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The rule is that any redirection sets the handle to the output stream independently. So " 2>&1 " sets handle 2 to whatever handle 1 points to, which at that point usually is stdout . Then " > " redirects handle 1 to something else, e.g. a file, but it does not change handle 2 , which still points to stdout .
The Linux tee command was written by Mike Parker, Richard Stallman, and David MacKenzie. [5] The command is available as a separate package for Microsoft Windows as part of the UnxUtils collection of native Win32 ports of common GNU Unix-like utilities. [6] The FreeDOS version was developed by Jim Hall and is licensed under the GPL. [7]
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. For example, the dir and ls programs (which display file names contained in a directory) may take command-line arguments, but perform their operations without any stream ...
Since version 2.05b Bash can redirect standard input (stdin) from a "here string" using the <<< operator. Bash 3.0 supports in-process regular expression matching using a syntax reminiscent of Perl. [96] In February 2009, [97] Bash 4.0 introduced support for associative arrays. [4] Associative array indices are strings, in a manner similar to ...
It is often abbreviated as NUL (or NULL, though in some contexts that term is used for the null pointer). In 8-bit codes, it is known as a null byte . The original meaning of this character was like NOP —when sent to a printer or a terminal , it has no effect (some terminals, however, incorrectly display it as space ).
Alternatively, if the drain does not need to read any input from stdin to do something useful, it can be given < /dev/null as input. As all components of a pipe are run in parallel, a shell typically forks a subprocess (a subshell) to handle its contents, making it impossible to propagate variable changes to the outside shell environment.
Input from a terminal never really "ends" (unless the device is disconnected), but it is useful to enter more than one "file" into a terminal, so a key sequence is reserved to indicate end of input.
To perform input/output on a stream, one either uses the read and write system calls as with regular file descriptors, or a set of STREAMS-specific functions to send control messages. [ 19 ] Ritchie admitted to regretting having to implement Streams in the kernel, rather than as processes, but felt compelled to do so for reasons of efficiency ...