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Designing command-line interfaces

• alexholehouse 15y ago
  Additionally, for interactive CLI programs or suites of programs, consistency is key. Offer the same way to select options, confirm or deny information, input data etc. I'm also working on a project where by entering "?" at any interactive section you're taken to an interactive help menu. From here you can query (amongst other things) the state of the program, something that isn't always clear when you're using command line software, as you can't have extra info somewhere in the corner or whatever.
• supersillyus 15y ago
  I'm glad he mentioned the "Silence trumps noise" point. I like to call the idiom "no news is good news". Tell me only when I need to know something (like a failure); "-v" is always there if I need it. It feels uncomfortable to get no output at first, but once you get used to it there's much less to read. It's rather like the Plan 9 convention of programs returning strings instead of ints when then terminate; an empty string means success, a non-empty string contains the error message. I wish other OSes had adopted that.
  • njharman 15y ago
    Problem with "silence" and "no news" is they are indistinguishable from many failure modes. I vastly prefer confirmation of action(s) as default and -q flag. At very lest there needs to be -v flag that provides confirmation of action(s)
    • joeyh 15y ago
      Configure your shell to report nonzero exit statuses. joey@gnu:~>true joey@gnu:~>false zsh: exit 1 In zsh this is done by "setopt print_exit_value". It's a pity shells don't do it by default.
      • njharman 15y ago
        Good hint, but it's value is very niche. Waiting until exit for status is fail. Many commands take seconds if not minutes/hours to complete. I wanna see some indication that they are working and not hung/etc.
  • BrandonM 15y ago
    There is no silence vs noise problem. Send output to STDOUT and "noise" to STDERR. Use -q and -v when appropriate. I thought it was weird that the author created a false dichotomy between being informational and giving only output that can be easily processed.
• mcantor 15y ago
  Here's another one: Provide explicit flags for default behavior. For example, if your lines-of-code counting utility excludes preprocessor directives by default, and includes them when you pass "-i", provide an "-x" switch that signals to use the default behavior. This way, when someone wants to write a bash script that uses your utility, they can do this: case $include_directives in y) LOC_FLAGS='-i';; n) LOC_FLAGS='-x';; esac myloc $LOC_FLAGS This has three benefits: 1.) It's explicit, and thus more obvious and clearer. 2.) It's more consistent, so there's no risk of empty/unset variables, whitespace, or other edge conditions screwing up a delicate munging operation. 3.) It's change-tolerant, so if future versions of your utility change the default behavior, scripts will continue functioning as expected.
  • a3_nm 15y ago
    Other benefit: if you aliased myownloc="myloc -i --complicated_option", you can run myownloc -x to selectively disable the -i switch.
  • reinhardt 15y ago
    What about the disadvantages? - It doubles the number of flags of the program. - It allows invalid or ambiguous combinations: is `myloc -i -x` valid? If yes which flag takes precedence? It seems these must outweigh the benefits or it wouldn't be so uncommon.
    • ams6110 15y ago
      I've seen two conventions for conflicting flags: complain and bail out, or "last one wins" so in your example, -x.
    • joeyh 15y ago
      Don't call it -i and -x, call it -i and --no-i or better, -i, --include and --no-include. Some getopts can provide this automatically. Last flag wins is a common choice because it allows some script to contain yourcommand --include $@ and then you can override with --no-include.
    • 15y ago
• FaceKicker 15y ago
  Non-interactive programs get the most attention in this article, while text-based user interfaces are barely covered at all. That's disappointing, I was hoping I'd learn how vi, etc. worked from this, since I know nothing about writing command line interfaces other than input and output to the last column of the last line of the terminal. Does anyone know of a good article/introduction to this?
