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: duplicate an open file descriptor – System Interfaces Reference, The Single UNIX Specification, Version 4 from The Open Group; Redirection Definition by The Linux Information Project (LINFO) I/O Redirection in The Linux Documentation Project; Redirection in Windows; Creating a Child Process with Redirected Input and Output in Windows
/A Append the pipeline content to the output file(s) rather than overwriting them. Note: When tee is used with a pipe, the output of the previous command is written to a temporary file. When that command finishes, tee reads the temporary file, displays the output, and writes it to the file(s) given as command-line argument.
Another Unix breakthrough was to automatically associate input and output to terminal keyboard and terminal display, respectively, by default [citation needed] — the program (and programmer) did absolutely nothing to establish input and output for a typical input-process-output program (unless it chose a different paradigm).
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:
The > in the third example is a redirection operator, telling the command-line interpreter to send the output of the command not to its own standard output (the screen) but to the named file. This will overwrite the file. Using >> will redirect the output and append it to the file.
In the calling process the lowest numbered unused file descriptor will be used for the new file descriptor number. When using the dup2() system call it performs the same task as dup() with the exception of using the file descriptor number specified in the newfd variable of the call, in that newfd is adjusted to refer to the oldfd file description.
$ # bash shell $ /bin/bash-c 'echo a{p,c,d,b}e' ape ace ade abe $ # A traditional shell does not produce the same output $ /bin/sh-c 'echo a{p,c,d,b}e' a{p,c,d,b}e When brace expansion is combined with wildcards, the braces are expanded first, and then the resulting wildcards are substituted normally.
Command Prompt, a CLI shell in Windows Bash, a widely adopted Unix shell. A command-line interface (CLI) is an operating system shell that uses alphanumeric characters typed on a keyboard to provide instructions and data to the operating system, interactively.