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It was created by Tom Duff, who is better known for an unusual C programming language construct ("Duff's device"). [1] A port of the original rc to Unix is part of Plan 9 from User Space. A rewrite of rc for Unix-like operating systems by Byron Rakitzis is also available but includes some incompatible changes.
If-then-else flow diagram A nested if–then–else flow diagram. In computer science, conditionals (that is, conditional statements, conditional expressions and conditional constructs) are programming language constructs that perform different computations or actions or return different values depending on the value of a Boolean expression, called a condition.
The C shell implements both shell and environment variables. [14] Environment variables, created using the setenv statement, are always simple strings, passed to any child processes, which retrieve these variables via the envp[] argument to main(). Shell variables, created using the set or @ statements, are internal to C shell. They are not ...
In such case it is always possible to use a function call, but this can be cumbersome and inelegant. For example, to pass conditionally different values as an argument for a constructor of a field or a base class, it is impossible to use a plain if-else statement; in this case we can use a conditional assignment expression, or a function call ...
The null command may take parameters, which are ignored. It is also used as a no-op dummy command for side-effects such as assigning default values to shell variables through the ${parameter:=word} parameter expansion form. [2] For example, from bashbug, the bug-reporting script for Bash: : $
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 shell scripts .
In Unix shell scripting and in utilities such as Makefiles, the "$" is a unary operator that translates the name of a variable into its contents. While this may seem similar to a sigil, it is properly a unary operator for lexical indirection , similar to the * dereference operator for pointers in C , as noticeable from the fact that the dollar ...
A shell script is a computer program designed to be run by a Unix shell, a command-line interpreter. [1] The various dialects of shell scripts are considered to be command languages . Typical operations performed by shell scripts include file manipulation, program execution, and printing text.