How to read null terminated strings in pairs using bash

Question

Let say, have a command genpairs which generates null-terminated strings.

key1 \0 val1 \0 key2 \0 val2 \0

Want read the above input into bash variables in pairs. The following not works for me:

genpairs() { #for the demo
    printf "%d\0x\0" 1
    printf "%d\0y\0" 2
    printf "%d\0z\0" 3
}
#the above generates 1  \0   x  \0   2  \0   y  \0   3  \0   z  \0 etc...
while IFS= read -r -d '' key val; do
        echo "key:[$key] val:[$val]"
done < <(genpairs)

prints

key:[1] val:[]
key:[x] val:[]
key:[2] val:[]
key:[y] val:[]
key:[3] val:[]
key:[z] val:[]

e.g. the read somewhat doesn't split on the $'\0' into two variables.

The wanted output:

key:[1] val:[x]
key:[2] val:[y]
key:[3] val:[z]

How to read null-terminated input into multiple variables?

EDITED the OP's question - added a better demo - x y z

I can solve it as:

n=0
while IFS= read -r -d '' inp; do
        if (( n % 2 ))
        then
                val="$inp"
                echo "key:[$key] val:[$val]"
        else
                key="$inp"
        fi
        let n++
done < <(genpairs)

This prints the

key:[1] val:[x]
key:[2] val:[y]
key:[3] val:[z]

but it looks to me really terrible solution...

gniourf_gniourf · Accepted Answer · 2017-04-09 10:23:52Z

5

Just use two read statements:

while IFS= read -r -d '' key && IFS= read -r -d '' val; do
    echo "key:[$key] val:[$val]"
done < <(genpairs)

Using Bash≥4.4, you can also use mapfile with its -d switch:

while mapfile -n 2 -d '' ary && ((${#ary[@]}>=2)); do
    echo "key:[${ary[0]}] val:[${ary[1]}]"
done < <(genpairs)

edited Apr 9, 2017 at 10:23

answered Apr 9, 2017 at 10:20

gniourf_gniourf

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1 Comment

cajwine Over a year ago

WHY I need ask for such simple solutions... :( Feels stupid. Thanx a lot!!!

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