  • antoarts 15y ago
    If you want to know how to create programs like vi, you should check out ncurses (http://www.gnu.org/s/ncurses/ http://www.gnu.org/s/ncurses/, tutorial: http://tldp.org/HOWTO/NCURSES-Programming-HOWTO/ http://tldp.org/HOWTO/NCURSES-Programming-HOWTO/)
  • a3_nm 15y ago
    Besides the technical details, there are good practices which should be followed, but I don't know of any document which lists them. This is a pity, because though text-based interfaces are often designed in a much more efficient way than GUI interfaces, they are seldom consistent between themselves, and often get something wrong. A few common ones: - Don't make the user reach for distant keys like escape or pagedown/pageup (also support ^N/^P or ^B/^F) or the arrow keys (also support hjkl), unless you really need to. - For one-line text entry, support readline bindings (^W, ^U, ^Y, ^B, ^F, etc.) - If you show a list, provide a way to search for an item rather than moving through the list item by item or page by page. - Unless there is a good reason not to, spawn $PAGER to show text and $EDITOR to edit text. - If there is a finite set of actions to choose from, provide one-key hotkeys for each one. Don't require unnecessary use of the control key. Optionally show the list of possible or common actions, but have an option to hide it and save screen space for users who don't need it anymore (like mutt does). Likewise, if there are several items that can get focus, provide hotkeys, don't require the user to Tab their way through all of them. Obviously, there are more.
    • technomancy 15y ago
      > For one-line text entry, support readline bindings (^W, ^U, ^Y, ^B, ^F, etc.) Better yet, don't try to emulate readline--just use readline itself. > spawn $PAGER to show text and $EDITOR to edit text. If you're old school enough, honor $VISUAL and fall back to $EDITOR if it's not set.
• huhtenberg 15y ago
  (edit) There is a bit of terminology substitution going on in linked article. Command line interface is a shell. That's where one types the commands. Calling command options and arguments an interface may be technically correct, but it is not what is conventionally understood under a term of CLI. --- Speaking from an experience writing CLIs for configuration-heavy embedded devices, the key design element of a functional CLI is a context-aware TAB expansion. This is what makes a CLI truly convenient for routine use. For example, if a mysql shell was smarter, it would've been allowing this: > use p<tab><enter> expands to "use production" > show c<tab> s<tab><tab><enter> expands to "show columns from secondary" > select * f<tab> s<tab><tab> ... expands to "select * from secondary ..." It would also be nice to make OS shell more aware of individual commands' options, and to allow for example: # ip addr <tab> shows "ip addr add" # <tab> shows "ip addr del" # <tab> shows "ip addr" This is possible through hardcoding these expansions into the shell, but that's not very elegant, is it? On the other hand allowing to integrate arbitrary commands with the shell in a generic way would require putting together some sort of interface/manifest contraption and it would most likely go against the very spirit of Unix simplicity. So catch 22 it is.
  • asolove 15y ago
    zsh has an extensible command/expansion system much like what you are asking for, allowing users to implement plugins documenting how to autocomplete commands, options, and data types passed to options (files, yes/no, etc.). It is fantastical.
  • lysol 15y ago
    If you switch to Postgres, psql (the commandline client) supports the features you're asking for. :)
  • mcantor 15y ago
    I think the use of "interface" is sensible, if somewhat ambiguous on the surface. In this context, options & arguments are the interface to the utility, not the "CLI", which is the interface to the command line itself. Context-aware tab completion is very doable in the unix world, actually; it's just a hassle on the part of the utility-writer. Have you ever noticed that if you add a new file "foo/bar/baz.py" to a mercurial repository and type "hg add fo<TAB>", it will autocomplete all the way to "foo/bar/baz.py", without stopping at each directory? This is because hg has overridden the default tab completion provided by bash and defined its own set of possibilities. I wish it were easier to set up; I think if that were the case, we'd see a lot more utilities with spot-on tab completion.
• mcantor 15y ago
  Oh, and another: Use your language's command-line option processing libraries. OptionParser in ruby and argparse in python. There is no reason to eschew these libraries: they're part of the standard library, they require zero coupling to your app logic, and they handle all of the edge cases for free. "But I can just shift the arguments", you say! Yeah? Great! What if the user pipes input through STDOUT? What if the user passes a flag, a required argument, and then another flag? Will your script read the last flag correctly, or has the naive logic already entered "required argument processing mode"? Just use the library. It's a solved problem!
  • antoarts 15y ago
    I choose not to discuss implementation in that article, but you should never reinvent the wheel (poorly).
