Save only first line from string?

Hi. What's the most simple and elegant way to remove all the contents of
a String except for the first line? (Assume string consist of one line,
multiple lines, or no lines, and assume that we don't know which OS we
are on.)

···

--
Posted via http://www.ruby-forum.com/.

Assuming you mean to actually modify the string, you could do this:

irb(main):001:0> "a string\nwith multiple\nlines".gsub! /\A(.*?)$(.*)\z/m, '\1'
=> "a string"
irb(main):002:0> "a string with one line".gsub! /\A(.*?)$(.*)\z/m, '\1'
=> "a string with one line"
irb(main):003:0> "".gsub! /\A(.*?)$(.*)\z/m, '\1'
=> ""

If you don't need to modify the string:

irb(main):004:0> "a string\nwith multiple\nlines".match(/\A.*?$/)[0]
=> "a string"
irb(main):005:0> "a string with one line".match(/\A.*?$/)[0]
=> "a string with one line"
irb(main):006:0> "".match(/\A.*?$/)[0]
=> ""

-Justin

···

On 10/03/2010 07:19 PM, Terry Michaels wrote:

Hi. What's the most simple and elegant way to remove all the contents of
a String except for the first line? (Assume string consist of one line,
multiple lines, or no lines, and assume that we don't know which OS we
are on.)

Terry Michaels wrote:

Hi. What's the most simple and elegant way to remove all the contents of
a String except for the first line? (Assume string consist of one line,
multiple lines, or no lines, and assume that we don't know which OS we
are on.)

I don't know about the most elegant or simple way, but how about this:

string.sub!(/^(.*\n?)((?im).+)?/, '\1').chomp

Some tests:

string_1 = <<END_OF_STRING_1
hello there.
how is it going?
END_OF_STRING_1

string_2 = "hi there\n"
string_3 = "\n"
string_4 = 'hi'
string_5 = ''

regex = /^(.*\n?)((?im).+)?/

p string_1.sub!(regex, '\1').chomp # => "hello there."
p string_2.sub!(regex, '\1').chomp # => "hi there"
p string_3.sub!(regex, '\1').chomp # => ""
p string_4.sub!(regex, '\1').chomp # => "hi"
p string_5.sub!(regex, '\1').chomp # => ""

I don't think that the ^ is really needed, but I included it anyway.
Also, don't be surprised if someone finds a fault with this or comes up
with a better solution (I never figured I would be giving advice on
regexs).

···

--
Posted via http://www.ruby-forum.com/\.

require 'test/unit'

def first_line(string)
  string.gsub( /$[^\Z]*\Z/m , '' )
end

class FirstLineTest < Test::Unit::TestCase

  def test_return_empty_string_when_given_empty_string
    assert_equal "" , first_line("")
  end

  def test_returns_string_when_given_one_line_string_with_no_newline
    string = "abc def ghi"
    assert_equal string , first_line(string.dup)
  end

  def
test_returns_string_without_newline_when_given_one_line_string_with_newline
    string = "abc def ghi\n"
    assert_equal string.chomp , first_line(string.dup)
  end

  def test_returns_first_line_without_newline_when_given_multi_line_string
    string = "abc def ghi\njkl mno pqr\nstu vwx yz"
    assert_equal "abc def ghi" , first_line(string.dup)
  end

  def test_does_not_mutate_original_string
    string = "abc def ghi\njkl mno pqr\nstu vwx yz"
    first_line string
    assert_equal "abc def ghi\njkl mno pqr\nstu vwx yz" , string
  end
end

···

On Sun, Oct 3, 2010 at 9:19 PM, Terry Michaels <spare@frigidcode.com> wrote:

Hi. What's the most simple and elegant way to remove all the contents of
a String except for the first line? (Assume string consist of one line,
multiple lines, or no lines, and assume that we don't know which OS we
are on.)
--
Posted via http://www.ruby-forum.com/\.

Terry Michaels wrote:

Hi. What's the most simple and elegant way to remove all the contents of
a String except for the first line? (Assume string consist of one line,
multiple lines, or no lines, and assume that we don't know which OS we
are on.)

"a string\nwith multiple\nlines".split(/\n|\r\n/)[0]

=> "a string"

···

--
Posted via http://www.ruby-forum.com/\.

irb(main):004:0> a = "abcde\nfghwrferf\nqwerim1o34ir1"
=> "abcde\nfghwrferf\nqwerim1o34ir1"
irb(main):005:0> a.first
=> "abcde\n"
irb(main):006:0> a.first.chomp
=> "abcde"

Jesus.

