Command language in the context of Web query

In computer science, human–computer interaction, and interaction design, direct manipulation is an approach to interfaces which involves continuous representation of objects of interest together with rapid, reversible, and incremental actions and feedback. As opposed to other interaction styles, for example, the command language, the intention of direct manipulation is to allow a user to manipulate objects presented to them, using actions that correspond at least loosely to manipulation of physical objects. An example of direct manipulation is resizing a graphical shape, such as a rectangle, by dragging its corners or edges with a mouse.

Having real-world metaphors for objects and actions can make it easier for a user to learn and use an interface (some might say that the interface is more natural or intuitive), and rapid, incremental feedback allows a user to make fewer errors and complete tasks in less time, because they can see the results of an action before completing the action, thus evaluating the output and compensating for mistakes.

A "Unix shell" is a shell that provides a command-line user interface for a Unix-like operating system. A Unix shell provides a command language that can be used either interactively or for writing a shell script. A user typically works within a Unix shell via a terminal emulator; however, direct access via serial hardware connections or a Secure Shell are common for server systems. Although use of a Unix shell is popular with some users, others prefer to use a graphical shell in a windowing system, such as those provided in desktop Linux distributions or macOS, instead of a command-line interface (CLI).

A user may have access to multiple Unix shells with one configured to run by default when the user logs in interactively. The default selection is typically stored in a user's profile (for example, in the local passwd file or in a distributed configuration system such as NIS or LDAP). A user may use other shells nested inside the default shell.

A computer language is a formal language for humans to communicate with a computer, not a natural language. In earlier days of computing (before the 1980s), the term was used interchangeably with programming language, but today, used primarily for taxonomy, is a broader term that encompasses languages that are not programming in nature. Sub-categories (with possibly contended hierarchical relationships) include:

• Construction
  • Programming – for controlling computer behavior
    • Command – for controlling the tasks of a computer, such as starting programs
    • Query – for querying databases and information systems
    • Transformation – for transforming the text of a formal language into text that meets a specific goal
  • Structural
    • Configuration – for writing configuration files
    • Data exchange – examples: JSON, XML
    • Markup – for annotating a document in a way that is syntactically distinguishable from the text, such as HTML
    • Page description – for describing the appearance of a printed page in a higher level than an actual output bitmap
    • Style sheet – for expressing the presentation of structured documents, such as CSS
• Modeling – for designing systems
  • Architecture description – for describing and representing system architecture
  • Hardware description – for modeling integrated circuits
• Simulation – for simulating
• Specification – for describing what a system should do