bash 重定向到 /dev/null: 没有那个文件或目录
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redirect to /dev/null: No such file or directory
提问by Sallyerik
I would like to know if somebody could help me with this error:
我想知道是否有人可以帮助我解决此错误：
wc: Files/Unused-CMA_host.txt: No such file or directory
wc: Files/Unused-CMA_host.txt: 没有那个文件或目录
The file doesn't exist, then I want to redirect the output to /dev/null
该文件不存在，然后我想将输出重定向到 /dev/null
I try with this sentence > /dev/null 2>&1which is working in other case, but not here:
我尝试使用这句话> /dev/null 2>&1，它在其他情况下有效，但不是在这里：
wc -l Files/Unused-CMA_host.txt | awk '{print $1}' > /dev/null 2>&1
wc -l Files/Unused-CMA_host.txt | awk '{print $1}' > /dev/null 2>&1
somebody know why?
有人知道为什么吗？
thanks.
谢谢。
回答by chepner
Redirections apply to individual components of a pipeline, not a pipeline as a whole. In your example, you only redirect awk's standard output. To redirect the standard error and stardard output of the entire pipeline would require a command group such as
重定向适用于管道的各个组件，而不是整个管道。在您的示例中，您只重定向awk的标准输出。要重定向整个管道的标准错误和标准输出将需要一个命令组，例如
{ wc -l Files/Unused-CMA_host.txt | awk '{print }' ; } > /dev/null 2>&1
However, if the file doesn't exist, there won't be any standard output. Perhaps you want to redirect standard error to suppress the error message? Then you can simply use
但是，如果该文件不存在，则不会有任何标准输出。也许您想重定向标准错误以抑制错误消息？然后你可以简单地使用
wc -l Files/Unused-CMA_host.txt 2> /dev/null | awk '{print }'
In the case of a non-existent file, awkwill simply read from an empty stream and do nothing.
在文件不存在的情况下，awk将简单地从空流中读取并且什么都不做。