···

On Mon, Oct 4, 2010 at 4:19 AM, Terry Michaels <spare@frigidcode.com> wrote:

Hi. What's the most simple and elegant way to remove all the contents of
a String except for the first line? (Assume string consist of one line,
multiple lines, or no lines, and assume that we don't know which OS we
are on.)

"a string\nwith multiple\nlines"[ /.*/ ]
    ==>"a string"

···

On Oct 3, 9:19 pm, Terry Michaels <sp...@frigidcode.com> wrote:

Hi. What's the most simple and elegant way to remove all the contents of
a String except for the first line? (Assume string consist of one line,
multiple lines, or no lines, and assume that we don't know which OS we
are on.)
--
Posted viahttp://www.ruby-forum.com/.

Probably the most elegant, with Ruby 1.9:

str = str.lines.first

add ".chomp" if you want to remove the trailing EOL.

···

On 4 October 2010 04:19, Terry Michaels <spare@frigidcode.com> wrote:

Hi. What's the most simple and elegant way to remove all the contents of
a String except for the first line? (Assume string consist of one line,
multiple lines, or no lines, and assume that we don't know which OS we
are on.)
--

irb(main):005:0> s = "multiple\nlines\n"
=> "multiple\nlines\n"
irb(main):006:0> s[/^.*$/]
=> "multiple"
irb(main):007:0> s[/^.*?$/]
=> "multiple"

Cheers

robert

···

On Mon, Oct 4, 2010 at 4:19 AM, Terry Michaels <spare@frigidcode.com> wrote:

Hi. What's the most simple and elegant way to remove all the contents of
a String except for the first line? (Assume string consist of one line,
multiple lines, or no lines, and assume that we don't know which OS we
are on.)

--
remember.guy do |as, often| as.you_can - without end
http://blog.rubybestpractices.com/

string.sub!(/^(.*\n?)((?im).+)?/, '\1').chomp

Oops, already found a problem. The chomp is not chomp! So it does not
cut the "\n" off of the string (if present). You can;t just put the ! on
the end of chomp because it returns nil if "\n" was not found.

js

···

--
Posted via http://www.ruby-forum.com/\.

John Sikora wrote:

Terry Michaels wrote:

Hi. What's the most simple and elegant way to remove all the contents of
a String except for the first line? (Assume string consist of one line,
multiple lines, or no lines, and assume that we don't know which OS we
are on.)

I don't know about the most elegant or simple way, but how about this:

string.sub!(/^(.*\n?)((?im).+)?/, '\1').chomp

Why not just this?

string.sub!(/\n.*/m, '')

Or if you are a Windows user,

string.sub!(/[\r\n].*/m, '')

···

--
Posted via http://www.ruby-forum.com/\.

"a string\nwith multiple\nlines".split(/\n|\r\n/)[0]

=> "a string"

"a string\nwith multiple\nlines".split(/\r?\n/).first

I was somewhat amazed to find not the split solution, but the rather
wild (g)sub solutions as the first responses!

···

On Mon, Oct 4, 2010 at 8:25 AM, Steel Steel <angel_steel@ymail.com> wrote:

Terry Michaels wrote:

Hi. What's the most simple and elegant way to remove all the contents of
a String except for the first line? (Assume string consist of one line,
multiple lines, or no lines, and assume that we don't know which OS we
are on.)

"a string\nwith multiple\nlines".split(/\n|\r\n/)[0]

=> "a string"
--
Posted via http://www.ruby-forum.com/\.

Benoit Daloze wrote:

···

On 4 October 2010 04:19, Terry Michaels <spare@frigidcode.com> wrote:

Hi. What's the most simple and elegant way to remove all the contents of
a String except for the first line? (Assume string consist of one line,
multiple lines, or no lines, and assume that we don't know which OS we
are on.)
--

Probably the most elegant, with Ruby 1.9:

str = str.lines.first

add ".chomp" if you want to remove the trailing EOL.

Definitely the most elegant! (Defining 'elegant' as simple, natural,
easy to read) Thanks! This seems to work fine on my system with ruby
1.8.7 (patchlevel 302). Possibly not the most efficient (requires entire
string to be split into array elements) but okay in my case.

