本文介绍了与fd嵌套同时读取循环的处理方法,对大家解决问题具有一定的参考价值,需要的朋友们下面随着小编来一起学习吧!
问题描述
我正在尝试从嵌套循环中的两个不同输入读取数据,但没有成功.对于这个问题,我一直遵循的最佳答案,还查看了文件描述符页面高级Bash脚本指南中的内容.
I'm trying to read from two different inputs in nested loops without success. I've followed the best answer on this question and also took a look at the file descriptors page of the Advanced Bash-Scripting Guide.
#!/bin/bash
while read line <&3 ; do
echo $line
while read _line <&4 ; do
echo $_line
done 4< "sample-2.txt"
done 3< "sample-1.txt"
sample-1.txt的内容
Foo
Foo
sample-2.txt的内容
Bar
Bar
预期产量
Foo
Bar
Bar
Foo
Bar
Bar
我得到的输出
Foo
Bar
推荐答案
您的文本文件不以换行符结尾:
Your text files do not end with newlines:
$ printf 'Foo\nFoo' > sample-1.txt
$ printf 'Bar\nBar' > sample-2.txt
$ bash tmp.sh
Foo
Bar
$ printf '\n' >> sample-1.txt
$ printf '\n' >> sample-2.txt
$ bash tmp.sh
Foo
Bar
Bar
Foo
Bar
Bar
如果
read
到达文件末尾而没有看到换行符,则退出状态为非零.可以解决此问题,但是最好确保文本文件正确以换行符结尾.
read
has a non-zero exit status if it reaches the end of the file without seeing a newline character. There's a hack to work around that, but it's better to ensure that your text files correctly end with a newline character.
# While either read is successful or line is set anyway
while read line <&3 || [[ $line ]]; do
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