# Unless =~ vs. ! =~

**URL:** <https://www.ruby-forum.com/t/unless-vs/66446>\
**Category:** Ruby\
**Created:** [August 25, 2006, 4:31pm UTC](https://www.ruby-forum.com/t/unless-vs/66446 "2006-08-25T16:31:17Z")\
**Posts on this page:** 6\
**Page:** 1

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**Author:** ![mclow](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/d6d6ee/32.png) [@mclow](https://www.ruby-forum.com/u/mclow)\
**Post date:** [August 25, 2006, 4:31pm UTC](https://www.ruby-forum.com/t/unless-vs/66446/1 "2006-08-25T16:31:17Z")

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Hi!

Could someone please help me understanding why the next two lines of  
code are different?

next unless line =~ /=/

next if !line =~ /=/

Thanks,  
Marco

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<div class="post-metadata">

**Author:** ![mclow](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/d6d6ee/32.png) [@mclow](https://www.ruby-forum.com/u/mclow)\
**Post date:** [August 25, 2006, 4:37pm UTC](https://www.ruby-forum.com/t/unless-vs/66446/2 "2006-08-25T16:37:25Z")

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Marco L. wrote:

> Could someone please help me understanding why the next two lines of  
> code are different?
> 
> next unless line =~ /=/
> 
> next if !line =~ /=/

I found out: it’s a operators precedence problem.

next unless line =~ /=/  
next if !(line =~ /=/) # with parenthesis

Marco

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<div class="post-metadata">

**Author:** ![mclow](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/d6d6ee/32.png) [@mclow](https://www.ruby-forum.com/u/mclow)\
**Post date:** [August 25, 2006, 4:37pm UTC](https://www.ruby-forum.com/t/unless-vs/66446/3 "2006-08-25T16:37:53Z")

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Marco L. wrote:

> Hi!
> 
> Could someone please help me understanding why the next two lines of  
> code are different?
> 
> next unless line =~ /=/
> 
> next if !line =~ /=/
> 
> Thanks,  
> Marco

I suspect !line =~ /=/ is not the same as !(line =~ /=/). Do you have  
more of an example that people can run in IRB to verify?

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<div class="post-metadata">

**Author:** ![mclow](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/d6d6ee/32.png) [@mclow](https://www.ruby-forum.com/u/mclow)\
**Post date:** [August 25, 2006, 4:51pm UTC](https://www.ruby-forum.com/t/unless-vs/66446/4 "2006-08-25T16:51:10Z")

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On Fri, 25 Aug 2006, Marco L. wrote:

> Thanks,  
> Marco

harp:~ \> cat a.rb  
require ‘yaml’

y “!‘foobar’” =\> (!‘foobar’)  
y “!‘foobar’ =~ /barfoo/” =\> (!‘foobar’ =~ /barfoo/)  
y “false =~ /barfoo/” =\> (false =~ /barfoo/)  
y “‘foobar’ !~ /barfoo/” =\> (‘foobar’ !~ /barfoo/)

harp:~ \> ruby a.rb  
a.rb:3: warning: string literal in condition  
a.rb:4: warning: string literal in condition

“!‘foobar’”: false  
“!‘foobar’ =~ /barfoo/”: false  
false =~ /barfoo/: false  
“‘foobar’ !~ /barfoo/”: true

! binds more tightly that =~

-a

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<div class="post-metadata">

**Author:** ![mclow](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/d6d6ee/32.png) [@mclow](https://www.ruby-forum.com/u/mclow)\
**Post date:** [August 25, 2006, 5:27pm UTC](https://www.ruby-forum.com/t/unless-vs/66446/5 "2006-08-25T17:27:15Z")

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On 25.08.2006 16:37, Marco L. wrote:

> next unless line =~ /=/  
> next if !(line =~ /=/) # with parenthesis

Note that you can also negate the match operator:

next if line !~ /=/

… or you use “not”

next if not line =~ /=/

My personal favorite here is your first one

next unless line =~ /=/

because it reads nice and clear.

Kind regards

```
robert
```

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<div class="post-metadata">

**Author:** ![mclow](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/d6d6ee/32.png) [@mclow](https://www.ruby-forum.com/u/mclow)\
**Post date:** [August 25, 2006, 5:27pm UTC](https://www.ruby-forum.com/t/unless-vs/66446/6 "2006-08-25T17:27:15Z")

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On Fri, Aug 25, 2006 at 11:37:25PM +0900, Marco L. wrote:

> next unless line =~ /=/  
> next if !(line =~ /=/) # with parenthesis

Have you considered this alternative?  
next if line !~ /=/

/me stirs the pot a little.