7 ms·

Help Message for Shell Scripts

• diablerouge 6y ago
  This seems like a neat sed trick, but I'm not sure that it's useful for this particular case? When I write a shell script, I often write a help function if it's not a totally trivial script, but there's no need for this cryptic sed expression, right? You can just call `echo` a few times and do it the obvious way. That works better for maintainability and if you put it at the top of the file then it's immediately visible when opening or using `head` on it. Neat trick though - sed is super useful for all kinds of things. I had a co-worker who bound a keybinding to a sed one-liner that would automagically reconfigure some files that needed to be changed regularly. I ended up using that trick to allow for changing my terminal console colorscheme with a single command.
  • e12e 6y ago
    It's a little sad that standard shell here documents only support elliding leading tabs (it wouldn't be so sad if the record separator hadn't been thrown under the bus - having a character for indentation distinct from space is good... In theory). But at any rate my typical usage() is generally along these lines (warning watch out for expansions): usage() { cat - <<-EOF `basename ${0}`: demonstrate here docs Usage: `basename ${0}` <required argument> [-o|--optional-param] Etc. Possibly referencing default value: ${DEFAULT_VALUE} EOF }
    • jolmg 6y ago
      I think it'd be better without using basename, just $0. That way it matches the way it was called, which is how the user chose to access it for whatever reason. The bare filename might refer to a different command, even. Also, if you include examples in the help text, they'll also be able to copy and paste, instead of having to manually insert what basename stripped away.
      • e12e 6y ago
        True enough - I find it depends a bit on the nature of the script - if it's something buried under misc/tools/extra/bin/util.sh - i tend to prefer brevity - especially in the first paragraph/usage section (util.sh <required param> [optional param]). But for more concrete examples I'll often leave off the basename - for easier cut and paste.
  • zzzcpan 6y ago
    Right, it's a bit useless trick. I guess the author is just exploring how to organize help, maybe thinking about larger scripts or maybe doing it for the article. Either way it's hard to see it going anywhere with sed. If you were to explore parsing and organizing help, I'd suggest starting with a simple pure shell loop like this: while read -r line; do case "$line" in "###"*) echo "${line#\###}" ;; esac done <"$0"
• jandrese 6y ago
  Hmm: % sed -rn 's/^### ?//;T;p' testfile sed: 1: "s/^### ?//;T;p": invalid command code T Looks like it might need GNU Sed or something. But honestly if I want to read the top of the file less works just as well.
  • adrianmonk 6y ago
    Yeah, "man sed" on my machine says, "This is a GNU extension." You could do the same thing with awk instead: awk '{ if (sub("^### ?", "")) { print; } else { exit; } }'
    • bewuethr 6y ago
      Or sed -rn 's/^### ?//p'
      • e12e 6y ago
        Doesn't appear anyone has tried addressing before replacement - ie the simplest sed work-a-like - if you don't mind the leading ### is just: sed -n '/^### /p' I believe? (equivalent to grep). Then eg: sed -nr '/^### /s/^.{4}(.*)/\1/p' (or without the redundant addressing, just:) sed -nr 's/^### (.*)/\1/p'
        • bewuethr 6y ago
          You can simplify sed -nr 's/^.{4}(.*)/\1/' to sed -nr 's/^.{4}// And if you use a pattern for the address, you can repeat it in the substitution by using an empty pattern, so sed -nr '/^### /s/^.{4}(.*)/\1/p' is the same as sed -nr '/^### /s/^.{4}//p' is the same as sed -nr '/^### /s///p' at which point I prefer just the substitution: sed -nr 's/^### //p'
    • jandrese 6y ago
      Well sure, there are tons of ways to do this in other languages. :) Perl for example was made for problems like this. perl -ne 'print if ( s/^### ?// )'
• adrianmonk 6y ago
  You can also use a "here document" help() { cat <<'EOH' my-script — does one thing well Usage: my-script <input> <output> Options: <input> Input file to read. <output> Output file to write. Use '-' for stdout. -h Show this message. EOH } If the indentation bugs you, you can use a simpler sed trick to remove leading space so that you can indent it as desired: help() { sed -e 's/ //' <<'EOH' my-script — does one thing well Usage: my-script <input> <output> Options: <input> Input file to read. <output> Output file to write. Use '-' for stdout. -h Show this message. EOH }
  • psophis 6y ago
    You can also use add a hyphen ( <<-EOF ) to suppress leading tabs but not spaces. https://linuxhint.com/bash-heredoc-tutorial/ https://linuxhint.com/bash-heredoc-tutorial/
    • yjftsjthsd-h 6y ago
      Oh, that's nice! And in spite of the labeling on that page, it doesn't seem to be a BASHism; it at least works in dash, too.
