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Mohamed Yahia
Mohamed Yahia

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piping in unix-like systems


  • redirection

Piping is a very useful feature in bash. You can connect the standard output of a command to be the standard input of another command.

The first type of pipe is like this. A one to one pipe. stdout of 1st command goes as stdin of the 2nd command.

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ls -hl | wc -l

The pipe character or operator is the | character. In the previous command, we long listed ls -l the contents of the current working directory in a human readable format -h. Then, we passed the output of that command (instead of getting printed to the terminal) as an input or standard input (stdin) to the second command wc and -l option counts the lines of the list only. So the output of the whole command ls -hl | wc -l is the number of objects (files, directories, etc) located in the current working directory (cwd).

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The second way to pipe commands is like this. That way you can redirect the output of the 1st command to a file and to a 2nd command.

ls -hl | tee output.txt | wc -l

The tee command is what allows us to do this. It takes the stdout of the first command saves the output to a file and passes it to the wc command.

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