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tory in order for instance to make the prompt more informative or visually pleasing to distinguish sessions on various machines or to indicate the current level of nesting of commands on some systems special tokens in the definition of the prompt can be used to cause external programs to be called by the command line interpreter while displaying the prompt in dos command com and in windows nt s cmd exe users can modify the prompt by issuing a prompt command or by directly changing the value of the corresponding prompt environment variable the default of most modern systems the c style is obtained for instance with prompt p g the default of older dos systems c is obtained by just prompt although on some systems this produces the newer c style unless used on floppy drives a or b on those systems prompt n g can be used to override the automatic default and explicitly switch to the older style many unix systems feature the ps1 variable prompt string 1 24 although other variables also may affect the prompt depending on the shell used in the bash shell a prompt of the form time user host work_dir could be set by issuing the command export ps1 t u h w in zsh the rprompt variable controls an optional prompt on the right hand side of the display it is not a real prompt in that the location of text entry does not change it is used to display information on the same line as the prompt but right justified in risc os the command prompt is a symbol and thus os cli commands are often referred to as star commands 25 one can also access the same commands from other command lines such as the bbc basic command line by preceding the command with a in ibm s tso the command prompt is referred to as the ready prompt after the word ready in the prompt example of prompt system displays all the information that can be displayed by the liquidprompt command prompt system here using its jolly theme liquidprompt display example using its default theme liquidprompt display example using its pureship theme liquidprompt display example using its powerline theme some shells such as bash zsh and powershell allow the use of prompt systems that display a lot more information in the command prompt like the type of remote connection the state of machine sensors or additional information about a version control system they often use several ansi colors unicode characters and advanced shell features to set up a colorful display arguments edit this article needs more citations please help improve this article by adding citations to reliable sources unsourced material may be challenged and removed find sources command line interface news newspapers books scholar jstor june 2026 learn how and when to remove this message an ms dos command line illustrating parsing into command and arguments a command line argument or parameter is an item of information provided to a program when it is started 26 a program can have many command line arguments that identify sources or destinations of information or that alter the operation of the program when a command processor is active a program is typically invoked by typing its name followed by command line arguments if any for example in unix and unix like environments an example of a command line argument is rm file s file s is a command line argument which tells the program rm to remove the file named file s some programming languages such as c c and java allow a program to interpret the command line arguments by handling them as string parameters in the main function 27 28 other languages such as python expose operating system specific api functionality through the sys module 29 and in particular sys argv for command line arguments in unix like operating systems a single hyphen used in place of a file name is a special value specifying that a program should handle data coming from the standard input or send data to the standard output command line option edit a command line option or simply option also known as a flag or switch modifies the operation of a command the effect is determined by the command s program options follow the command name on the command line separated by e g commas or spaces separators are not always required such as dir and dir in dos which have the same effect 23 of listing the dir command s available options whereas dir help in many versions of unix does require the option to be preceded by at least one space and is case sensitive the format of options varies widely between operating systems in most cases the syntax is by convention rather than an operating system requirement the entire command line is simply a string passed to a program which can process it in any way the programmer wants so long as the interpreter can tell where the command name ends and its arguments and options begin a few representative samples of command line options most relating to listing files in a directory to illustrate some conventions operating system command valid alternative notes openvms directory owner dir owner instruct the directory command to also display the ownership of the files note the directory command name is not case sensitive and can be abbreviated to as few letters as required to remain unique windows dir q o s d dir q d o s display ownership of files whose names begin with d or d sorted by size smallest first note spaces around argument d are required unix like systems ls ls d ls s l d display in long format files and directories whose names begin with d but not d sorted by size largest first note spaces are required around all arguments and options but some can be run together e g ls is the same as l s data general rdos cli list e s 04 26 80 b list s e 4 26 80 b list every attribute for files created before 26 april 1980 note the b at the end of the date argument is a local switch that modifies the meaning of that argument while s and e are global switches i e apply to the whole command vm cms cli listfile fulldate l ful includes the date the file was last written in the list note the listfile command name is not case sensitive and can be abbreviated to as few letters as required to remain unique os 360 operator commands start taperdr dsname foo bar s taperdr dsn foo bar start the procedure named taperdr with the supplied data set name tso listcat level foo members listc l foo m list datasets at specified index level and list members for each pds send text user foo se text u foo send message to specified user command line argument parsing is used to parse the arguments of a program and such functionality is offered in various languages for example getopt is in the c posix library for parsing arguments abbreviating commands edit see also tab completion in multics command line options and subsystem keywords may be abbreviated this idea appears to derive from the pl i programming language with its shortened keywords e g strg for stringrange and dcl for declare for example in the multics forum subsystem the long_subject parameter can be abbreviated lgsj it is also common for multics commands to be abbreviated typically corresponding to the initial letters of the words that are strung together with underscores to form command names such as the use of did for delete_iacl_dir in some other systems abbreviations are automatic such as permitting enough of the first characters of a command name to uniquely identify it such as su as an abbreviation for superuser while others may have some specific abbreviations pre programmed