      • e12e 6y ago
        And ksh.
    • smichel17 6y ago
      I've always avoided that for fear that my or someone else's editor will accidentally replace the tabs with space. Mixed is not a common configuration, these days.
      • account42 6y ago
        This makes me want to use this just to get people to fix their broken editors.
• mey 6y ago
  Handling of arguments is one of the reasons I reach for Python or Powershell instead of a bash script when writing my own stuff. https://docs.python.org/3/library/argparse.html https://docs.python.org/3/library/argparse.html is great. Powershell has the Param keyword that functions like argparse in Python https://docs.microsoft.com/en-us/powershell/module/microsoft.powershell.core/about/about_functions_advanced_parameters?view=powershell-7 https://docs.microsoft.com/en-us/powershell/module/microsoft...
  • acdha 6y ago
    My rule for a long time has been that any time you have more than one screen's worth of code and/or are using any of arrays, functions, or more than simple positional arguments you'll save time by rewriting it in Python. shellcheck has helped soften that a bit but the usability difference is pretty noticeable even with multiple decades writing shell scripts.
  • dragonwriter 6y ago
    > https://docs.python.org/3/library/argparse.html https://docs.python.org/3/library/argparse.html is great Argparse is okay (and being in stdlib makes it always-available), but it's no click. https://click.palletsprojects.com/en/7.x/ https://click.palletsprojects.com/en/7.x/
    • 40four 6y ago
      Thumbs up for 'Click'. I used it for a project once, and I was really happy with it. Easy to use, good docs. Would use it again.
      • pletnes 6y ago
        It’s fantastic and should be used by most CLI programs. Argparse is much faster and avoids having a dependency, so it does serve a purpose.
      • gavinray 6y ago
        Googling the library appears to be about ~8,000 lines of code (core.py is ~2,000 alone). Is that really reasonable sounding to most people for parsing CLI input/output and display manpages or helptext?
• xvolter 6y ago
  I also posted to the github gist, this the sed command here is not cross-plataform friendly. You can accomplish the same thing with an awk command though: awk '/^###/' "$0"
  • jpxw 6y ago
    Nice, this is much cleaner
  • pwdisswordfish2 6y ago
    sed -n '/^###/p' is cross-platform friendly.
    • u801e 6y ago
      This will also work: sed '/^###/!d'
      • pwdisswordfish2 6y ago
        This will also work: sed '/^#\{3\}/!d'
  • yesenadam 6y ago
    This also strips the leading hashes + optional space: awk 'sub("^### ?","")' "$0"
  • ddevault 6y ago
    The bit at the end isn't POSIX sh, either. Fixed version: if [ $# -eq 0 ] || [ "$1" = "-h" ]; then help exit 1 fi Relevant spec bits: https://pubs.opengroup.org/onlinepubs/9699919799/utilities/test.html https://pubs.opengroup.org/onlinepubs/9699919799/utilities/t...
• stkai 6y ago
  Handy! Now, can it author the help text as well? ;)
• ahnick 6y ago
  I like the idea of combining the header with the help documentation to reduce the number of areas to maintain in smaller scripts. For larger scripts though, I think I'd still prefer to have a separate function, so that the help documentation doesn't overwhelm the initial viewing of the actual code. I also like to feed a heredoc directly into man, which allows you to achieve nicer formatting for the help documentation. Something like this... man -l - << EOF .\" Manpage for encpass.sh. .\" Email contact@plyint.com to correct errors or typos. .TH man 8 "06 March 2020" "1.0" "encpass.sh man page" .SH NAME encpass.sh \- Use encrypted passwords in shell scripts ... EOF See encpass.sh for a working example of this -> https://github.com/plyint/encpass.sh/blob/master/encpass.sh https://github.com/plyint/encpass.sh/blob/master/encpass.sh
  • sicromoft 6y ago
    Note that this doesn't work on macOS, where the builtin `man` command doesn't support the `-l` option.
    • ahnick 6y ago
      Ah interesting, is there any workaround for Mac? Otherwise, I may just have to fallback to stripping the man page formatting and sending it to less.
      • enriquto 6y ago
        > is there any workaround for Mac? Yeah, any regular unix will do, for example openbsd, freebsd or any linux distribution.
      • tobylane 6y ago
        If I understand your need correctly: pandoc.
