c# - Create validation for CSV and Text file only (case insenstive) -

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i wants upload file extension .csv , .txt , case insensitive.

for example .csv, .csv, .csv, .txt, .txt , .txt ...

i using one

(?i)[.](csv|txt)

but not work when extension case-sensitive.

this regex in both client side , server side validation:

^.*\.([cc][ss][vv]|[tt][xx][tt]??)$

if want atleast 1 character name (before .txt or .csv) following help:

^.+\.([cc][ss][vv]|[tt][xx][tt]??)$

Brande