Shell Scripting Convert Uppercase to Lowercase nixCraft. C program to convert uppercase to lowercase using isupper and tolower function. Function isupper check whether the passed character is uppercase letter or not. It returns a non zero value(true) for uppercase otherwise zero(false). Changing characters to uppercase or lowercase can be done easily with this tool by simply adding one or more of the following to your substitution stringHow to convert 5th column to lower case in comma delimited file. In this article I will tell you how I converted Uppercase text into lowercase without re-typing it all.Convert upper case text to various text cases. In this example, I will try to demonstrate how you can quickly do the same. Uppercase or Lowercase Text Tool.