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Less (Unix)
less is a terminal pager program on Unix, Windows, and Unix-like systems used to view (but not change) the contents of a text file one screen at a time. It is similar to , but has the extended capability of allowing both forward and backward navigation through the file. Unlike most Unix text editors/viewers, does not need to read the entire file before starting, allowing for immediate viewing regardless of file size. History Mark Nudelman initially wrote less during 1983–85, in the need of a version of more able to do backward scrolling of the displayed text. The name came from the joke of doing "backwards more." Originally, less was developed for Unix, but it has been ported to a number of other operating systems, including MS-DOS, Microsoft Windows, OS/2, and OS-9, as well as Unix-like systems such as Linux. It is still maintained today by Nudelman. To help remember the difference between less and more, a common joke is to say, "," implying that less has greater functiona ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Xterm
In computing, xterm is the standard terminal emulator for the X Window System. It allows users to run programs which require a command-line interface. If no particular program is specified, xterm runs the user's shell. An X display can show one or more user's xterm windows output at the same time. Each xterm window is a separate process, but all share the same keyboard, taking turns as each xterm process acquires ''focus''. Normally focus switches between X applications as the user moves the pointer (e.g., a mouse cursor) about the screen, but xterm provides options to ''grab focus'' (the ''Secure Keyboard'' feature) as well as accept input events sent without using the keyboard (the ''Allow SendEvents'' feature). Those options have limitations, as discussed in the xterm manual. xterm originated prior to the X Window System. It was originally written as a stand-alone terminal emulator for the VAXStation 100 (VS100) by Mark Vandevoorde, a student of Jim Gettys, in the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
MS-DOS
MS-DOS ( ; acronym for Microsoft Disk Operating System, also known as Microsoft DOS) is an operating system for x86-based personal computers mostly developed by Microsoft. Collectively, MS-DOS, its rebranding as IBM PC DOS, and a few operating systems attempting to be compatible with MS-DOS, are sometimes referred to as "DOS" (which is also the generic acronym for disk operating system). MS-DOS was the main operating system for IBM PC compatibles during the 1980s, from which point it was gradually superseded by operating systems offering a graphical user interface (GUI), in various generations of the graphical Microsoft Windows operating system. IBM licensed and re-released it in 1981 as PC DOS 1.0 for use in its PCs. Although MS-DOS and PC DOS were initially developed in parallel by Microsoft and IBM, the two products diverged after twelve years, in 1993, with recognizable differences in compatibility, syntax, and capabilities. Beginning in 1988 with DR-DO ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Grep
grep is a command-line utility for searching plain-text data sets for lines that match a regular expression. Its name comes from the ed command ''g/re/p'' (''globally search for a regular expression and print matching lines''), which has the same effect. grep was originally developed for the Unix operating system, but later available for all Unix-like systems and some others such as OS-9. History Before it was named, grep was a private utility written by Ken Thompson to search files for certain patterns. Doug McIlroy, unaware of its existence, asked Thompson to write such a program. Responding that he would think about such a utility overnight, Thompson actually corrected bugs and made improvements for about an hour on his own program called s (short for "search"). The next day he presented the program to McIlroy, who said it was exactly what he wanted. Thompson's account may explain the belief that grep was written overnight. Thompson wrote the first version in PDP-11 assem ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Regular Expression
A regular expression (shortened as regex or regexp; sometimes referred to as rational expression) is a sequence of characters that specifies a search pattern in text. Usually such patterns are used by string-searching algorithms for "find" or "find and replace" operations on strings, or for input validation. Regular expression techniques are developed in theoretical computer science and formal language theory. The concept of regular expressions began in the 1950s, when the American mathematician Stephen Cole Kleene formalized the concept of a regular language. They came into common use with Unix text-processing utilities. Different syntaxes for writing regular expressions have existed since the 1980s, one being the POSIX standard and another, widely used, being the Perl syntax. Regular expressions are used in search engines, in search and replace dialogs of word processors and text editors, in text processing utilities such as sed and AWK, and in lexical analysis. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Source Code
In computing, source code, or simply code, is any collection of code, with or without comments, written using a human-readable programming language, usually as plain text. The source code of a program is specially designed to facilitate the work of computer programmers, who specify the actions to be performed by a computer mostly by writing source code. The source code is often transformed by an assembler or compiler into binary machine code that can be executed by the computer. The machine code is then available for execution at a later time. Most application software is distributed in a form that includes only executable files. If the source code were included it would be useful to a user, programmer or a system administrator, any of whom might wish to study or modify the program. Alternatively, depending on the technology being used, source code may be interpreted and executed directly. Definitions Richard Stallman's definition, formulated in his 1989 seminal ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Syntax