    • mcantor 15y ago
      I think a lot of people don't even realize such libraries are out there, or don't understand that there's a wheel being reinvented. ("It's just command line options. Why would you need a whole library to do that?")
      • _delirium 15y ago
        Some of the wheels are also very big and crufty--- I would only link GNU Getopt to a C program if it were a Real Program, either with complex option processing or need for industrial-strength polish. For simple one-offs it's a lot easier to have 3 lines of strcmp(), and Getopt feels like overkill.
  • scott_s 15y ago
    And if you use C++ and are willing to use Boost, program_options: http://www.boost.org/doc/libs/1_47_0/doc/html/program_options.html http://www.boost.org/doc/libs/1_47_0/doc/html/program_option... I recognize that many people are not willing to use C++, and among those that are, many are still unwilling to use Boost, but I find the program_options library to be great. An example use that I think is reasonable and a big win over doing it myself: https://github.com/scotts/cellgen/blob/master/src/main.cpp#L305 https://github.com/scotts/cellgen/blob/master/src/main.cpp#L...
• mcantor 15y ago
  One more: Keep your "usage" blurb succinct and clear. Don't clobber your users' terminals with two pages of output when they're not expecting it. If "yourapp", "yourapp -h" or "yourapp --invalid-flag" results in two screenfuls of information containing your app's license, installation instructions, contribution notes, an exhaustive listing of every single one of the 100 available subcommands, and a verbose representation of a configuration setting that 75% of your users won't care about, you're doing it wrong. (I'm looking at you, rvm). This is similar to the idea of "You don't really understand something unless you can explain it so your grandmother gets it." Your app doesn't really have a sensible interface unless the top layer of its abstraction, or the most common commands, can be summarized in less than scrillions of lines of text. If you simply can't trim it down far enough, it's because you're breaking from the Unix philosophy and your utility is doing too much.
  • zwp 15y ago
    Also tedious: $ ls -Q ls: illegal option -- Q usage: ls -aAbBcCdeEfFghHiklLmnopqrRsStuUwxvV1@/[c | v]%[atime | crtime | ctime | mtime | all] [files] It's succinct but that second line is almost completely useless.
    • mcantor 15y ago
      One of my favorites is tar: $ tar -m foo tar: You must specify one of the `-Acdtrux' options Try `tar --help' or `tar --usage' for more information. Oh, right! `-Acdtrux'! How could I have forgotten. I deal with ACD Trucks all the time. (?!?!)
  • janus 15y ago
    Also I'm looking at you, rails.
  • ilikepi 15y ago
    Speaking of "usage" blurbs, for $DIETY's sake, please assume 80-character wide terminals.
• Pewpewarrows 15y ago
  One thing that always infuriates me: If I go to --help or the man page for your command, and don't see a real example of how to use it immediately, you've failed me as a user. Seeing your syntax tree and a list of every option and its description doesn't help me when I'm first trying to use your program. I just want to see one or two quick examples of real commands with a short sentence explaining each. After that I'll dive into the mess that is the dozens of flags and inputs to decipher exactly what I want.
  • pmr_ 15y ago
    It always struck me as odd that man pages tend to have the EXAMPLES section as the last section of the document. I really would like it the other way around but this kinda fits with a bottom-up approach to learning. Look at the small details then get the full picture and how it's supposed to be used.
  • code_duck 15y ago
    I've seen a few discussions of this around. I agree with you, but there are some who believe that examples do not belong in manages (not sure what their rationale is).
    • Nick_C 15y ago
      In my experience, it's from some GNU folk who like their god-forsaken abomination that is info docs.
  • Nick_C 15y ago
    man docs have a specific format, a followed by b followed by c, etc. Examples are towards the end, near bugs and author. It may not be how you want it, but at least it's consistent. shift-G will take you straight to the end, with hopefully some examples.
• alexis-d 15y ago
  I agree with most of the article, except the yes/no part. In fact I think it's better to do : "Do you want to do this (Y/n)?" Where the most common option is uppercase so I can just hit enter.
  • dmpatierno 15y ago
    The important point here is to at least require that <Enter> key, rather than just using getchar() or whatever else and continuing on unexpectedly.
