A filename should not contain any of the characters shown below. Why? They have special meaning to the shell. Technically speaking, you can use them in the composition of a filename, but you might have a difficult time accessing or deleting them in the future.
Characters not recommended in the composition of a filename.
, ! @ # $ % ^ & * ( ) - + [ ] { } < > ? ; ' " | \ / ~ ` : "space"
Recommended characters
_ 0-9 a-z A-Z .
Acceptable filenames
ABC.txt
_this_is_good
amc.txt
123.txt