I want to deal with the command line input in Ruby:
> cat input.txt | myprog.rb
> myprog.rb < input.txt
> myprog.rb arg1 arg2 arg3 ...
What is the best way to do it? In particular I want to deal with blank STDIN, and I hope for an elegant solution.
#!/usr/bin/env ruby
STDIN.read.split("\n").each do |a|
puts a
end
ARGV.each do |b|
puts b
end
Answer
Following are some things I found in my collection of obscure Ruby.
So, in Ruby, a simple no-bells implementation of the Unix command cat would be:
#!/usr/bin/env ruby
puts ARGF.read
ARGF is your friend when it comes to input; it is a virtual file that gets all input from named files or all from STDIN.
ARGF.each_with_index do |line, idx|
print ARGF.filename, ":", idx, ";", line
end
# print all the lines in every file passed via command line that contains login
ARGF.each do |line|
puts line if line =~ /login/
end
Thank goodness we didn’t get the diamond operator in Ruby, but we did get ARGF as a replacement. Though obscure, it actually turns out to be useful. Consider this program, which prepends copyright headers in-place (thanks to another Perlism, -i) to every file mentioned on the command-line:
#!/usr/bin/env ruby -i
Header = DATA.read
ARGF.each_line do |e|
puts Header if ARGF.pos - e.length == 0
puts e
end
__END__
#--
# Copyright (C) 2007 Fancypants, Inc.
#++
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