Split a string to characters in Bash

Input string:

1234 5678

o/p required:

1
2
3
4

5
6
7
8

Using -w option of Linux fold (wrap each input line to fit in specified width)

$ echo "1234 5678" | fold -w1

Awk solution : Make field separator (FS) as NULL so that each character represents a field

$ echo "1234 5678" | awk 'BEGIN{FS=""}{for(i=1;i<=NF;i++)print $i}'

Using bash:

#!/bin/sh

str="1234 5678"
while [ -n "$str" ]
        do
                printf "%c\n" "$str"
                str=${str#?}
done

Using sed (Using & as matched string)

$ echo "1234 5678" | sed 's/[0-9 ]/&\n/g'