e g md for mkdir in command com or user defined via batch scripts and aliases e g alias md mkdir in tcsh option conventions in dos windows os 2 edit on dos os 2 and windows different programs called from their command com or cmd exe or internally their commands may use different syntax within the same operating system for example options may be indicated by either of the switch characters or either may be allowed see below they may or may not be case sensitive sometimes options and their arguments are run together sometimes separated by whitespace and sometimes by a character typically or thus prog ffilename prog f filename prog f filename prog f filename some programs allow single character options to be combined 23 others do not the switch fa may mean the same as f a 23 or it may be incorrect or it may even be a valid but different parameter in dos os 2 and windows the forward slash is most prevalent although the hyphen minus is also sometimes used in many versions of dos ms dos pc dos 2 xx and higher all versions of dr dos since 5 0 as well as pts dos embedded dos freedos and rxdos the switch character sometimes abbreviated switchar or switchchar to be used is defined by a value returned from a system call int 21h ax 3700h the default character returned by this api is but can be changed to a hyphen minus on the above mentioned systems except for under datalight rom dos and ms dos pc dos 5 0 and higher which always return from this call unless one of many available tsrs to reenable the switchar feature is loaded in some of these systems ms dos pc dos 2 xx dos plus 2 1 dr dos 7 02 and higher pts dos embedded dos freedos and rxdos the setting can also be pre configured by a switchar directive in config sys general software s embedded dos provides a switch command for the same purpose whereas 4dos allows the setting to be changed via setdos w n 30 under dr dos if the setting has been changed from the first directory separator in the display of the prompt parameter g will change to a forward slash which is also a valid directory separator in dos flexos 4680 os 4690 os os 2 and windows thereby serving as a visual clue to indicate the change 23 also the current setting is reflected also in the built in help screens 23 some versions of dr dos command com also support a prompt token to display the current setting command com since dr dos 7 02 also provides a pseudo environment variable named to allow portable batch jobs to be written 31 32 several external dr dos commands additionally support an environment variable switchar to override the system setting however many programs are hardwired to use only rather than retrieving the switch setting before parsing command line arguments a very small number mainly ports from unix like systems are programmed to accept even if the switch character is not set to it for example netstat and ping supplied with microsoft windows will accept the option to list available options and yet the list will specify the convention option conventions in unix like systems edit this section needs more citations please help improve this section by adding citations to reliable sources unsourced material may be challenged and removed july 2021 learn how and when to remove this message in unix like systems the ascii hyphen minus begins options the new and gnu convention is to use two hyphens then a word e g create to identify the option s use while the old convention and still available as an option for frequently used options is to use one hyphen then one letter e g c if one hyphen is followed by two or more letters it may mean two options are being specified or it may mean the second and subsequent letters are a parameter such as filename or date for the first option 33 two hyphen minus characters without following letters may indicate that the remaining arguments should not be treated as options which is useful for example if a file name itself begins with a hyphen or if further arguments are meant for an inner command e g sudo double hyphen minuses are also sometimes used to prefix long options where more descriptive option names are used this is a common feature of gnu software the getopt function and program and the getopts command are usually used for parsing command line options unix command names arguments and options are case sensitive except in a few examples mainly where popular commands from other operating systems have been ported to unix option conventions in other systems edit flexos 4680 os and 4690 os use cp m typically used conversational monitor system cms uses a single left parenthesis to separate options at the end of the command from the other arguments for example in the following command the options indicate that the target file should be replaced if it exists and the date and time of the source file should be retained on the copy copy source file a target file b replace olddate os 360 operator commands use a comma separated list of positional and keyword parameters only documented command and keyword abbreviations are valid keyword values are separated from the keywords with equal signs tso commands use a space separated list of positional and keyword parameters keywords may be truncated to any unique substring only documented command abbreviations are valid keyword values are inside parentheses data general s cli under their rdos aos etc operating systems as well as the version of cli that came with their business basic uses only as the switch character is case insensitive and allows local switches on some arguments to control the way they are interpreted such as mac u lib s a b c lpt l has the global option u to the macro assembler command to append user symbols but two local switches one to specify lib should be skipped on pass 2 and the other to direct listing to the printer lpt built in usage help edit see also help command one of the criticisms of a cli is the lack of cues to the user as to the available actions 34 in contrast guis usually inform the user of available actions with menus icons or other visual cues 35 to overcome this limitation many cli programs display a usage message typically when invoked with no arguments or one of h h h h help help or help 23 36 however entering a program name without parameters in the hope that it will display usage help can be hazardous as programs and scripts for which command line arguments are optional will execute without further notice although desirable at least for the help parameter programs may not support all option lead in characters exemplified above under dos where the default command line option character can be changed from to programs may query the switchar api in order to determine the current setting so if a program is not hardwired to support them all a user may need to know the current setting even to be able to reliably request help if the switchar has been changed to and therefore the character is accepted as an alternative path delimiter at the dos command line programs might misinterpret options like h or h as paths rather than help parameters 23 however if given as the first or only parameter most dos programs will by convention accept it as a request for help regardless of the current switchar setting 23 30 in some cases different levels of help can be selected for a program some programs supporting this allow giving a verbosity level as an optional argument to the help parameter as in h 1 h 2 etc or they give just a short help on help parameters with a question mark and...