If /hello/ =~line

Ruby
1

Got help with this code earlier its just checking a file for a line

Im really new to ruby ive used java and C before

just wondering what do i put in if i want to use a variable that is
holding the string eg VAR1 = “hello”

File.foreach “file.txt” do |line|
if /hello/ =~ line
puts “found it”
break
end
end

2

You can use string interpolation like you can with double quoted
strings.

var1 = “hello”

File.foreach “file.txt” do |line|
if /#{var1}/ =~ line
puts “found it”
break
end
end

–Jeremy

On 12/6/07, Peter L. [email protected] wrote:

break

end
end

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

–
http://www.jeremymcanally.com/

My books:
Ruby in Practice

My free Ruby e-book

My blogs:

http://www.rubyinpractice.com/

3

Peter L. wrote:

Got help with this code earlier its just checking a file for a line

Im really new to ruby ive used java and C before

just wondering what do i put in if i want to use a variable that is
holding the string eg VAR1 = “hello”

File.foreach “file.txt” do |line|
if /hello/ =~ line
puts “found it”
break
end
end

var = “hello”
File.foreach “file.txt” do |line|
if /#{var}/ =~ line
puts “found it”
break
end
end

Perhaps?

Regards,
Lee

4

Peter L. wrote:

if /#{var1}/ =~ line

when i enter # thats just comments out the whole line
any reason for using #

is not a comment inside a regexp or string

Best regards,

Jari W.

5

if /#{var1}/ =~ line

when i enter # thats just comments out the whole line
any reason for using #

Jeremy McAnally wrote:

You can use string interpolation like you can with double quoted
strings.

var1 = “hello”

File.foreach “file.txt” do |line|
if /#{var1}/ =~ line
puts “found it”
break
end
end

6

Though your IDE may think you’re commenting out the whole line, you’re
not. It’s the proper way to do string interpolation.

See here: Ruby | zenspider.com | by ryan davis

Or, optionally, the Pickaxe book section on strings.

–Jeremy

On 12/6/07, Peter L. [email protected] wrote:

–
http://www.jeremymcanally.com/

My books:
Ruby in Practice

My free Ruby e-book

My blogs:

http://www.rubyinpractice.com/

7

Thanks for explaining it

Cheers
Loftz

Jeremy McAnally wrote:

Though your IDE may think you’re commenting out the whole line, you’re
not. It’s the proper way to do string interpolation.

See here: Ruby | zenspider.com | by ryan davis

Or, optionally, the Pickaxe book section on strings.

–Jeremy

On 12/6/07, Peter L. [email protected] wrote:

–
http://www.jeremymcanally.com/

My books:
Ruby in Practice
Ruby in Practice

My free Ruby e-book
http://www.humblelittlerubybook.com/

My blogs:
http://www.mrneighborly.com/
http://www.rubyinpractice.com/

8

Jano S. wrote:

(This might apply for 1.8 MRI only, other interpreters might be
different): When the regex literal contains #{}, the object
is created on each pass through the code. In the other case it’s
created only once.

True, you could use the Regexp class also then…

var = ‘hello’
revar = Regexp.new(var)

if revar =~ line
#…
end

or perhaps

var = ‘hello’
File.foreach ‘file.txt’ do |line|
if Regexp.new(var) =~ line
puts ‘found it’
break
end
end

If you don’t care how many times its created and you don’t want to use
the ‘#’ in your regexp matches because your IDE doesn’t know any better.

Regards,
Lee

9

On Dec 6, 2007 12:49 PM, Lee J. [email protected] wrote:

Sometimes it’s better to cache the /#{var}/ as in this case, new
regexp object is created on each pass through the cycle.
That might hurt the performance a bit. So:

var = “hello”

  • var_re = /#{var}/

File.foreach “file.txt” do |line|

  • if /#{var}/ =~ line
  • if var_re =~ line
puts "found it"
break

end
end

(This might apply for 1.8 MRI only, other interpreters might be
different): When the regex literal contains #{}, the object
is created on each pass through the code. In the other case it’s
created only once.

Jano

10

On Dec 6, 6:38 am, Jano S. [email protected] wrote:

  • if /#{var}/ =~ line
    created only once.

Jano

You can also use the /o option, which tells Ruby to compile the Regex
only once:

var = “hello”
File.foreach “file.txt” do |line|
if /#{var}/o =~ line
puts “found it”
break
end
end

11

On Dec 6, 2007 4:35 PM, yermej [email protected] wrote:

end

Thanks, I didn’t know that… Now I see it even in the first pickaxe
book… I guess I should read it once more :wink:

12

On Dec 6, 2007 5:17 AM, Lee J. [email protected] wrote:

True, you could use the Regexp class also then…

var = ‘hello’
revar = Regexp.new(var)

And don’t miss the very useful Regexp.quote, which makes sure

everything in var is matched literally

revar = Regexp.new(Regexp.quote(var))

martin