Shell Programming and Scripting

awk -F'[^0-9]*' '$0=$NF _?$NF _:$(NF-1) _' infile

awk -F'[^0-9]*' '$0=$NF?$NF:$(NF-1)' file

a 0
0 c

awk -F'[^0-9]*' '$0=$NF _?$NF _:$(NF-1)_' infile

$ echo abc 123 def 456ghi | sed 's/.* \([0-9]\{1,\}\)[^0-9]*/\1/'
456
$ echo abc 123 def 456ghi | tr -d [:alpha:] | awk '{print $NF}'
456
$ echo abc 123 def 456ghi | awk -F'[^0-9]*' '$0=$NF _?$NF _:$(NF-1)_'
456

#!/bin/sh

while IFS= read -r line; do
    set $line
    number=
    for word; do
        case $word in
            *[!0-9]*) continue;;
                   *) number=$word;;
        esac
    done
    echo $number
done