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 1388 days ago [-]
+1 for the sailing analogy!
"Necessity is the mother of invention" must have been coined by a sailor.
adrianmonk 1389 days 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
}
pavon 1388 days ago [-]
Or just a multiline string:
#!/bin/bash
USAGE="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.
"
help() {
echo "$USAGE"
}
This is my standard approach which is cleaner for putting the documentation at the very top of the file like the linked article.
sillysaurusx 1388 days ago [-]
Thank you! I had no idea that multiline strings were valid bash.
rkangel 1388 days ago [-]
It's the same logic that allows you to type:
git commit -m "First line of commit
Second line of commit"
That's a multi-line string in bash.
GordonS 1388 days ago [-]
Woah, I had no idea multiline strings were even a thing in Bash, I've been using heredocs for help messages since forever!
Do you know if these are portable?
pavon 1388 days ago [-]
As far as I know. The POSIX spec[1] simply declares that in single quotes all characters will be preserved exactly, except for single quotes, which aren't allowed. Likewise, for double quotes, except that it also performs expansions ($) and allows escaping (\).
That's exactly what I do. For others who were not aware that multi-line strings can be used, this is POSIX-compatible (most of my shell scripts are executed by `dash`).
tuatoru 1388 days ago [-]
This is one (useful!) interpretation of "code should be self-documenting". Just put the documentation into strings.
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 1388 days ago [-]
This makes me want to use this just to get people to fix their broken editors.
yjftsjthsd-h 1389 days 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.
a commonly used feature that has been a part of the unix standard since before "bash" only meant to hit something with a heavy object, while linus was getting his diaper changed is not an "obscure feature."
a five year old took his first aware car ride, and at a gas station saw the trunk of the car next to theirs open. he said "seriously, bmw has too many obscure features." after all, a car for him was where you put the baby seat. and why would you put that in a compartment with no windows or air, that's too small to even fit a baby seat.
did you enjoy the ride?
koala_man 1388 days ago [-]
I believe the point of the article's method is that it allows you to document your script with code comments, and then reuse the same text for help output
jolmg 1388 days ago [-]
The neat thing about not indenting it is that you can make use of your editor's text-width auto-wrapping. For example, if you have it set to 80 columns, indenting it would make the text-width of the help text 76 in your case.
Also, putting the help text in code like this instead of a comment allows one to expand $0 so that the command name in the help text always matches the filename and path used in the invocation.
1388 days ago [-]
amelius 1388 days ago [-]
But now the sed line bugs me ;)
ElCampechano 1388 days ago [-]
Or just write it in Python.
hedora 1388 days ago [-]
Python is terrible at one liners. The sed is much more compact.
emmelaich 1388 days ago [-]
Multiline strings means you don't need sed or anything.
j1elo 1388 days ago [-]
I learnt the same trick some years ago, from an article called 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:
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...
themodelplumber 1388 days ago [-]
Thank you for this really helpful comment. It's like an encyclopedia's worth of bash information in one go--much appreciated.
j1elo 1388 days 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!
mercer 1388 days ago [-]
I'll second the thanks. Thanks!
maddyboo 1388 days ago [-]
A bash pitfall which I have experienced but didn’t see mentioned is the behavior of the `set -e` (errexit) option when using command substitution. If you expect failures within the command substitution to cause the script to exit, you’re gonna be confused.
