Question

Suppose I have string variables like following:

s1="10$" 
s2="10$ I am a student"
s3="10$Good"
s4="10$       Nice weekend!"

As you see above, s2 and s4 have white space(s) after 10$ .

Generally, I would like to have a way to check if a string start with 10$ and have white-space(s) after 10$ . For example, The rule should find s2 and s4 in my above case. how to define such rule to check if a string start with ’10$’ and have white space(s) after?

What I mean is something like s2.RULE? should return true or false to tell if it is the matched string.

———- update ——————-

please also tell the solution if 10# is used instead of 10$

Answer 1

You can do this using Regular Expressions (Ruby has Perl-style regular expressions, to be exact).

# For ease of demonstration, I've moved your strings into an array
strings = [
  "10$",
  "10$ I am a student",
  "10$Good",
  "10$       Nice weekend!"
]

p strings.find_all { |s| s =~ /\A10\$[ \t]+/ }

The regular expression breaks down like this:

• The / at the beginning and the end tell Ruby that everything in between is part of the regular expression
• \A matches the beginning of a string
• The 10 is matched verbatim
• \$ means to match a $ verbatim. We need to escape it since $ has a special meaning in regular expressions.
• [ \t]+ means “match at least one blank and/or tab”

So this regular expressions says “Match every string that starts with 10$ followed by at least one blank or tab character”. Using the =~ you can test strings in Ruby against this expression. =~ will return a non-nil value, which evaluates to true if used in a conditional like if.

Edit: Updated white space matching as per Asmageddon’s suggestion.