$ expr substr 00001234 3 4; echo $? 0012 0 $ expr substr 1234 1 2; echo $? 12 0
$ expr substr 00001234 1 2; echo $? 00 1 $ expr substr 00001234 1 4; echo $? 0000 1 $ expr substr 00001234 1 5; echo $? 00001 0
$ expr substr 00001234 3 4; echo $? 0012 0 $ expr substr 1234 1 2; echo $? 12 0
$ expr substr 00001234 1 2; echo $? 00 1 $ expr substr 00001234 1 4; echo $? 0000 1 $ expr substr 00001234 1 5; echo $? 00001 0