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Re: Strange compgen behaviour


From: Chet Ramey
Subject: Re: Strange compgen behaviour
Date: Fri, 25 Sep 2009 13:45:49 -0400
User-agent: Thunderbird 2.0.0.23 (Macintosh/20090812)

Bernd Eggink wrote:
> Chet Ramey schrieb:
>>> Hm, compgen appears to behave strange if words contain whitespace. 
>>
>> Well, it splits the argument to -W on $IFS as documented.  What other
>> strange behavior do you see? 
> 
> For example, this:
> 
>     function _aha
>     {
>         local list="a b:c d:e f"
>         COMPREPLY=($(IFS=: compgen -W "$list"))
>     }
> 
>     complete -F _aha aha
> 
> Typing aha <Tab> cycles through 6 items a, b, c, d, e, f, whereas I
> would expect 3 items 'a b', 'c d', 'e f'. It looks like compgen splits
> the argument to -W on $IFS _and_ whitespace. Or am I missing something?

I don't think you're considering the interaction between compgen,
command substitution, and compound array assignment.

I'll use the assignment to `list' you used above for the explanation.

compgen performs word splitting using $IFS and then outputs the results,
one word per line:

$ IFS=: compgen -W "$list"
a b
c d
e f

Command substitution takes that, chops off the last newline, and, since
it's unquoted, performs word splitting using $IFS on the result:

$ recho $(IFS=: compgen -W "$list")
argv[1] = <a>
argv[2] = <b>
argv[3] = <c>
argv[4] = <d>
argv[5] = <e>
argv[6] = <f>

If you want to preserve the embedded newlines, you have to quote the
expansion (but see below):

$ recho "$(IFS=: compgen -W "$list")"
argv[1] = <a b^Jc d^Je f>

When performing compound array assignments, though, the words between
the parens undergo all the shell word expansions, including word splitting:

$ COMPREPLY=( $(IFS=: compgen -W "$list") )
$ recho "address@hidden"
argv[1] = <a>
argv[2] = <b>
argv[3] = <c>
argv[4] = <d>
argv[5] = <e>
argv[6] = <f>

So you can split on just the embedded newlines by setting $IFS:

$ oifs="$IFS"
$ IFS=$'\n' COMPREPLY=( $(IFS=: compgen -W "$list") )
$ IFS="$oifs"
$ recho "address@hidden"
argv[1] = <a b>
argv[2] = <c d>
argv[3] = <e f>

Remember to save and restore $IFS, though, since the assignment to it
preceding the assignment to COMPREPLY will persist.

Chet
-- 
``The lyf so short, the craft so long to lerne.'' - Chaucer
                 ``Ars longa, vita brevis'' - Hippocrates
Chet Ramey, ITS, CWRU    address@hidden    http://cnswww.cns.cwru.edu/~chet/




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