powershell - How to insert 0 in a string -

this array :

eth1 eth12 eth5 eth11 

when string contains number between 1 , 9 want add 0 before, obtain array :

eth01 eth12 eth05 eth11 

how can achieve this? don't know how modify string :/

thanks

like this:

$if = 'eth1', 'eth12', 'eth5', 'eth11' $if -replace '(\d+)(\d)$', '${1}0$2'