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8.4.3. Predefined Shell Variables
Last revision August 6, 2004 Expressions can be used in assigning values to new variables; as substitutions in command lines in the script; and in flow-of-control statements : if , foreach , while , and switch .
A pipeline of three programs run on a text terminal
Redirection is the transferring of standard output to some other destination, such as another program, a file or a printer, instead of the display monitor (which is its default destination). Standard output, sometimes abbreviated stdout , is the destination of the output from command line (i.e., all-text mode) programs in Unix-like operating systems.
A shell is software that provides an interface for users of an operating system to access the services of a kernel .
tcsh and sh shell windows on a Mac OS X desktop.
The C shell ( csh or the improved version, tcsh , on most machines) is a Unix shell that was created by Bill Joy while a graduate student at University of California, Berkeley in the late 1970s. It has been distributed widely, beginning with the 2BSD release of the BSD Unix system that Joy began distributing in 1978. [ 2 ] [ 3 ] Other early contributors to the ideas or the code were Michael Ubell, Eric Allman , Mike O'Brien and Jim Kulp. [ 4 ]
A here document (also called a here-document , a heredoc , a hereis , a here-string or a here-script ) is a way of specifying a string literal in command line shells including Unix shells ( sh , csh , ksh , Bash and zsh ) and in programming or scripting languages such as Perl , PHP , Python , PowerShell and Ruby . It preserves the line breaks and other whitespace (including indentation) in the text. Some languages allow variable substitution and command substitution inside the string.
The foreach line loops through all entries in the paren list, setting the variable l to each one and then executing the loop body.
This is a collection of useful one-line csh-commands and short multi-line contructs, intended to give some practical hints to both novice and veteran csh and sh users.
tcsh ( pronunciation: / ˌ t iː ˈ s iː ʃ ɛ l / "tee-cee-shell", / ˈ t iː ʃ ɛ l / "tee-shell", or as an acronym "tee cee ess aitch") is a Unix shell based on and compatible with the C shell (csh).
One of the fundamental features that makes Linux and other Unices useful is the “pipe”. Pipes allow separate processes to communicate without having been designed explicitly to work together.