In fairness to the others, I should have explained that I was okay with
replacing the old string with a new string.
--
Posted via http://www.ruby-forum.com/\.

Justin's looks good. I should have just let someone who knew what they
were doing answer.

js

···

--
Posted via http://www.ruby-forum.com/.

Adam Prescott wrote:

"a string\nwith multiple\nlines".split(/\n|\r\n/)[0]

=> "a string"

"a string\nwith multiple\nlines".split(/\r?\n/).first

I was somewhat amazed to find not the split solution, but the rather
wild (g)sub solutions as the first responses!

I, perhaps erroneously, thought that the OP wanted to modify the string.
If so, the split method seems somewhat inelegant, perhaps:

string = string.split(/\n|\r\n/)[0]. So I posted the sub! way instead.

js

···

--
Posted via http://www.ruby-forum.com/\.

Did my solution work for you?

str = str.first

This way you avoid the intermediate array.

Jesus.

···

On Thu, Oct 7, 2010 at 7:44 AM, Terry Michaels <spare@frigidcode.com> wrote:

Benoit Daloze wrote:

On 4 October 2010 04:19, Terry Michaels <spare@frigidcode.com> wrote:

Hi. What's the most simple and elegant way to remove all the contents of
a String except for the first line? (Assume string consist of one line,
multiple lines, or no lines, and assume that we don't know which OS we
are on.)
--

Probably the most elegant, with Ruby 1.9:

str = str.lines.first

add ".chomp" if you want to remove the trailing EOL.

Definitely the most elegant! (Defining 'elegant' as simple, natural,
easy to read) Thanks! This seems to work fine on my system with ruby
1.8.7 (patchlevel 302). Possibly not the most efficient (requires entire
string to be split into array elements) but okay in my case.

In fairness to the others, I should have explained that I was okay with
replacing the old string with a new string.

Sorry to blabber on, but I am trying to learn this myself.

string.sub!(/^(.*)\n?((?im).+)?/, '\1')

seems to work too.

js

···

--
Posted via http://www.ruby-forum.com/.

I, perhaps erroneously, thought that the OP wanted to modify the string.

Oh, yes, I missed that; I should pay more attention.

···

On Mon, Oct 4, 2010 at 3:18 PM, John Sikora <john.sikora@xtera.com> wrote:

Adam Prescott wrote:

"a string\nwith multiple\nlines".split(/\n|\r\n/)[0]

=> "a string"

"a string\nwith multiple\nlines".split(/\r?\n/).first

I was somewhat amazed to find not the split solution, but the rather
wild (g)sub solutions as the first responses!

I, perhaps erroneously, thought that the OP wanted to modify the string.
If so, the split method seems somewhat inelegant, perhaps:

string = string.split(/\n|\r\n/)[0]. So I posted the sub! way instead.

js
--
Posted via http://www.ruby-forum.com/\.

I tried it on 1.8.6, 1.8.7, 1.9.1, 1.9.2, and found that it only worked on
1.8.7

···

2010/10/7 Jesús Gabriel y Galán <jgabrielygalan@gmail.com>

On Thu, Oct 7, 2010 at 7:44 AM, Terry Michaels <spare@frigidcode.com> > wrote:
> Benoit Daloze wrote:
>> On 4 October 2010 04:19, Terry Michaels <spare@frigidcode.com> wrote:
>>> Hi. What's the most simple and elegant way to remove all the contents
of
>>> a String except for the first line? (Assume string consist of one line,
>>> multiple lines, or no lines, and assume that we don't know which OS we
>>> are on.)
>>> --
>>
>> Probably the most elegant, with Ruby 1.9:
>>
>> str = str.lines.first
>>
>> add ".chomp" if you want to remove the trailing EOL.
>
> Definitely the most elegant! (Defining 'elegant' as simple, natural,
> easy to read) Thanks! This seems to work fine on my system with ruby
> 1.8.7 (patchlevel 302). Possibly not the most efficient (requires entire
> string to be split into array elements) but okay in my case.
>
> In fairness to the others, I should have explained that I was okay with
> replacing the old string with a new string.

Did my solution work for you?

str = str.first

This way you avoid the intermediate array.

Jesus.

Jesús Gabriel y Galán wrote:

str = str.first

This way you avoid the intermediate array.

String#lines returns an Enumerator, not an Array. I haven't looked at
its implementation, but it does not necessarily process the whole string
if you only call #first.

···

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