Ruby special variables

There is a collection of special variables whose names consist of a dollar sign ($) followed by a single character. For example, $$ contains the process id of the ruby interpreter, and is read-only. $ global variable @ instance variable [a-z] or _ local variable [A-Z] constant Here are the major system variables: $! latest error message $@ location of error $_ string last read by gets $. line number last read by interpreter $& string last matched by regexp $~ the last regexp match, as an array of subexpressions $n the nth subexpression in the last match (same as $~[n]) $= case-insensitivity flag $/ input record separator $\ output record separator $0 the name of the ruby script file $* the command line arguments $$ interpreter's process ID $? exit status of last executed child process In the above, $_ and $~ have local scope. Their names suggest they should be global, but they are much more useful this way, and there are historical reasons for using these names.