Sams Teach Yourself Shell Programming in 24 Hours, Second Edition

Questions

1:	What are invisible files? How can they be listed with ls?
2:	Is there any difference in the output of the following commands? $ ls -a1 $ ls -1 -a $ ls -1a
3:	Which options should be specified to wc to count just the number of lines and characters in a file?
4:	Given that hw1, hw2, ch1, and ch2 are files and book and homework are directories, which of the following commands generates an error message? $ cp hw1 ch2 homework $ cp hw1 homework hw2 book $ rm hw1 homework ch1 $ rm hw2 ch2