Bash - how to iterate over array in steps of 2?

Question

I'm wondering what's the best way to iterate over an array in steps of 2 or more in bash?

For example the following 2 approaches work, but what's the cleanest/simplest way to do this?

test_loops.sh

#!/usr/bin/env bash

function strategyOne()
{
  X=0
  for I in "$@"
  do
    X=$((X%2))
    if [ $X -eq 1 ]
    then
      B="$I"
      echo "Pair: $A,$B"
    else
      A="$I"
    fi

    X=$((X+1))
  done
}

function strategyTwo()
{
 ARG_COUNT=$#
 COUNTER=0
 while [  $COUNTER -lt $ARG_COUNT ]; do
     let COUNTER=COUNTER+1 
     A="${!COUNTER}"
     let COUNTER=COUNTER+1 
     B="${!COUNTER}"

     if [ $COUNTER -le $ARG_COUNT ]
     then
       echo "Pair: $A,$B"
     fi
 done
         
}

echo
echo "Strategy 1"
strategyOne $*

echo
echo "Strategy 2"
strategyTwo $*

Produces output like so:

$ ./test.sh a b c d e

Strategy 1
Pair: a,b
Pair: c,d

Strategy 2
Pair: a,b
Pair: c,d

Matias Barrios · Accepted Answer · 2017-09-25 17:55:47Z

9

Here you have a simple way in Bash.

#!/bin/bash

data=("Banana" "Apple" "Onion" "Peach")

for ((i=0;i< ${#data[@]} ;i+=2));
do
        echo ${data[i]}
done

Regards!

answered Sep 25, 2017 at 17:55

Matias Barrios

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Comments

h0tw1r3 · Accepted Answer · 2018-12-10 06:08:06Z

5

One more way to do this:

data=("Banana" "Apple" "Onion" "Peach")
for i in $(seq 0 2 $((${#data[@]}-1)))
do
    echo ${data[i]}
done

edited Dec 10, 2018 at 6:08

h0tw1r3

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answered Sep 26, 2017 at 9:43

Maxim Norin

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Comments

anubhava · Accepted Answer · 2017-09-25 17:54:41Z

2

You can use iterate using array index:

arr=( 1 2 3 4 5 6 7 8 9 )

for ((i=0; i<${#arr[@]}; i+=2)); do echo "${arr[i]}"; done

1
3
5
7
9

answered Sep 25, 2017 at 17:54

anubhava

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