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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).
Example usage of tee: The output of ls -l is redirected to tee which copies them to the file file.txt and to the pager less. The name tee comes from this scheme - it looks like the capital letter T The tee command is normally used to split the output of a program so that it can be both displayed and saved in a file.
After the release of Version 10, the Unix research team at Bell Labs turned its focus to Plan 9 from Bell Labs, a distinct operating system that was first released to the public in 1993. All versions of BSD from its inception up to 4.3BSD-Reno are based on Research Unix, with versions starting with 4.4 BSD and Net/2 instead becoming Unix-like.
rc (for "run commands") is the command line interpreter for Version 10 Unix and Plan 9 from Bell Labs operating systems. It resembles the Bourne shell , but its syntax is somewhat simpler. It was created by Tom Duff , who is better known for an unusual C programming language construct (" Duff's device ").
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 CSRG incorporated the r-commands into their Unix operating system, the Berkeley Software Distribution (BSD). The r-commands premiered in BSD v4.1. [2] Among the programs in the suite are: rcp (remote copy), rexec (remote execution), rlogin (remote login), rsh (remote shell), rstat, ruptime, and rwho (remote who). [2] [3]
The original Unix file system supported three types of files: ordinary files, directories, and "special files", also termed device files. [1] The Berkeley Software Distribution (BSD) and System V each added a file type to be used for interprocess communication: BSD added sockets, [3] while System V added FIFO files.
Xpdf runs on nearly any Unix-like operating system.Binaries are also available for Windows.Xpdf can decode LZW and read encrypted PDFs. The official version obeys the DRM restrictions of PDF files, [7] which can prevent copying, printing, or converting some PDF files. [4]