为什么unix读时不读最后一行? [英] Why does unix while read not read last line?

问题描述

我的脚本

export IFS=":"

cat hello | while read a b c d; do
    echo $a,$b,$c,$d
done

我的文件hello

1:1:1:1
2:2:2:2
3:3:3:3

我的输出

1,1,1,1
2,2,2,2

如果我在hello中的3:3:3:3之后放置空白行，则输出将变为

If I put a blank line after 3:3:3:3 in hello then the output becomes

1,1,1,1
2,2,2,2
3,3,3,3

任何人都知道如何解决此问题，因此我不需要在hello的末尾插入空白行?

Anyone know how I can fix this problem so I don't need to put a blank line at the end of hello?

推荐答案

发生了什么事，当输入未以换行符终止时，read命令失败.由于文件末尾缺少换行符，因此read失败，因此将跳过while循环的最后一次迭代.

What's happening is, the read command fails when the input is not terminated with a newline. Since the newline character is missing at the end of your file, the read fails, so the last iteration of the while loop is skipped.

如果您不想/不能确保输入文件的末尾有换行符，可以将cat与echo分组以给出外观输入由换行符终止，例如:

If you don't want to / cannot make sure that your input file has a newline at the end, you can group your cat with an echo to give the appearance of an input terminated by newline, for example like this:

{ cat hello; echo; } | while read a b c d; do
    echo $a,$b,$c,$d
done

或类似这样:

(cat hello; echo) | while read a b c d; do
    echo $a,$b,$c,$d
done

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