The entry will be a string containing the desired permission (always complete) and the file name, ex: 'rwxrwxrwx' e 'arquivo.txt'

I'd suggest "The input will be two strings, containing the desired permissions ( always complete ) and the filename, eg. ( "rwxrwxrwx", "name.ext" )". ( Don't get hung up on specific strings. Though "arquivo" may not read very easy in English, esp. for non-native speakers. )

Is your first language Spanish or Portuguese by any chance?

Isn't that ls -l instead of ls -a ?

Also, I'd suggest showing an x somewhere. Some people may not know about UNIX inode permissions and not know what values are possible.

ETA: Oh, I overlooked the massive picture right under that that has the x in it. It's probably not that crucial. :P