fails:ARGF.readline reads one line of a file
fails:ARGF.readline reads all lines of a file
fails:ARGF.readline reads all lines of stdin
fails:ARGF.readline reads all lines of two files
fails:ARGF.readline sets $_ global variable with each line read
fails:ARGF.readline modifies the files when in place edit mode is on
fails:ARGF.readline modifies and backups two files when in place edit mode is on
fails:ARGF.readline raises an EOFError when reaching end of files
