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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).
Unix shells use dup2 for input/output redirection. Along with pipe(), it is a tool on which Unix pipes rely. The following example uses pipe() and dup() in order to connect two separate processes (program1 and program2) using Unix pipes:
This class of status code indicates the client must take additional action to complete the request. Many of these status codes are used in URL redirection. [2] A user agent may carry out the additional action with no user interaction only if the method used in the second request is GET or HEAD. A user agent may automatically redirect a request.
They are a limited form of inter-process communication (IPC), typically used in Unix, Unix-like, and other POSIX-compliant operating systems. A signal is an asynchronous notification sent to a process or to a specific thread within the same process to notify it of an event.
In Unix-like computer operating systems, a pipeline is a mechanism for inter-process communication using message passing. A pipeline is a set of processes chained together by their standard streams , so that the output text of each process ( stdout ) is passed directly as input ( stdin ) to the next one.
In computing, the exit status (also exit code or exit value) of a terminated process is an integer number that is made available to its parent process (or caller). In DOS , this may be referred to as an errorlevel .
Version 5 AT&T UNIX test: Shell programming Mandatory Evaluate expression: Version 7 AT&T UNIX time: Process management Mandatory Retrieve and format time and date Version 3 AT&T UNIX timeout: Process management Mandatory Run command with a time limit Version 3 AT&T UNIX touch: Filesystem Mandatory Change file access and modification times
Request codes are often device-specific. For instance, a CD-ROM device driver which can instruct a physical device to eject a disc would provide an ioctl request code to do so. Device-independent request codes are sometimes used to give userspace access to kernel functions which are only used by core system software or still under development.