save only first line from string?

[Terry Michaels]

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.)

 

[Justin Collins]

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.)

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

 

[John Sikora]

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).

 

[John Sikora]

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

 

[John Sikora]

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

js

 

[John Sikora]

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

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

seems to work too.

js

 

[Josh Cheek]

[Note: parts of this message were removed to make it a legal post.]

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.)

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

 

[Steel Steel]

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"

 

[Jesús Gabriel y Galán]

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):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.

 

[Brian Candler]

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, '')

 

[Adam Prescott]

"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!

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"

 

[w_a_x_man]

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"

 

[John Sikora]

"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

 

[Adam Prescott]

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

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

"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

 

[Benoit Daloze]

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.

 

[Terry Michaels]

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.

 

[Jesús Gabriel y Galán]

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.

 

[Josh Cheek]

Did my solution work for you?

str =3D str.first

This way you avoid the intermediate array.

Jesus.

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

 

[Jesús Gabriel y Galán]

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

Yep, that's what I tested.

Jesus.

 

[Andreas S.]

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.