• there 15y ago
  Do you really want to do this (y/n)? i would rather see this as Do you really want to do this (y/N)? capitalize the option that will be used by default if you hit enter with no other input.
  • fnl 15y ago
    I absolutely agree - and not only does the article barley scratch what is Unix standard anyways, and the more tricky questions such as piping, exit and error states, or the environment are left out. Kind of disappointing, in my opinion.
  • killerswan 15y ago
    I'm also used to seeing Do you want to do this? [n]:
• prostoalex 15y ago
  ESR's "The Art of Unix Programming" has a good section on consistent default of command line options http://www.catb.org/esr/writings/taoup/html/ch10s05.html http://www.catb.org/esr/writings/taoup/html/ch10s05.html
• gnufied 15y ago
  > Silence trumps noise How about, ec2-server-start -n 4 -t medium -i img-xxxg Which expands to start 4 medium instances using image img-xxxg. Will you prefer a long wait and then silently back on prompt or an indication of something happening? I agree with what he is saying, but I think there is a hint of unfair generalization here. > Naming your utility Again small unix commands are like precious three letter domain names. Not always viable. Also, although most of single letter commands are free, one should avoid to name a CLI binary in single letter, because 1. users often type single letter stuff by mistake. 2. users use single letter aliases.
  • shadearg 15y ago
    > Will you prefer a long wait and then silently back on prompt or an indication of something happening? This is what the -v, --verbose option is for. Without this flag, you should assume everything is operating as expected until you receive an error message or an exit status >0.
• salem 15y ago
  One cool feature of the juniper junos CLI is that all the CLI commands have an option for XML output, making parsing of the CLI output in scripts a little more sane.
  • rch 15y ago
    I've started adding an option to output a complete Galaxy tool config file for some CLI apps. -- http://wiki.g2.bx.psu.edu/Admin/Tools/Tool%20Config%20Syntax http://wiki.g2.bx.psu.edu/Admin/Tools/Tool%20Config%20Syntax
  • shabble 15y ago
    There was a project mentioned on HN fairly recently (~weeks ago) about an extended pipe system, using JSON and a bunch of common schemas, as I recall. Both http://acko.net/blog/on-termkit http://acko.net/blog/on-termkit and http://blogs.perl.org/users/rocco_caputo/2011/05/apppipefilters---json-in-the-shell.html http://blogs.perl.org/users/rocco_caputo/2011/05/apppipefilt... seem to fit what I was thinking of, but I'm sure there was something else. Nice ideas, but the inertia of existing unix tools is going to be hard to overcome, and a system isn't much use until all your common tools support it (or at least don't break it).
  • killerswan 15y ago
    I talked some folks into using JSON output for a tool, and am now in the midst of fixing both ends so that the output is valid JSON, instead of a newline delimited file with JSON on each line.......
• icebraining 15y ago
  "GUIs also have the advantage when it comes to presenting and editing information that is by nature graphical. This includes photo manipulation and watching movies (I have always wanted a program that shows a movie in my terminal by converting it to ASCII art in real-time, that would be sweet)." This is an interesting discussion - what is the CLI, exactly? My personal PDF viewer is Zathura[1], which is controlled like VIM. On the other hand, programs like Kismet run on a terminal, but have mouse controlled menus. Personally, I feel that Zathura is a CLI application, even though it depends on X, because the interaction is done in a keyboard driven way with no graphical widgets. [1]: http://pwmt.org/projects/zathura/ http://pwmt.org/projects/zathura/
  • a3_nm 15y ago
    True. I often use text-based applications because I can usually expect them to have a sensible and efficient interface which does not require the mouse. There are graphical applications which follow the same spirit, but they are pretty well hidden.
  • nitrogen 15y ago
    I have always wanted a program that shows a movie in my terminal by converting it to ASCII art in real-time, that would be sweet For the benefit of the original author, mplayer and xine both have ASCII art output modes (mplayer -quiet -vo aa, aaxine).
• Xurinos 15y ago
  The name should be short. A long name will be tedious to type, so don’t call you version control program my-awesome-version-control-program. Call it something short, such as avc (Awesome Version Control). $ my-aw<TAB> # yay! Personally, I am not a big fan of everyone using two or three-letter linux names for everything. We have a lot of options now for autocompletion and seeing what is available, so long names are no longer a talking point.