        • ahnick 6y ago
          pandoc is not installed on macOS out-of-the-box though right? The user would have to pull via homebrew or something?
• 7786655 6y ago
  Pretty sure this won't work if the script is called via $PATH
  • pwdisswordfish2 6y ago
    x=$(command -v $0 2>/dev/null) sed -rn 's/^### ?//;T;p' $x Personally I would not use the author's chosen sed commands. exec sed -n '/^###/p' $x would work fine.
• heinrichhartman 6y ago
  I like to do: help() { cat $0 } "May the source be with you." : )
• deleted 6y ago
  [deleted]
• sneak 6y ago
  Why is “./script.sh -h” better than “less script.sh”?
  • mttpgn 6y ago
    I just spent three days explaining a bash script I authored to a tech lead who "doesn't know bash that well". If I had written in more help messages I probably could have preserved more of my time.
  • soraminazuki 6y ago
    If you use zsh, you can use the help output to generate completions for your own scripts. https://github.com/zsh-users/zsh-completions/blob/master/zsh-completions-howto.org#completing-generic-gnu-commands https://github.com/zsh-users/zsh-completions/blob/master/zsh...
• oweiler 6y ago
  This is not elegant, this is an ugly hack at best.
• raggi 6y ago
  I used this strategy in "fx" which is a development helper frontend for fuchsia builds and tools. I used four # for the "short description" and three for the long description. The reason I used the strategy there is that lot of our scripts delegate arguments to native commands, and so adding help purely to --help wasn't really a good ROI. Implementation: https://fuchsia.googlesource.com/fuchsia/+/refs/heads/master/scripts/fx#40 https://fuchsia.googlesource.com/fuchsia/+/refs/heads/master...
• OliverJones 6y ago
  Cool. I did this on 7th Edition UNIX in 1977. I forget how. It's interesting that .... * NIX makes people do creative things All that Bell Labs stuff still works the way it always did. * People are still reinventing this particular wheel, and * This embedded help stuff still somehow hasn't made it into the infrastructure along with autocomplete.
• flaxton 6y ago
  Didn't work on macOS (multiple sed errors - switches differ from Linux) but prompted me to write a help function ;-)
  • gfosco 6y ago
    I have a project that makes heavy use of sed.. On macOS, I `brew install gnu-sed` and use `gsed` instead, so it works like other platforms.
    • flaxton 6y ago
      Nice! I will check that out.
  • ivan_ah 6y ago
    here is a gist that works on macOS (using `awk` instead of sed) https://gist.github.com/ivanistheone/0454191800c9caad77a52e0e29c8f31f https://gist.github.com/ivanistheone/0454191800c9caad77a52e0...
• jeffrom 6y ago
  Something I've wanted to do for a while is build a library to parse and generate use lines / documentation that adheres to the posix useline spec (can't find the link at the moment) while also being able to idempotently (de)serialize and be descriptive enough to define arguments and flags in a way a human could easily understand. iirc the spec seemed probably too vague to just work with all the currently existing man pages, but it would be nice to have a spec all programs can follow that machines can parse on my os.
  • layoutIfNeeded 6y ago
    http://docopt.org/ http://docopt.org/ ?
• j1elo 6y ago
  I learnt the same trick some years ago, from an article called Shell Scripts Matter: https://dev.to/thiht/shell-scripts-matter https://dev.to/thiht/shell-scripts-matter So I took some of the advice and tips offered in there, and wrote a template file to be used as a baseline when writing scripts for any project that might need one: https://github.com/j1elo/shell-snippets/blob/master/template.sh https://github.com/j1elo/shell-snippets/blob/master/template... Other resources that I link in the readme of that repo, because they were a great guide to write better and more robust scripts, are: - Writing Robust Bash Shell Scripts: https://www.davidpashley.com/articles/writing-robust-shell-scripts/ https://www.davidpashley.com/articles/writing-robust-shell-s... - Common shell script mistakes: http://www.pixelbeat.org/programming/shell_script_mistakes.html http://www.pixelbeat.org/programming/shell_script_mistakes.h... - Bash Pitfalls: http://mywiki.wooledge.org/BashPitfalls http://mywiki.wooledge.org/BashPitfalls - The Bash Hackers Wiki: https://wiki.bash-hackers.org/ https://wiki.bash-hackers.org/ EDIT: -for anyone who would like to read some actual examples- I have to manage a bunch of scripts so actually a slightly more up to date version of the template is put into practice by means of a common bash.conf file that then gets sourced by all scripts: https://github.com/Kurento/adm-scripts/blob/master/bash.conf.sh https://github.com/Kurento/adm-scripts/blob/master/bash.conf...
