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Use long flags when scripting

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Re: Use long flags when scripting

#41

Post by npsimons »

While it is generally a good idea to write readable code, it is also true that long flags are not universally supported, and the short flags don't always have the same meanings (or even exist!) across different systems.

This is an interesting conundrum. As has been pointed out, POSIX specifies standard options (which are all short):

http://news.ycombinator.com/item?id=5165058

But these are not universally supported:

http://unixhelp.ed.ac.uk/CGI/man-cgi?ps

What to do? My proposal: do what we do in the C/C++ world when presented with portability problems: abstract it away. POSIX sh supports functions, which can be named appropriately for readability, while calling the proper arguments and commands for different platforms. To avoid unnecessary duplication of platform/argument detection, setup could be done in a function called before anything else to create variables with the appropriate command names and arguments.

This may all seem too involved, but realize that we are talking about creating robust software that is to be maintained, so applying proper software engineering principles seems appropriate.

Re: Use long flags when scripting

#42

Post by ralph »

This is very bad advice. I won't thank you for making me check GNU grep's --ignore-case is precisely the same as the very well-known, POSIX'd, -i. And ditto for all the other verbiage that clutter and obfuscate the script's intent.

Short options should be used where they're the more typically known and standardised. Long options are for the unusual.

    grep -iv
    sed -n
    tr -dc
    awk -f
    ls -tr
    comm -23
    tail -n

Re: Use long flags when scripting

#43

Post by logn »

eli wrote: post #40
ralph wrote: post #35

Earlier quoted context omitted.

No, that's wrong, a reader that knows his onions, e.g. me, will be puzzled as to what the writer's intent was and spend time investigating if there is an error before deciding the writer needs to spend more time studying his onions.

I think the goal should be clarity, not conservation of characters. And I think the escaped dot is clearer (the author's intent is obviously to include a dot in the range). I do think it's funny that you said "There isn't and shouldn't be any hard fast rule for this" and then one comment later said my approach is "wrong" :) (EDIT: oops, that wasn't you -- Sorry!)

It's only clear for people who don't really understand regexes. For people with knowledge of them, it's more ambiguous as to whether a slash is being matched or used to escape. It reminds me of commenting the end of your for loops, } //end for ... it's clear for people who come from Python and don't know Java but that's not who we should be helping.

Re: Use long flags when scripting

#44

Post by 6ren »

eli wrote: post #40
ralph wrote: post #35

Earlier quoted context omitted.

No, that's wrong, a reader that knows his onions, e.g. me, will be puzzled as to what the writer's intent was and spend time investigating if there is an error before deciding the writer needs to spend more time studying his onions.

I think the goal should be clarity, not conservation of characters. And I think the escaped dot is clearer (the author's intent is obviously to include a dot in the range). I do think it's funny that you said "There isn't and shouldn't be any hard fast rule for this" and then one comment later said my approach is "wrong" :) (EDIT: oops, that wasn't you -- Sorry!)

It seems that statement wasn't a hard and fast rule. ba dum tish I think everyone should do what they want, including telling others what to do, hypocritically.

I prefer not to escape dots in char classes, because escapes make it less readable for me. I know this involves a more complex rule, for where one need not escape, but somehow my mind easily treats character classes as a special case region.

Re: Use long flags when scripting

#45

Post by ralph »

eli wrote: post #40
ralph wrote: post #35

Earlier quoted context omitted.

No, that's wrong, a reader that knows his onions, e.g. me, will be puzzled as to what the writer's intent was and spend time investigating if there is an error before deciding the writer needs to spend more time studying his onions.

I think the goal should be clarity, not conservation of characters. And I think the escaped dot is clearer (the author's intent is obviously to include a dot in the range). I do think it's funny that you said "There isn't and shouldn't be any hard fast rule for this" and then one comment later said my approach is "wrong" :) (EDIT: oops, that wasn't you -- Sorry!)

> you said "There isn't and shouldn't be any hard fast rule for this"

No I did not. You're confused as that was someone else. :-)

Do not needlessly escape. Only escape what that flavour of syntax needs you to do. What you may think is a needless escape may actually give different behaviour.

    $ sed 's/[x\.]/y/g'

Re: Use long flags when scripting

#46

Post by webreac »

npsimons wrote: post #41

While it is generally a good idea to write readable code, it is also true that long flags are not universally supported, and the short flags don't always have the same meanings (or even exist!) across different systems. This is an interesting conundrum. As has been pointed out, POSIX specifies standard options (which are all short): http://news.ycombinator.com/item?id=5165058 But these are not universally supported:…

I think you fail on two software engineering principles:

* http://en.wikipedia.org/wiki/KISS_principle

* you should adapt the way you think about programming to the language you are using. This is shell, not Ada.

Re: Use long flags when scripting

#47

Post by jerf »

X-Istence wrote: post #28
jerf wrote: post #23

Earlier quoted context omitted.

It's always a cost/benefits analysis. I think for a lot of us, the cost/benefit goes something like this: "Will I ever have to read and modify this script again? Effectively-100% likely. Will this script ever run anywhere that I don't have the GNU toolchain? Effectively-0% likely." It's a no-brainer at that point. If you can't say that second part honestly, reconsider, but a lot of us can.

And now porting your script to non GNU such as BSD becomes a pain in the behind ... whereas before maybe only one or two commands would have had to change, now it will be most if not all.

When I mentioned "GNU", I think it sort of implied that I am aware of the existence of non-GNU toolchains.

I really am not worried about that in my world. The dependencies on Linux go a great deal deeper than the GNU toolchain. YMMV.

Re: Use long flags when scripting

#48

Post by Wilya »

njharman wrote: post #39
lamby wrote: post #27

Earlier quoted context omitted.

> Will this script ever run anywhere that I don't have the GNU toolchain? Effectively-0% likely. Not really. A lot of stuff broke when /bin/sh moved to a POSIX-compatibile shell rather than Bash.

No a lot of stuff broke because people depended on implicit rather than being explicit. #!/bin/bash

  wilya@home $ /bin/bash
  zsh: no such file or directory: /bin/bash
  wilya@home $ which bash
  /usr/local/bin/bash
(Yes, I'm annoyed when I see #!/bin/bash, especially on scripts which are otherwise basic enough to be portable everywhere)

Re: Use long flags when scripting

#49

Post by ralph »

StavrosK wrote: post #30
eli wrote: post #19

Earlier quoted context omitted.

IMHO, if your intent is to capture a literal dot then you should escape it even if, based on the context, you don't have to.

I agree with this. Regexps in general encourage a bit of "if unsure, escape".

Then you could be introducing errors into your regexps. \x doesn't mean a plain x instead of the metacharacter x in all cases. Don't ship code you don't at least think you understand.

Re: Use long flags when scripting

#50

Post by jcurbo »

webreac wrote: post #46
npsimons wrote: post #41

While it is generally a good idea to write readable code, it is also true that long flags are not universally supported, and the short flags don't always have the same meanings (or even exist!) across different systems. This is an interesting conundrum. As has been pointed out, POSIX specifies standard options (which are all short): http://news.ycombinator.com/item?id=5165058 But these are not universally supported:…

I think you fail on two software engineering principles: * http://en.wikipedia.org/wiki/KISS_principle * you should adapt the way you think about programming to the language you are using. This is shell, not Ada.

Sure, but what's wrong with his approach? POSIX sh supports all the things you need to do 'if GNU grep run this, else if BSD grep run that' - functions, case statements, conditionals. He's not talking about building up major libraries in shell, just wrapping the invocations in functions based on the environment you're in.
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