  • scott_s 15y ago
    $ may-aw<TAB> my-awe-inspiring-tool my-awwwww-how-cute-program my-awesome-version-control-prog my-aww-yeah-tool my-awchoo-i-sneezed-program my-aw-long-your-names-are-grandma Also, please don't make me hit the - character when I call your program.
    • Xurinos 15y ago
      I prefer - over _ over smashingwordstogether. There are the benefits of readability and not needing to intermittently press the shift key. Also, you might prefer bind 'tab:menu-complete' or to assign that to a different key. This allows you to quickly cycle through valid options so you are not playing "what's the next letter?" games.
• munificent 15y ago
  Examples include cd, calling it with no arguments returns you to the home directory. How did I never know that before?
  • a3_nm 15y ago
    Make sure you also know about cd - (go to previous directory) and cd foo bar in zsh (go to ${PWD/foo/bar}).
• mahmud 15y ago
  This might not be shared by others, but here it goes. If your CLI program is a file-format conversion utility, please include a way to dump meta-data, header formats, etc. Don't just silently convert from A to B, allow me to get at the info you have gathered from the input. For example, a binary disassembler SHOULD dump the executable header format. An spreadsheet converter utility SHOULD display how many sheets there are, if there are macros, how many rows, etc. One of my pet peeves is pdftotext, a very nifty utility that I use to convert PDF reports to ASCII for subsequent awking. pdftotext has an option to specify start and end pages to extract, but it doesn't have an -i or --info option that tells me how many pages a PDF file has. So, my scripts have a very high upper-limit, like 1000, and it converts the file page by page, until the output text page has a size of zero. Which reminds me, I should probably fork the fucker this weekend, now that I have some free time.
  • jsrn 15y ago
    "[...] but it doesn't have an -i or --info option that tells me how many pages a PDF file has" You could use pdfinfo - in Debian / Ubuntu, it is in the same package as pdftotext (poppler-utils). To extract (only) the number of pages of a PDF: $ pdfinfo FILE.pdf | grep '^Pages' | tr -s ' ' | cut -d ' ' -f 2
    • mahmud 15y ago
      Thank you. Now I don't have to hate people who leave blank pages without the customary "This page intentionally left blank".
• jcr 15y ago
  You might want to fix this typo. > Maybe it¿s just me, but I prefer to remotely control computers via SSH over VNC If you're really running "SSH over VNC" then you're doing it wrong. ;) > I have always wanted a program that shows a movie in my terminal by converting it to ASCII art in real-time, that would be sweet man mplayer and look for the -vo flag which controls the video output mode/driver. Two common options for video output (-vo) are the 'aa' (ASCII Art) and 'caca' (Color Coded ASCII Art). There is a third, 'bl' ("blinkenlights") but it's hardware dependent.
• rmccue 15y ago
  > Multi-letter options start with two hyphens, and each such argument must be separated with spaces. That's something that's always annoyed me about screen; commands such as "wipe" are "screen -wipe"
  • lell 15y ago
    there's "find ./ -type d", also (find directories only.)
    • ilikepi 15y ago
      'find' is an interesting animal: it* really only has a handful of traditional option parameters, and these are of the single-dash-single-letter variety. The single-dash-word parameters are all part of its expression language for selecting filesystem objects. * checked against /usr/bin/find on OS X 10.6.8 (which seems to lack an option parameter for printing its own version number) and GNU find 4.2.27
      • silentbicycle 15y ago
        'find' is one of the oldest Unix programs still in common use. Its standardized arguments predate modern conventions for command line arguments.
• rhizome 15y ago
  After -h --help, I think the most essential option is -n --dry-run
• ojilles 15y ago
  The article is interesting up to a point, but what really struck me is that this blog claims to be written by a 15 year old. I think the topics and depth of the other articles on the blog spell great things for this guy's future!
• uriel 15y ago
  See the paper by Rob Pike and Brian Kernighan 'Program Design in the UNIX Environment' (aka 'cat -v considered harmful'): http://harmful.cat-v.org/cat-v/ http://harmful.cat-v.org/cat-v/