In linguistics, syntax () is the study of how words and morphemes combine to form larger units such as phrases and sentences. Central concerns of syntax include word order, grammatical relations, hierarchical sentence structure ( constituency), agreement, the nature of crosslinguistic variation, and the relationship between form and meaning (semantics). There are numerous approaches to syntax that differ in their central assumptions and goals. Etymology The word ''syntax'' comes from Ancient Greek roots: "coordination", which consists of ''syn'', "together", and ''táxis'', "ordering". Topics The field of syntax contains a number of various topics that a syntactic theory is often designed to handle. The relation between the topics is treated differently in different theories, and some of them may not be considered to be distinct but instead to be derived from one another (i.e. word order can be seen as the result of movement rules derived from grammatical relations). ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Compressed Archive
In computing, an archive file is a computer file that is composed of one or more files along with metadata. Archive files are used to collect multiple data files together into a single file for easier portability and storage, or simply to compress files to use less storage space. Archive files often store directory structures, error detection and correction information, arbitrary comments, and sometimes use built-in encryption. Applications Portability Archive files are particularly useful in that they store file system data and metadata within the contents of a particular file, and thus can be stored on systems or sent over channels that do not support the file system in question, only file contents – examples include sending a directory structure over email, files with names unsupported on the target file system due to length or characters, and retaining files' date and time information. Additionally, it facilitates transferring high numbers of small files such as reso ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cat (Unix)
cat is a standard Unix utility that reads files sequentially, writing them to standard output. The name is derived from its function to (con)catenate files (from Latin ''catenare'', "to chain"). It has been ported to a number of operating systems. History cat was part of the early versions of Unix, e.g., Version 1, and replaced pr, a PDP-7 and Multics utility for copying a single file to the screen. It was written by Ken Thompson and Dennis Ritchie. The version of cat bundled in GNU coreutils was written by Torbjorn Granlund and Richard Stallman. The ReactOS version was written by David Welch, Semyon Novikov, and Hermès Bélusca. Over time, alternative utilities such as tac and bat also became available, bringing different new features. Usage The Single Unix Specification defines the operation of cat to read files in the sequence given in its arguments, writing their contents to the standard output in the same sequence. The specification mandates the support of one option ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Computer Terminal
A computer terminal is an electronic or electromechanical hardware device that can be used for entering data into, and transcribing data from, a computer or a computing system. The teletype was an example of an early-day hard-copy terminal and predated the use of a computer screen by decades. Early terminals were inexpensive devices but very slow compared to punched cards or paper tape for input, yet as the technology improved and video displays were introduced, terminals pushed these older forms of interaction from the industry. A related development was time-sharing systems, which evolved in parallel and made up for any inefficiencies in the user's typing ability with the ability to support multiple users on the same machine, each at their own terminal or terminals. The function of a terminal is typically confined to transcription and input of data; a device with significant local, programmable data-processing capability may be called a "smart terminal" or fat client. A t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Pipeline (Unix)
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. The second process is started as the first process is still executing, and they are executed concurrently. The concept of pipelines was championed by Douglas McIlroy at Unix's ancestral home of Bell Labs, during the development of Unix, shaping its toolbox philosophy. It is named by analogy to a physical pipeline. A key feature of these pipelines is their "hiding of internals" (Ritchie & Thompson, 1974). This in turn allows for more clarity and simplicity in the system. This article is about anonymous pipes, where data written by one process is buffered by the operating system until it is read by the next process, and this uni-directional channel disappears when the proc ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Standard Input
In computer programming, standard streams are interconnected input and output communication channels between a computer program and its environment when it begins execution. The three input/output (I/O) connections are called standard input (stdin), standard output (stdout) and standard error (stderr). Originally I/O happened via a physically connected system console (input via keyboard, output via monitor), but standard streams abstract this. When a command is executed via an interactive shell, the streams are typically connected to the text terminal on which the shell is running, but can be changed with redirection or a pipeline. More generally, a child process inherits the standard streams of its parent process. Application Users generally know standard streams as input and output channels that handle data coming from an input device, or that write data from the application. The data may be text with any encoding, or binary data. In many modern systems, the standard error st ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Standard Output
In computer programming, standard streams are interconnected input and output communication channels between a computer program and its environment when it begins execution. The three input/output (I/O) connections are called standard input (stdin), standard output (stdout) and standard error (stderr). Originally I/O happened via a physically connected system console (input via keyboard, output via monitor), but standard streams abstract this. When a command is executed via an interactive shell, the streams are typically connected to the text terminal on which the shell is running, but can be changed with redirection or a pipeline. More generally, a child process inherits the standard streams of its parent process. Application Users generally know standard streams as input and output channels that handle data coming from an input device, or that write data from the application. The data may be text with any encoding, or binary data. In many modern systems, the standard erro ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
