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In computing, redirection is a form of interprocess communication, and is a function common to most command-line interpreters, including the various Unix shells that can redirect standard streams to user-specified locations. The concept of redirection is quite old, dating back to the earliest operating systems (OS).
The standard shell syntax for anonymous pipes is to list multiple commands, separated by vertical bars ("pipes" in common Unix verbiage): command1 | command2 | command3 For example, to list files in the current directory ( ls ), retain only the lines of ls output containing the string "key" ( grep ), and view the result in a scrolling page ...
Standard input is a stream from which a program reads its input data. The program requests data transfers by use of the read operation. Not all programs require stream input.
These commands can be found on Unix operating systems and most Unix-like operating systems. This is not a comprehensive list of all utilities that existed in the various historic Unix and Unix-like systems, as it excludes utilities that were not mandated by the aforementioned standard.
Unix shells use dup2 for input/output redirection. Along with pipe(), it is a tool on which Unix pipes rely. The following example uses pipe() and dup() in order to connect two separate processes (program1 and program2) using Unix pipes:
In Unix-like operating systems, true and false are commands whose only function is to always return with a predetermined exit status.Programmers and scripts often use the exit status of a command to assess success (exit status zero) or failure (non-zero) of the command.
This is a list of commands from the GNU Core Utilities for Unix environments. These commands can be found on Unix operating systems and most Unix-like operating systems. GNU Core Utilities include basic file, shell and text manipulation utilities. Coreutils includes all of the basic command-line tools that are expected in a POSIX system.
Common Unix filter programs are: cat, cut, grep, head, sort, tail, and uniq. Programs like awk and sed can be used to build quite complex filters because they are fully programmable. Unix filters can also be used by Data scientists to get a quick overview about a file based dataset. [2]