This one took a little bit of trial and error, but I finally got the flag to print out to the console with a simple operation. See photo:
I simply read the content of flag.txt by using command substitution to bypass the restrictions put on the challenge. I basically used eval location_of_flag but instantly redirected the output to console. < was not one of the restricted characters. 😁
Flag!
FLAG-a78i8TFD60z3825292rJ9JK12gIyVI5P