Question

I am a Java developer, and I have been given Ruby code to understand and later to work on.

I went through the Ruby tutorials on tutorialspoint.com but I can’t figure out what $_[0] is.

It is being assigned to a variable in the code, and it is definitely not a command-line argument because I wrote code to test that and it failed.
So, can anyone say what the significance of it is?

Answer 1

It’s one of the magic variables.

$_ holds value of the last line read from standard input. $_[0] is, therefore, first symbol of that string.

See English.rb for more magic variables

# The last line read by <tt>Kernel.gets</tt> or
# <tt>Kernel.readline</tt>. Many string-related functions in the
# +Kernel+ module operate on <tt>$_</tt> by default. The variable is
# local to the current scope. Thread local.
alias $LAST_READ_LINE          $_