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.)

Terry M. 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).

On 10/03/2010 07:19 PM, Terry M. 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.)

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

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

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

js

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

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

seems to work too.

js

On Sun, Oct 3, 2010 at 9:19 PM, Terry M. [email protected]
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/.

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 Mon, Oct 4, 2010 at 4:19 AM, Terry M. [email protected]
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):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.

Terry M. 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”

“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!

John S. wrote:

Terry M. 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, ‘’)

On Oct 3, 9:19 pm, Terry M. [email protected] 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/.

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

Adam P. 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

On 4 October 2010 04:19, Terry M. [email protected] 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.

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

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

On Thu, Oct 7, 2010 at 7:44 AM, Terry M. [email protected]
wrote:

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.

Benoit D. wrote:

On 4 October 2010 04:19, Terry M. [email protected] 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.

On Thu, Oct 7, 2010 at 12:00 PM, Josh C. [email protected]
wrote:

are on.)
1.8.7 (patchlevel 302). Possibly not the most efficient (requires entire

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

Yep, that’s what I tested.

Jesus.

2010/10/7 Jesús Gabriel y Galán [email protected]

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 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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