  • themodelplumber 6y ago
    Thank you for this really helpful comment. It's like an encyclopedia's worth of bash information in one go--much appreciated.
    • j1elo 6y ago
      You're welcome! Shell scripting has a weird language, unsafe by default, and very prone to mistakes... but knowing it well pays off. People say that for complex things it's better to write Python, but that doesn't fly in embedded or Docker environments. Python is not even present in the default Ubuntu Docker images. Also if all you want to do is really write glue code between CLI programs, shell scripting is the way to go. Happy coding!
      • 6y ago
• owenshen24 6y ago
  Unrelated: Is there any connection between the author and the other sam[]zdat who writes about society and other intriguing topics? https://samzdat.com/ https://samzdat.com/
  • krick 6y ago
    I wouldn't know, but there is no reason for me to be thinking something like that. "Samizdat" is not really a name or something, it's a transliteration of "самиздат", which is a short/colloquial for "самостоятельное издательство", which literally means "self-publishing" (this was a thing during the USSR, where "self-publishing" was basically opposed to "real, official government-approved publishing"). I believe it's just a "clever" domain somebody was able to acquire, nothing more.
    • owenshen24 6y ago
      Ah, thanks for the explanation.
• thangalin 6y ago
  There's an endless variation on how shell scripts can present help information. Here's another, consider this array: ARGUMENTS+=( "a,arch,Target operating system architecture (amd64)" "b,build,Suppress building application" "o,os,Target operating system (linux, windows, mac)" "u,update,Java update version number (${ARG_JRE_UPDATE})" "v,version,Full Java version (${ARG_JRE_VERSION})" ) The lines are machine-readable and alignment is computed by the template: https://github.com/DaveJarvis/scrivenvar/blob/master/build-template#L186 https://github.com/DaveJarvis/scrivenvar/blob/master/build-t... When install script[0] help is requested, the following is produced: $ ./installer -h Usage: installer [OPTIONS...] -V, --verbose Log messages while processing -h, --help Show this help message then exit -a, --arch Target operating system architecture (amd64) -b, --build Suppress building application -o, --os Target operating system (linux, windows, mac) -u, --update Java update version number (8) -v, --version Full Java version (14.0.1) Using an array reduces some duplication, though more can be eliminated. Scripts typically have two places where the arguments are referenced: help and switch statements. The switch statements resemble: https://github.com/DaveJarvis/scrivenvar/blob/master/installer#L191 https://github.com/DaveJarvis/scrivenvar/blob/master/install... Usually parsing arguments entails either assigning a variable or (not) performing an action later. Introducing another convention would allow hoisting the switch statement out of the installer script and into the template. Off the cuff, this could resemble: ARGUMENTS+=( "ARG_ARCH,a,arch,Target operating system architecture (amd64)" "do_build=noop,b,build,Suppress building application" "ARG_JRE_OS,o,os,Target operating system (linux, windows, mac)" "ARG_JRE_UPDATE,u,update,Java update version number (${ARG_JRE_UPDATE})" "ARG_JRE_VERSION,v,version,Full Java version (${ARG_JRE_VERSION})" ) The instructions to execute when arguments are parsed are thus associated with the arguments themselves, in a quasi-FP style. This approach, not including the FP convention, is discussed at length in my Typesetting Markdown series[1]. [0]: https://github.com/DaveJarvis/scrivenvar/blob/master/installer https://github.com/DaveJarvis/scrivenvar/blob/master/install... [1]: https://dave.autonoma.ca/blog/2019/05/22/typesetting-markdown-part-1/ https://dave.autonoma.ca/blog/2019/05/22/typesetting-markdow...
• hansdieter1337 6y ago
  Even better: Don’t use bash. I started using Python instead of bash. It’s way better to read and more maintainable. If I need the performance of native-Unix commands, I can still use them using subprocess.
  • drewbug 6y ago
    bash is everywhere
    • nhumrich 6y ago
      So is python
      • zeroimpl 6y ago
        But which python?
      • fredfjohnsen 6y ago
        No, it's not. https://tidbits.com/2019/06/25/apple-to-deprecate-scripting-languages-in-future-versions-of-macos/ https://tidbits.com/2019/06/25/apple-to-deprecate-scripting-...
  • ben509 6y ago
    Python is surprisingly bad at managing subprocesses, though. Read the subprocess docs closely, it's quite easy to get deadlocks if you try to compose operations the way you can in bash.