Thanks. I wasn't aware of that option. I've added the following to my Bash-specific shell scripts:
# Cause command substitution to inherit the value of the `errexit` option.
# Introduced in Bash 4.4
if [ "${BASH_VERSINFO[0]}" -gt 4 ] ||
{ [ "${BASH_VERSINFO[0]}" -eq 4 ] && [ "${BASH_VERSINFO[1]}" -ge 4 ]; }; then
shopt -s inherit_errexit
fi
mey 1389 days 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.
while (( $# )); do
case "$1" in
-h|--help)
usage
exit
;;
-v|--version)
do_version
exit
;;
-d|--debug)
debug=true
;;
-a|--arg)
arg_value="$2"
shift
;;
*)
if [[ ! -v pos1 ]]; then
pos1="$1"
elif [[ ! -v pos2 ]]; then
pos2="$1"
else
>&2 printf "%s: unrecognized argument\n" "$1"
>&2 usage
exit 1
fi
esac
shift
done
bewuethr 1388 days ago [-]
The one downside of this is that it doesn't handle squeezing flags as in
foo -da bar
whereas getopts does. On the other hand, with (the Bash built-in) getopts you're limited to single character flags.
Spivak 1388 days ago [-]
You can do that it will just make things a little less pretty.
while (( $# )); do
case "$1" in
-*h*|--help)
do_help
exit
;;
-*v*|--version)
do_version
exit
;;
-*d*|--debug)
debug=true
;;&
-*a*|--arg)
value="$2"
shift
;;&
esac
shift
done
It doesn't support args of the form -avalue but those a pretty uncommon anyway.
jolmg 1387 days ago [-]
That wouldn't work in the general case. Those patterns would also match long options. If I add a case pattern `--all)`, and I call the script with `--all`, it's also going to match
-*a*|--arg)
You could fix that with:
-a*|-[!-]*a*|--arg)
> It doesn't support args of the form -avalue but those a pretty uncommon anyway.
You could
-a*|-[!-]*a*|--arg)
if [[ "$1" != --arg ]]; then
value="${1#*a}"
fi
if [[ ! "$value" ]]; then
value="$2"
shift
fi
;;&
Putting the option stuck together to its value has the advantage of working nicely with brace expansion. For example, you can call `strace -p{1111,2222,3333}` to trace those 3 pids and avoid having to type `-p` 3 times.
jolmg 1387 days ago [-]
As a final addendum, case clauses of options that take arguments like -a/--arg should not be terminated with `;;&`, but rather with `;;`.
Spivak 1386 days ago [-]
This is awesome! Thank you for being a total bash nerd.
jolmg 1385 days ago [-]
There's still one problem. To exemplify it, if you call with `-av`, it'll process the `v` as the option `-v` instead of the option value to `-a`. If you only have one possible option that takes a value, this can be fixed by putting its case clause before all others. If you have more, then that'll require things to get a little more complicated:
-d*|-[!-]*d*|--debug)
if [[ ! "$finished_case" && ("$1" = --debug || "$1" =~ '^[^ad]*d') ]]; then
debug=true
fi
;;&
-a*|-[!-]*a*|--arg)
if [[ ! "$finished_case" && ("$1" = --arg || "$1" =~ '^[^a]*a') ]]; then
if [[ "$1" != --arg ]]; then
value="${1#*a}"
fi
if [[ ! "$value" ]]; then
value="$2"
shift
fi
finished_case=true
fi
;;&
...
esac
shift
finished_case=
done
All case-clauses would need to use `;;&` by the way, including `-v` and `-h`. The regex is generally:
Another problem is that option and argument non-recognition would not work as previously layed out. You can include short options that aren't recognized, and they'll be ignored instead of raising errors. For positional arguments, one would need a condition to check for options, since using `;;&` for everything means that everything would land to
*)
Maybe those are the last issues, but this is already out of hand for otherwise small and simple shell scripts. All these complications arise from trying to support the sticking together of short options and their possible values. Processing arguments in a case loop is much, much simpler if we avoid supporting those 2 features.
This is why I love the HN community, learning something new every day. (Happy 10,000) I use argparse because it is stdlib, but will checkout click!
