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Moha the almighty camel
Asked: 2014-11-03 00:54:07 +0800 CST

why is piping pgrep output into kill is not working

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I am playing around with pipes to learn how to use them. I am trying this command to kill a process by name: pgrep <some_process> | kill

but the output I am getting is the usage instruction for kill, like it didn't receive any input.

of course I know there are easier way to accomplish the same task like pkill or killall, but I want to know why is this not working.

Thank you

command-line

3 Answers

  1. Best Answer

    kill is not reading anything from stdin but expects some command line args and throws an error if it doesn't get them.

    Piping only works if the program on the right side of the pipe is actually reading from the pipe. Not all programs do.

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  2. As Florian explained, kill expects command line inputs.

    To go around the problem you can use

    • xargs to build command line arguments for a command, e.g., pgrep vivaldi | xargs kill or better yet pgrep vivaldi | awk 'BEGIN{ORS=" "} 1' | xargs kill
    • shell's substitution: kill $(pgrep vivaldi)
    • killall which does pretty much the same job as pgrep and kill combined , e.g., killall vivaldi
    • pkill , another utility to kill based on name, e.g., pkill vivaldi
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  3. For killing a program by its name, if you actually know the process' name, you could just use the command skill <your process name>;

    Now for pipes, a good way to understand them is playing around with tools like echo, more, less, tail, head, etc. There are many programs that can actually read from a pipe... one I have always used is grep.

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