Bash [ -z hello ]

https://duckduckgo.com/?q=bash+%5B+-z+hello+%5D

by ca98am79 • 12 years ago

174 59 12 years ago

Nice! It's too bad that this doesn't actually evaluate the expression in a sandbox, but nonetheless it's a very handy syntax guide.

It'd be nice to see option descriptions extracted from manpages: searching for "df -h" could then produce:

       -h, --human-readable
              print sizes in human readable format (e.g., 1K 234M 2G)

jmakeig• 12 years ago

http://explainshell.com is what you're looking for.

JoshTriplett2• 12 years ago

I'm aware of it; I'd love to see that functionality integrated into DDG.

Alupis2• 12 years ago

What a great resource! I did not know about this before today!

voltagex_2• 12 years ago

I wonder if the developer of explainshell is reading. It looks like development has stalled. It's a really nice idea and could serve as a powerful backend for DDG.

frabcus• 12 years ago

I note that queries like https://duckduckgo.com/?q=man+df put in a box from LinuxCommand.org

Nyubis• 12 years ago

This is pretty awesome, but I don't know if people often phrase their queries like that, and I'm not sure whether it's worth it to start phrasing it like this. It doesn't seem to support more complex bash queries, so I'm not really sure how often this will be used.

mattdanger• 12 years ago

[ is part of Bash syntax

frou_dh2• 12 years ago

...and perhaps surprisingly also a program sitting on disk.

    $ type [
    [ is a shell builtin
    $ [ 1 -gt 0
    bash: [: missing `]'

    $ whereis [
    /bin/[
    $ /bin/[ 1 -gt 0
    # success

embolalia• 12 years ago

Nooo! Mistake #0 about shell scripting is thinking [ is syntax. It makes it way more weird and inexplicable. [ is a command, just like any other. That's why there needs to be a space between it and the next thing, and why you have to use weird looking flags and such. This is why I prefer the command `test`. It does the same thing as `[`, but is more obviously a command. And when you see it as a command, it's obvious that any command can be used in an if directly; if is just checking the exit code. (Whenever I see someone doing `if [ $? -ne 0 ]`, it makes me cry.)

the_french• 12 years ago

It seems like DDG is positioning itself to become WolframAlpha for tech. Hopefully, this will allow it to better catch the exact market segment that would be wary of search engine tracking (educated tech-savvy people).

pornel• 12 years ago

More please! e.g.

     bash $?

is not explained.

jagtalon• 12 years ago

If you're interested, you can add that in to https://github.com/duckduckgo/zeroclickinfo-goodies/blob/mas... since it's open source.

Crisco• 12 years ago

I've been reading through some of those goodies, and they all seem pretty cool, but I'm wondering how secure using the 4 word random passphrase generator[0] would be...

[0] https://github.com/duckduckgo/zeroclickinfo-goodies/blob/mas...

vacri2• 12 years ago

I'm always finding another bash magic variable. '$?' is 'exit code of last command'. Last week I found '$-', which tells you which flags are currently set (set -x, set -e type of thing).

FreeFull• 12 years ago

They are all listed in the man page, thankfully.

imacomputer2• 12 years ago

"results to true if the length of 'hello' is zero." I'm glad they cleared that up. Otherwise, I might have assumed that there was no case where 'hello' had a length of zero. Joking aside, it is a useful syntax guide.

chx• 12 years ago

And yet, the top search result is tldp. This is what #bash on freenode has to say about that site:

The infamous "Advanced" Bash Scripting Guide should be avoided unless you know how to filter out the junk. It will teach you to write bugs, not scripts. In that light, the BashGuide was written: http://mywiki.wooledge.org/BashGuide

Now, that site is on the second "page" of the search results.

zhemao• 12 years ago

To be fair, searching it in Google also gives TLDP pages as the top results. I think TLDP just has better SEO.

n0rm• 12 years ago

It just has more nodes pointing to its links.

That's the danger behind PageRank. If something false is popular enough, it will replace fact.

mhurron• 12 years ago

Do they have examples of how it's bad as opposed to simply declaring it bad?

js23• 12 years ago

Well for example, I just skimmed through it and I don't see an explanation of quoting, probably one of the first things I would want to explain, around the time variables are explained. It also has examples like this:

        #!/bin/bash
        for i in $( ls ); do
            echo item: $i
        done

which both uselessly calls ls (you may as well just use a glob) and doesn't work as intended if there are filenames with spaces in the directory.

You also have:

        #!/bin/bash
        for i in `seq 1 10`;
        do
                echo $i
        done

Why is it using backticks here instead of $() as in thr former example? Also, no mention that seq is not available on some systems. And, you should be using bash's sequence expression[1] anyway (added in bash 4.x), so the guide is likely out of date.

1. http://www.gnu.org/software/bash/manual/bashref.html#Brace-E...

skywhopper• 12 years ago

The TLDP bash guide is full of a range of submitted examples that run the gamut of good and bad practices. That said, it's still one of the better resources out there, and I have the reference page bookmarked. But this is Bash we're talking about, "best" practice is a relative term.

voltagex_2• 12 years ago

I'd like that too.

At this stage it's no better than a meme: https://groups.google.com/d/msg/comp.os.linux.misc/w0bcKoEye...

I know that if you mention the TLDP stuff in #bash you get yelled at, though.

fyrabanks• 12 years ago

I learned bash using tldp years ago, never had any major issues.

est• 12 years ago

Damn, should draw FSA fors RegExps.

Like this

https://www.debuggex.com/r/IC3q9sEdkKjhuLWU

And explains it like this

http://regex101.com/

wicket2• 12 years ago

There should a dollar sign before hello, e.g.:

bash [ -z $hello ]

...or is that a bashism that I'm not aware of? If so, that's just horrible.

Personally, I prefer to write portable shell scripts. Entering "!posix test" into DuckDuckGo to obtain the man page for "test" yields far more meaningful information for the same problem.

simias• 12 years ago

[ -z hello ] is perfectly fine, but hello is not a variable, it's the string "hello". It will always return false. ddg doesn't seem to evaluate the command, just explicit it.

wicket2• 12 years ago

It will always return false.

Exactly! It's not the best of examples really, is it?

d0m• 12 years ago

As an aside, I think the new design is perfect. Good job on iterating on the feedback!

Bash [ -z hello ]

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