40four 1389 days 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.
gavinray 1388 days 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?
dastx 1388 days ago [-]
I suppose it depends on the use case. Personally I've always thought argparse is good enough, and have never hit a roadblock "because I'm using argparse" so to say. Having said that, I do like the pattern click is going for. If it argparse allowed the same pattern, in my opinion that would be cool, and it would probably be my first choice.
blondin 1388 days ago [-]
argparse should not be the first thing to reach for, imo, when good old sys.argv can do the job.
mey 1388 days ago [-]
At that point I wouldn't leave bash. I feel like argparse allows for better documentation, error handling and input validation.
40four 1386 days ago [-]
I didn’t mean to suggest we should reach for Click for simple help/manpage display.
The case I used it for was much more complex. What I liked about it was the easy to use API, clear documentation & examples, and readable patterns.
For simple text display, I like the solution from the article, and I learned something new about bash scripts. Also, I learned from comments you can use heredoc in bash!
meddlepal 1388 days ago [-]
I'm not trying to be antagonistic here... but who cares how many lines it has unless you plan to maintain it?
pletnes 1388 days 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.
A great option when you're stuck with an old crusty script that you don't want to completely rewrite in python, but do want to clean up enough so that you can call it with `-h` and remember how to use it a few months in the future.
Unfortunately, this won't help you if you're on embedded where python isn't in the base system.
sidpatil 1387 days ago [-]
PowerShell also has comment-based help, which is like a manpage embedded as a comment within the script. It's like OP's suggested help format, but better.
I also really like the "flag" package for Go, it generates the help text for you and easily lets you set defaults as well as helps you type-check inputs.
Cool, I'll check it out. There's something attractive about using stuff from the standard library though.
acdha 1389 days 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.
daitangio 1388 days ago [-]
Try pyhon click: from flask& jinja2 author, it is very nice
diablerouge 1389 days 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 1389 days 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):
I think it'd be better without using basename, just $0. That way it matches the way it was called, which is how the user chose to access it for whatever reason. The bare filename might refer to a different command, even. Also, if you include examples in the help text, they'll also be able to copy and paste, instead of having to manually insert what basename stripped away.
e12e 1388 days ago [-]
True enough - I find it depends a bit on the nature of the script - if it's something buried under misc/tools/extra/bin/util.sh - i tend to prefer brevity - especially in the first paragraph/usage section (util.sh <required param> [optional param]).
But for more concrete examples I'll often leave off the basename - for easier cut and paste.
zzzcpan 1388 days ago [-]
Right, it's a bit useless trick. I guess the author is just exploring how to organize help, maybe thinking about larger scripts or maybe doing it for the article. Either way it's hard to see it going anywhere with sed. If you were to explore parsing and organizing help, I'd suggest starting with a simple pure shell loop like this:
while read -r line; do
case "$line" in
"###"*)
echo "${line#\###}" ;;
esac
done <"$0"
dougdonohoe 1388 days 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
xvolter 1389 days 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"
ddevault 1388 days ago [-]
The bit at the end isn't POSIX sh, either. Fixed version:
if [ $# -eq 0 ] || [ "$1" = "-h" ]; then
help
exit 1
fi
This also strips the leading hashes + optional space:
awk 'sub("^### ?","")' "$0"
pwdisswordfish2 1388 days ago [-]
sed -n '/^###/p' is cross-platform friendly.
u801e 1388 days ago [-]
This will also work:
sed '/^###/!d'
pwdisswordfish2 1387 days ago [-]
This will also work:
sed '/^#\{3\}/!d'
jpxw 1388 days ago [-]
Nice, this is much cleaner
account42 1388 days 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.
xelxebar 1388 days 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:
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"
}
fomine3 1388 days 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.
ahnick 1388 days 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
So you could do it "manually" that way. Not the cleanest or prettiest solution but it's much lighter weight than using something like pandoc.
EDIT: Full example:
{ /usr/bin/tbl | /usr/bin/groff -Wall -mtty-char -Tascii -mandoc -c | /usr/bin/less -is; } <<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
ahnick 1388 days ago [-]
Thanks, this worked well on Mac.
tobylane 1388 days ago [-]
If I understand your need correctly: pandoc.
ahnick 1388 days ago [-]
pandoc is not installed on macOS out-of-the-box though right? The user would have to pull via homebrew or something?
enriquto 1388 days ago [-]
> is there any workaround for Mac?
