如何从Ruby中的String获取第一行？

Question

我在Ruby中有一个字符串变量,如下所示:

puts $varString.class
puts "##########"
puts $varString

上面代码的输出是:

String 
##########
my::FIrst::Line
 this id second line 
 sjdf kjsdfh jsdf 
 djsf sdk fxdj

我只需要从字符串变量中获取第一行(例如my::FIrst::Line).我怎么才能得到它？

Answer 1

# Ruby >= 1.8.7
$varString.lines.first
# => "my::FIrst::Line"

# Ruby < 1.8.7
$varString.split("\n").first
# => "my::FIrst::Line"

作为旁注,请避免使用全局($符号)变量.

Answer 2

$varString.lines.first

或者,如果您想在结果字符串中删除最终换行符:

$varString.lines.first.chomp

Answer 3

first_line = str[/.*/]

就内存分配和性能而言，该解决方案似乎是最有效的解决方案。

这使用的str[regexp]形式，请参阅https://ruby-doc.org/core-2.6.5/String.html#method-i-5B-5D

基准代码：

require 'stringio'
require 'benchmark/ips'
require 'benchmark/memory'

str = "test\n" * 100

Benchmark.ips do |x|
  x.report('regex') { str[/.*/] }
  x.report('index') { str[0..(str.index("\n") || -1)] }
  x.report('stringio') { StringIO.open(str, &:readline) }
  x.report('each_line') { str.each_line.first.chomp }
  x.report('lines') { str.lines.first }
  x.report('split') { str.split("\n").first }
  x.compare!
end

Benchmark.memory do |x|
  x.report('regex') { str[/.*/] }
  x.report('index') { str[0..(str.index("\n") || -1)] }
  x.report('stringio') { StringIO.open(str, &:readline) }
  x.report('each_line') { str.each_line.first.chomp }
  x.report('lines') { str.lines.first }
  x.report('split') { str.split("\n").first }
  x.compare!
end

基准测试结果：

Comparison:
               regex:  5099725.8 i/s
               index:  4968096.7 i/s - 1.03x  slower
            stringio:  3001260.8 i/s - 1.70x  slower
           each_line:  2330869.5 i/s - 2.19x  slower
               lines:   187918.5 i/s - 27.14x  slower
               split:   182865.6 i/s - 27.89x  slower

Comparison:
               regex:         40 allocated
               index:        120 allocated - 3.00x more
            stringio:        120 allocated - 3.00x more
           each_line:        208 allocated - 5.20x more
               lines:       5064 allocated - 126.60x more
               split:       5104 allocated - 127.60x more