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From: Daniel Shahaf <d.s@daniel.shahaf.name>
To: Anssi Saari <as@sci.fi>
Cc: zsh-users@zsh.org
Subject: Re: Confused about splitting
Date: Sun, 31 Mar 2019 12:58:13 +0000	[thread overview]
Message-ID: <20190331125813.pd45aqx4bvdjnrgr@tarpaulin.shahaf.local2> (raw)
In-Reply-To: <vg3k1gf4dmf.fsf@coffee.modeemi.fi>

Anssi Saari wrote on Sun, Mar 31, 2019 at 12:06:16 +0300:
> foofunc2 () {
> 	setopt shwordsplit

This should have been «setopt localoptions shwordsplit».

⋮
> }

> But what if I don't want to set shwordsplit? I came up with
> 
> foofunc3 () {
> 	if [[ $# -ge 1 ]]
> 	then
> 		if=$1 
> 	else
> 		if=eno1
> 	fi
> 	while read g
> 	do
> 	    if [[ $g =~ $if ]]
> 	    then
> 		first=${=g}
> 		break
> 	    fi
> 	done < /proc/net/dev
> 
> 	echo $first
> 	echo length of first is $#first
> }
> 
> But this splits each character into an array element. I don't understand
> this behavior at all. As I understand it, = in the assignment to $first
> is supposed to turn shwordsplit on temporarily but it really doesn't
> seem to. IFS is not set so field separator should be default, meaning
> whitespace.

«${=g}» does split the value of the parameter 'g'; you can see that with
«printf '[%s]' ${=g}».  Then, that intermediate result — an array of words — is
assigned to the parameter 'first' scalarly, so the value of $first is set to be
the words of the array joined by spaces as a single string.  That's why «echo
$first» has the right output.  The «echo $#first» line prints the length of the
string "$first" in characters, because that's what the «$#foo» syntax does when
foo is a scalar.

The fix is to add back the parentheses to make the assignment an array
assignment: «first=( ${=g} )».

Furthermore, note that if $first had been an array of one-character strings,
the output of the first 'echo' would have been incorrect: compare «echo $foo»
(echos a string) and «echo ${(s::)foo}» (echos an array of one-character
strings).

Cheers,

Daniel

  reply	other threads:[~2019-03-31 12:59 UTC|newest]

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-03-31  9:06 Anssi Saari
2019-03-31 12:58 ` Daniel Shahaf [this message]
2019-03-31 17:56   ` Anssi Saari
2019-03-31 13:12 ` Daniel Shahaf
2019-04-01  9:07   ` Anssi Saari

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