Yeah, any regular unix will do, for example openbsd, freebsd or any linux distribution.
lolsal 1388 days ago [-]
> so that the help documentation doesn't overwhelm the initial viewing of the actual code.
That is a very strange argument to me. You find that more cumbersome than jumping around to random functions?
ahnick 1388 days ago [-]
No, I think the readability of the help documentation itself is largely the same whether it is placed in the header or in a dedicated function. When I'm viewing the shell script code though, often I want to jump right in and see the actual code, not look at the help documentation.
By having the help documentation in a function in the middle or towards the end of the file, I don't have to page down through the help documentation to get to the code that is actually doing things. If I'm really interested in the help documentation, then I'd prefer to look at the nicely formatted version output by the script (<script> --help or whatever) rather than looking in the actual script code anyway.
Admittedly, this may be more of a subjective personal preference item.
hansdieter1337 1388 days 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.
ChAns0n 1388 days 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
argonauts12 1387 days ago [-]
I've been migrating shell scripts to python and have found the 'sh' library invaluable for pulling in pure CLI commands from the bash script and adding to the python implementation. http://amoffat.github.io/sh/
It's essentially an abstraction layer above subprocess. Quick example - to use ifconfig natively in python:
from sh import ifconfig print(ifconfig("wlan0"))
ben509 1388 days 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 1388 days ago [-]
There are libraries that fix that: https://pypi.org/project/sh/ if you are in position to use external libraries.
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...
jandrese 1389 days 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 1389 days ago [-]
Yeah, "man sed" on my machine says, "This is a GNU extension."
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/^### ?// )'
bewuethr 1389 days ago [-]
Or
sed -rn 's/^### ?//p'
e12e 1388 days 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 1388 days 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'
1388 days ago [-]
heinrichhartman 1388 days ago [-]
I like to do:
help() { cat $0 }
"May the source be with you." : )
1388 days ago [-]
OliverJones 1388 days 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.
jeffrom 1388 days 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.
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
flaxton 1388 days ago [-]
Didn't work on macOS (multiple sed errors - switches differ from Linux) but prompted me to write a help function ;-)
gfosco 1388 days 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 1388 days ago [-]
Nice! I will check that out.
ivan_ah 1388 days ago [-]
here is a gist that works on macOS (using `awk` instead of sed)
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 1383 days ago [-]
Ah, thanks for the explanation.
7786655 1388 days ago [-]
Pretty sure this won't work if the script is called via $PATH
pwdisswordfish2 1388 days ago [-]
x=$(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' $x
would work fine.
1388 days ago [-]
sneak 1388 days ago [-]
Why is “./script.sh -h” better than “less script.sh”?
soraminazuki 1388 days ago [-]
If you use zsh, you can use the help output to generate completions for your own scripts.
I just spent three days explaining a bash script I authored to a tech lead who "doesn't know bash that well". If I had written in more help messages I probably could have preserved more of my time.
stkai 1388 days ago [-]
Handy! Now, can it author the help text as well? ;)
thangalin 1388 days ago [-]
There's an endless variation on how shell scripts can present help information. Here's another, consider this array:
ARGUMENTS+=(
"a,arch,Target operating system architecture (amd64)"
"b,build,Suppress building application"
"o,os,Target operating system (linux, windows, mac)"
"u,update,Java update version number (${ARG_JRE_UPDATE})"
"v,version,Full Java version (${ARG_JRE_VERSION})"
)
The lines are machine-readable and alignment is computed by the template:
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:
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].
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.
"Necessity is the mother of invention" must have been coined by a sailor.
git commit -m "First line of commit
Second line of commit"
That's a multi-line string in bash.
Do you know if these are portable?
