A direction line interface or order dialect translator (CLI), otherwise called direction line UI, support client interface[1] and character UI (CUI), is a methods for connecting with a PC program where the client (or customer) issues directions to the program as progressive lines of content (order lines). A program which handles the interface is known as an order dialect translator or shell (figuring).

The CLI was the essential methods for communication with most PC frameworks on work stations in the mid-1960s, and kept on being utilized all through the 1980s on OpenVMS, Unix frameworks and PC frameworks including MS-DOS, CP/M and Apple DOS. The interface is normally executed with a direction line shell, or, in other words that acknowledges directions as content information and changes over directions into proper working framework capacities.

Today, many end clients infrequently, if at any point, utilize direction line interfaces and rather depend upon graphical UIs and menu-driven collaborations. In any case, numerous product designers, framework overseers and propelled clients still depend vigorously on direction line interfaces to perform undertakings all the more effectively, arrange their machine, or access projects and program includes that are not accessible through a graphical interface.

Options in contrast to the direction line incorporate, yet are not constrained to content UI menus (see IBM AIX SMIT for instance), console easy routes, and different other work area similitudes focused on the pointer (typically controlled with a mouse). Precedents of this incorporate the Windows forms 1, 2, 3, 3.1, and 3.11 (an OS shell that keeps running in DOS), DosShell, and Mouse Systems PowerPanel.

Projects with order line interfaces are by and large less demanding to computerize through scripting.

Order line interfaces for programming other than working frameworks incorporate various programming dialects, for example, Tcl/Tk, PHP, and others, and in addition utilities, for example, the pressure utility WinZip, and some FTP and SSH/Telnet customers.

Contrasted and a graphical UI, a direction line requires less framework assets to actualize. Since alternatives to directions are given in a couple of characters in each order line, an accomplished client finds the choices less demanding to get to. Mechanization of dull assignments is disentangled - most working frameworks utilizing an order line interface bolster some system for putting away as often as possible utilized arrangements in a circle record, for re-utilize; this may reach out to a scripting dialect that can take parameters and variable alternatives. A direction line history can be continued, permitting audit or redundancy of directions.

An order line framework may require paper or online manuals for the client's reference, albeit frequently a "help" choice gives a compact audit of the choices of a direction. The order line condition may not give the graphical improvements, for example, extraordinary text styles or broadened alter windows found in a GUI. It might be troublesome for another client to get comfortable with every one of the directions and alternatives accessible, contrasted and the drop-down menus of a graphical UI, without rehashed reference to manuals.

Working framework (OS) order line interfaces are typically particular projects provided with the working framework. A program that actualizes such a content interface is regularly called a direction line translator, order processor or shell.

Models of direction line mediators incorporate DEC's DIGITAL Command Language (DCL) in OpenVMS and RSX-11, the different Unix shells (sh, ksh, csh, tcsh, bash, and so forth.), CP/M's CCP, DOS's COMMAND.COM, and in addition the OS/2 and the Windows CMD.EXE programs, the last gatherings being founded intensely on DEC's RSX-11 and RSTS CLIs. Under most working frameworks, it is conceivable to supplant the default shell program with options; models incorporate 4DOS for DOS, 4OS2 for OS/2, and 4NT or Take Command for Windows.

In spite of the fact that the term 'shell' is regularly used to depict a direction line mediator, entirely talking a 'shell' can be any program that comprises the UI, including completely graphically situated ones. For instance, the default Windows GUI is a shell program named EXPLORER.EXE, as characterized in the SHELL=EXPLORER.EXE line in the WIN.INI arrangement document. These projects are shells, however not CLIs.