    • aflag 6y ago
      There are libraries that fix that: https://pypi.org/project/sh/ https://pypi.org/project/sh/ if you are in position to use external libraries.
  • ChAns0n 6y ago
    Python is not as handy/efficient as bash when you want to utilize some existing Unix commands. And normally it’s crucial to stop bleeding fast if something bad is happened to you server/cluster
• dougdonohoe 6y ago
  We do this for Makefile entries - looking for '##' that we put before each make command. ## help: prints this help message help: @echo "Usage: \n" @egrep -h "^## [a-zA-Z0-9\-]*:" ${MAKEFILE_LIST} | sed -e 's/##//' | column -t -s ':' | sed -e 's/^/ /' ## build: builds JAR with dependencies build: mvn compile
• fomine3 6y ago
  I'm particular about: If I run a command and its arguments is wrong, it should output error and help messages to STDERR. But if I run a command with --help argument, it should output help messages to STDOUT.
• deleted 6y ago
  [deleted]
• xelxebar 6y ago
  This reminds me of a nice sed one-liner I recently happened to craft. Do you ever collect families of functions in your shell scripts under different sections? Here's a nice way of printing out all the functions under a given section: funs(){ sed -n '/^## /h;x;/'"$1"'/{x;s/^\(\w\+\)().*/\1/p;x};x' "$0";} Where "sections" are delimited by comments of the form "## Section Name" at the beginning of a line. A particularly nice use case is when you write scripts that expect "subcommand" arguments, like $ foo.sh bar baz and wish to keep track of the available subcommands in the help documentation. Simply collect all your subcommands under the heading "## Subcommands" and stick a funs call in your documentation: usage=$(cat <<USAGE Usage: foo <subcommand> Subcommands: $(funs Subcommands) USAGE ) The sed one-liner above uses the oft-ignored "hold space" which lets you store data that persists between lines. Here's the same sed but expanded with comments: funs(){ sed -n '/^## /h # Store header line in hold space x # Swap out current line with header in hold space. /'"$1"'/{ # Run block if last encountered header matches $1 x # Return to processing current line (instead of header) s/^\(\w\+\)().*/\1/p # Print function names x # Whether or not this block runs, we want to return to # processing the current line. If the block does not # run, then the hold space contains our current line # with the active line being our header. So we must } # return to that state as whell when the block is run. x # Restore current line from hold space' "$0" }
• deleted 6y ago
  [deleted]
• gorgoiler 6y ago
  The power is out on your boat, again. It’s 3am. You suspect that, again, the alternator housing has come loose. You duct tape a flashlight to the bulkhead so you can work hands free and actually see what you are doing. All you have on you is a broken pocket knife but it’ll do because all you need to accomplish right now is to tighten the housing screws enough. You know this for a fact because you’ve done it three times already in the last 24 hours. It’s not even a documented procedure — you’ll replace the housing mounts entirely when you’re back at port in three days’ time. You guarantee it — this is the first thing you’ll do even, when you get back to shore. You have my word on that, captain! The duct tape came unstuck. It was damp and doesn’t work so well (at all) when it’s wet. The flashlight survived the fall. More tape this time should do the job. Tape mount version 2 will still unstick of course, eventually. Nothing stops the damp at sea, but if you use enough tape then you’ll have fixed the power by the time the tape fails. That’s your plan B and you’re sticking to it. Sure, you could do this job better if you had an impact driver with an automatically illuminated bit chuck, but buying one of those is further down the todo list than fixing the power on the boat, making it back to port, and ensuring the power doesn’t fail this way again, as promised. Or at least won’t fail for the next few shifts. On your days off you relax by programming in Bash.
  • chrisweekly 6y ago
    +1 for the sailing analogy! "Necessity is the mother of invention" must have been coined by a sailor.
• andsens 6y ago
  My time to shine! I built an argument parser that uses a POSIX compliant help message as the input. It's a parser generator really. It generates minified bash that is inlined in your script, so no dependencies. The work is based off of docopt (and is docopt compliant). Check it out: https://github.com/andsens/docopt.sh https://github.com/andsens/docopt.sh
• account42 6y ago
  > $0 means a filename of a file that is being executed. This is only a convention and is entirely up to the calling program. For example in bash scripts you can use `exec -a name ...` to pass "name" as the 0th argument. If you are already using #!/bin/bash you might as well use ${BASH_SOURCE[0]} to get the path to the current script.