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Re: mapfile usage


From: Alex Reed
Subject: Re: mapfile usage
Date: Wed, 4 Feb 2009 12:44:26 -0800 (PST)
User-agent: G2/1.0

On Feb 4, 2:59 pm, Stephane CHAZELAS <address@hidden>
wrote:
> 2009-02-4, 10:50(-08), Alex Reed:
>
> > Can someone please explain how 'mapfile' should be used?  I am trying:
>
> > cat file.txt | mapfile
> > for i in ${MAPFILE};do echo $i; done
>
> > and I see no output.
>
> mapfile would be run in a subshell.
>
> Try mapfile < file.txt
>
> Note that the for loop syntax above is zsh's, not bash's.
>
> In bash (and ksh from which it derives), you need:
>
> for i in "address@hidden"; do echo "$i"; done
>
> >I've tried adding the -t option to strip
> > trailing newlines.  If I use the following command:
>
> > mapfile -u file.txt
>
> > I get the error:
>
> > bash: mapfile: file.txt: invalid file descriptor specification
> > Exit 1
>
> [...]
>
> The "help mapfile" is a bit confusing here:
>
> help> mapfile: mapfile [-n count] [-O origin] [-s count] [-t] [-u fd] [-C 
> callback] [-c quantum] [array]
> help>     Read lines from a file into an array variable.
> help>
> help>     Read lines from the standard input into the array variable ARRAY, 
> or from
>
> Looks like the first "Read lines..." was not intentional.
>
> Now I wonder why a new builtin was created for that. It looks
> like the same could have been done with very few lines of bash
> code. Also the name is misleading at it suggests writing to the
> array should write to the file (as the $mapfile associative
> array in zsh), extending the "read" builtin for that would have
> seemed more natural to me.
>
> Also, it looks like it should guard against
> seq 5 | mapfile -C echo  -c0
>
> That command above cannot be interrupted with <Ctrl-C>
>
> $ seq 5 | mapfile -C echo -c1
> 1
> 2
> 3
> 4
>
> I would have expected 1,2,3,4,5 above from the "help mapfile"
> description.
>
> mapfile <&-
>
> hangs as well (tight loop as well, cannot be interrupted).
>
> --
> Stéphane

Nice.  Thank you!


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