阅读一次就会更有效:

That has to read the file.txt file a number of times. It would clearly be more efficient to only have to read it once:

awk -F, -f numfeat=$number_of_features '
    # read the feature file into an array
    NR==FNR {
        colno[++i] = $0
        next
    }

    # now, process the file.txt and emit the desired columns
    {
        sep = ""
        for (i=1; i<=numfeat; i++) {
            printf "%s%s", sep, $(colno[i])
            sep = FS
        }
        print ""
    }
' feature.txt file.txt > out.txt

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