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Each | tells the shell to connect the standard output of the command on the left to the standard input of the command on the right by an inter-process communication mechanism called an (anonymous) pipe, implemented in the operating system. Pipes are unidirectional; data flows through the pipeline from left to right.
A simplified but non-POSIX conforming form of the command, command > file 2 > & 1 is (not available in Bourne Shell prior to version 4, final release, or in the standard shell Debian Almquist shell used in Debian/Ubuntu): command & >file or command > & file. It is possible to use 2>&1 before ">" but the result is commonly misunderstood. The ...
Every pipe is placed in the root directory of the named pipe filesystem (NPFS), mounted under the special path \\.\pipe\ (that is, a pipe named "foo" would have a full path name of \\.\pipe\foo). Anonymous pipes used in pipelining are actually named pipes with a random name. They are very rarely seen by users, but there are notable exceptions.
tcsh and sh shell windows on a Mac OS X Leopard [1] desktop. A Unix shell is a command-line interpreter or shell that provides a command line user interface for Unix-like operating systems. The shell is both an interactive command language and a scripting language, and is used by the operating system to control the execution of the system using ...
Execute the substituted command in the background (sort file2 in this case), piping its output to the anonymous pipe. Execute the primary command, replacing the substituted command with the path of the anonymous pipe. In this case, the full command might expand to something like diff file1 /dev/fd/63.
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A metacharacter is a character that has a special meaning to a computer program, such as a shell interpreter or a regular expression (regex) engine.. In POSIX extended regular expressions, there are 14 metacharacters that must be escaped — preceded by a backslash (\) — in order to drop their special meaning and be treated literally inside an expression: opening and closing square brackets ...
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