How do I find if a string starts with another string in Ruby

Question

What the best way to find if a string starts with another in Ruby  without rails

User · Answer

Since there are several methods presented here, I wanted to figure out which one was fastest. Using Ruby 1.9.3p362:

irb(main):001:0> require 'benchmark'
=> true
irb(main):002:0> Benchmark.realtime { 1.upto(10000000) { "foobar"[/\Afoo/] }}
=> 12.477248
irb(main):003:0> Benchmark.realtime { 1.upto(10000000) { "foobar" =~ /\Afoo/ }}
=> 9.593959
irb(main):004:0> Benchmark.realtime { 1.upto(10000000) { "foobar"["foo"] }}
=> 9.086909
irb(main):005:0> Benchmark.realtime { 1.upto(10000000) { "foobar".start_with?("foo") }}
=> 6.973697

So it looks like start_with? ist the fastest of the bunch.

Updated results with Ruby 2.2.2p95 and a newer machine:

require 'benchmark'
Benchmark.bm do |x|
  x.report('regex[]')    { 10000000.times { "foobar"[/\Afoo/] }}
  x.report('regex')      { 10000000.times { "foobar" =~ /\Afoo/ }}
  x.report('[]')         { 10000000.times { "foobar"["foo"] }}
  x.report('start_with') { 10000000.times { "foobar".start_with?("foo") }}
end

            user       system     total       real
regex[]     4.020000   0.000000   4.020000 (  4.024469)
regex       3.160000   0.000000   3.160000 (  3.159543)
[]          2.930000   0.000000   2.930000 (  2.931889)
start_with  2.010000   0.000000   2.010000 (  2.008162)

User · Answer

puts  abcdefg  start with   abc       gt  true    edit  This is something I didn t know before this question  start with takes multiple arguments    abcdefg  start with    xyz    opq    ab

User · Answer

The method mentioned by steenslag is terse  and given the scope of the question it should be considered the correct answer  However it is also worth knowing that this can be achieved with a regular expression  which if you aren t already familiar with in Ruby  is an important skill to learn    Have a play with Rubular  http   rubular com   But in this case  the following ruby statement will return true if the string on the left starts with  abc   The  A in the regex literal on the right means  the beginning of the string   Have a play with rubular - it will become clear how things work    abcdefg        Aabc

User · Answer

I like  if   string    str

[ruby] How do I find if a string starts with another string in Ruby?

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