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To: zsh-users@zsh.org
From: Anssi Saari <as@sci.fi>
Subject: Confused about splitting
Date: Sun, 31 Mar 2019 12:06:16 +0300
Organization: An impatient and LOUD arachnid
Message-ID: <vg3k1gf4dmf.fsf@coffee.modeemi.fi>
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I have a simple script which uses awk to assign and split a line from a
file to a zsh array. Simplified, just this:

foofunc () {
	if [[ $# -ge 1 ]]
	then
		if=$1 
	else
		if=eno1
	fi
	first=(`awk /$if/ /proc/net/dev`)

	echo $first
	echo length of first is $#first
}

Obvious and works, it prints out currently with parameter eno1 this:

eno1: 44977581223 33469291 0 139 0 0 0 57718 12574512832 21508919 0 0 0 0 0 0
length of first is 17

/proc/net/dev currently contains
Inter-|   Receive                                                |  Transmit
 face |bytes    packets errs drop fifo frame compressed multicast|bytes    packets errs drop fifo colls carrier compressed
    lo: 990081491  293912    0    0    0     0          0         0 990081491  293912    0    0    0     0       0          0
  eno1: 44978021588 33472121    0  139    0     0          0     57964 12575022205 21512486    0    0    0     0       0          0

But wanting to not call awk I ran into trouble.

If I set shwordsplit, no problem:

foofunc2 () {
	if [[ $# -ge 1 ]]
	then
		if=$1 
	else
		if=eno1
	fi
	setopt shwordsplit
	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 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.

This is with zsh 5.3.1 on Debian.