[1]https://pubs.opengroup.org/onlinepubs/9699919799/utilities/V...
And Ruby 2.5 has an enhancement which preserves leading whitespace.
a five year old took his first aware car ride, and at a gas station saw the trunk of the car next to theirs open. he said "seriously, bmw has too many obscure features." after all, a car for him was where you put the baby seat. and why would you put that in a compartment with no windows or air, that's too small to even fit a baby seat.
did you enjoy the ride?
Also, putting the help text in code like this instead of a comment allows one to expand $0 so that the command name in the help text always matches the filename and path used in the invocation.
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...
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-s...
- Common shell script mistakes: http://www.pixelbeat.org/programming/shell_script_mistakes.h...
- Bash Pitfalls: http://mywiki.wooledge.org/BashPitfalls
- The Bash Hackers Wiki: 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...
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!
https://twitter.com/hellsmaddy/status/1273744824835796993?s=...
Tl;dr use `shopt -s inherit_errexit`
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...
If you can live with additional dependencies, then I like the node [1] commander package, which is very readable and nice to work with in my opinion.
It also automatically generates the --help output for ./script -h[1] https://github.com/tj/commander.js/
You could
Putting the option stuck together to its value has the advantage of working nicely with brace expansion. For example, you can call `strace -p{1111,2222,3333}` to trace those 3 pids and avoid having to type `-p` 3 times.Argparse is okay (and being in stdlib makes it always-available), but it's no click. https://click.palletsprojects.com/en/7.x/
Is that really reasonable sounding to most people for parsing CLI input/output and display manpages or helptext?
The case I used it for was much more complex. What I liked about it was the easy to use API, clear documentation & examples, and readable patterns.
For simple text display, I like the solution from the article, and I learned something new about bash scripts. Also, I learned from comments you can use heredoc in bash!
A great option when you're stuck with an old crusty script that you don't want to completely rewrite in python, but do want to clean up enough so that you can call it with `-h` and remember how to use it a few months in the future.
Unfortunately, this won't help you if you're on embedded where python isn't in the base system.
https://docs.microsoft.com/en-us/powershell/module/microsoft...
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.
But at any rate my typical usage() is generally along these lines (warning watch out for expansions):
But for more concrete examples I'll often leave off the basename - for easier cut and paste.
awk '/^###/' "$0"
if [ $# -eq 0 ] || [ "$1" = "-h" ]; then help exit 1 fi
Relevant spec bits:
https://pubs.opengroup.org/onlinepubs/9699919799/utilities/t...
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.
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:
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 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: 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:I also like to feed a heredoc directly into man, which allows you to achieve nicer formatting for the help documentation. Something like this...
See encpass.sh for a working example of this -> https://github.com/plyint/encpass.sh/blob/master/encpass.shEDIT: Full example:
Yeah, any regular unix will do, for example openbsd, freebsd or any linux distribution.
That is a very strange argument to me. You find that more cumbersome than jumping around to random functions?
By having the help documentation in a function in the middle or towards the end of the file, I don't have to page down through the help documentation to get to the code that is actually doing things. If I'm really interested in the help documentation, then I'd prefer to look at the nicely formatted version output by the script (<script> --help or whatever) rather than looking in the actual script code anyway.
Admittedly, this may be more of a subjective personal preference item.
from sh import ifconfig print(ifconfig("wlan0"))
% 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.
You could do the same thing with awk instead:
Perl for example was made for problems like this.
Then eg:
(or without the redundant addressing, just:)* 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.
https://gist.github.com/ivanistheone/0454191800c9caad77a52e0...
https://samzdat.com/
https://github.com/zsh-users/zsh-completions/blob/master/zsh...
https://github.com/DaveJarvis/scrivenvar/blob/master/build-t...
When install script[0] help is requested, the following is produced:
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/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:
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/install...
[1]: https://dave.autonoma.ca/blog/2019/05/22/typesetting-markdow...