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When do you need to use process substitution?
Piping the stdout of a command into the stdin of another is a powerful technique. But, what if you need to pipe the stdout of multiple commands? This is where process substitution comes in. Process substitution feeds the output of a process (or processes) into the stdin of another process.
How can I use process substitution in Bash?
On systems lacking /dev/fd/ files, Bash may use temporary files. (Thanks, S.C.) Process substitution can compare the output of two different commands, or even the output of different options to the same command. Process substitution can compare the contents of two directories — to see which filenames are in one, but not the other.
How does process substitution work in Windows 10?
Process substitution feeds the output of a process (or processes) into the stdin of another process. Process substitution uses /dev/fd/ files to send the results of the process (es) within parentheses to another process.
How to use process substitution to compare two files?
Process substitution can compare the output of two different commands, or even the output of different options to the same command. Process substitution can compare the contents of two directories — to see which filenames are in one, but not the other. diff < (ls $first_directory) < (ls $second_directory)
Which is an example of process substitution in Bash?
Process substitution can also be used to capture output that would normally go to a file, and redirect it to the input of a process. The Bash syntax for writing to a process is >(command). Here is an example using the tee, wc and gzip commands that counts the lines in a file with wc -l and compresses it with gzip in one pass:
How is process substitution used to compare two programs?
Process substitution allows one to compare the output of two programs directly: The < (command) expression tells the command interpreter to run command and make its output appear as a file. The command can be any arbitrarily complex shell command.
How does process substitution work in JavaScript?
Process substitution allows a process’s input or output to be referred to using a filename. The process list is run asynchronously, and its input or output appears as a filename. This filename is passed as an argument to the current command as the result of the expansion.
Is it possible to use process substitution in FIFOs?
Process substitution is supported on systems that support named pipes (FIFOs) or the /dev/fd method of naming open files. It takes the form of Template – command list enclosed within parentheses:
What’s the difference between process substitution and redirection?
Note: