Case-insensitive Glob on zsh/bash
ZSH:
$ unsetopt CASE_GLOBOr, if you don't want to enable case-insensitive globbing in general, you can activate it for only the varying part:
$ print -l (#i)(somelongstring)*This will match any file that starts with "somelongstring" (in any combination of lower/upper case). The case-insensitive flag applies for everything between the parentheses and can be used multiple times. Read the manual zshexpn(1) for more information.
UPDATEAlmost forgot, you have to enable extendend globbing for this to work:
setopt extendedglob