$ perl -wE 'say "$_m" for (1 .. 5)'
Use of uninitialized value $_m in string at -e line 1.

Use of uninitialized value $_m in string at -e line 1.

Use of uninitialized value $_m in string at -e line 1.

Use of uninitialized value $_m in string at -e line 1.

Use of uninitialized value $_m in string at -e line 1.

$ perl -wE 'say "${_}m" for (1 .. 5)'
1m
2m
3m
4m
5m
$