Cut out specific fields of each line, and re-puts out. Similar to awk's function

lines_cut_fields.rb

FIELD_SPLITTER = ' ' #change to '\t', ',', ':' as you need;
FIELD_CUT_INDEXS = [0] #Start from 0;

File.open(ARGV[0]).each { |line|
    fields = line.strip.split(FIELD_SPLITTER)
    cut_fields = []
    FIELD_CUT_INDEXS.each{ |index|
        field  = fields[index]
        cut_fields.push( field )
    }
    puts cut_fields.join(FIELD_SPLITTER)
}