Why this works fine:
t="
"+$<.read;puts t.reverse==t ?"YES":"NO"
but this:
t="
"+$<.read;puts t==t.reverse ?"YES":"NO"
says:
A.rb:2: syntax error, unexpected tCHAR, expecting $end
"+$<.read;puts t==t.reverse ?"YES":"NO"
^
I use ruby 1.9.2p290 (2011-07-09) [i386-mingw32].
Sample STDIN string is XX.\n...\n.XX\n.
Looks like Ruby is parsing the latter as a potential call to #reverse?. That ambiguity is removed when switched the other way. Adding parentheses around the conditional should allow it to go both ways.
Related
I'm getting different error based on space between after divide(/) operator. Lets consider following example.
$ ruby -e "a /100"
-e:1: unterminated string meets end of file
-e:1: syntax error, unexpected tSTRING_END, expecting tSTRING_CONTENT or tREGEXP_END or tSTRING_DBEG or tSTRING_DVAR
$ ruby -e "a / 100"
-e:1: undefined local variable or method `a' for main:Object (NameError)
The second example gives proper error message while the first one gives weird error. I did some research, but couldn't find out the reasons behind it. Is there anyway to fix this to give proper error messge?
If I try this with Ruby 2.3.1, I get this message: -e:1: unterminated regexp meets end of file Which seems valid since "/" is normally a regex marker...
And in the second line of your error message it says it is expecting a tREGEXP_END.
So, I think, everything is fine.
I tried this in the terminal and got the same regexp error:
$ ruby -e "a /100"
-e:1: unterminated regexp meets end of file
It seems like the /100 was interpreted as a regexp. The simple solution is to follow the correct ruby syntax (i.e. your second example: $ ruby -e "a / 100" ). Normally, it is recommended to add spaces around ruby operators, as suggest by the ruby style guide.
A simple Ruby program, which works well (using Ruby 2.0.0):
#!/usr/bin/ruby
while gets
print if /foo/../bar/
end
However, Ruby also outputs the warning warning: regex literal in condition. It seems that Ruby considers my flip-flop-expression /foo/../bar/ as dangerous.
My question: Where lies the danger in this program? And: Can I turn off this warning (ideally only for this statement, keeping other warnings active)?
BTW, I found on the net several discussions of this kind of code, also mentioning the warning, but never found a good explanation why we get warned.
You can avoid the warning by using an explicit match:
while gets
print if ~/foo/..~/bar/
end
Regexp#~ matches against $_.
I don't know why the warning is shown (to be honest, I wasn't even aware that Ruby matches regexp literals against $_ implicitly), but according to the parser's source code, it is shown unless you provide the -e option when invoking Ruby, i.e. passing the script as an argument:
$ ruby -e "while gets; print if /foo/../bar/ end"
I would avoid using $_ as an implicit parameter and instead use something like:
while line = gets
print line if line=~/foo/..line=~/bar/
end
I think Neil Slater is right: It looks like a bug in a parser. If I change the code to
#!/usr/bin/ruby
while gets
print if $_=~/foo/..$_=~/bar/
end
the warning disappears.
I'll file a bug report.
When you come across numbers that look like this in Ruby code, what does it mean?
1r
Or
1.0r
Tested in Ruby 1.8.6 up to 2.0.0 and it fails. with something like this:
>> 1r
SyntaxError: unexpected tIDENTIFIER, expecting end-of-input
and
>> 1.0r
SyntaxError: unexpected tIDENTIFIER, expecting end-of-input
Probably downvoted for not searching, or something, or not enough examples. Hopefully this clarifies. It is just Ruby Code, it doesn't have to be specifically anywhere, just has to be there.
That is a new feature for Decimal/Rational Literals in Ruby 2.1. See here: http://rkh.im/ruby-2.1 (search for "Decimal Literals")
0.1r #=> (1/10)
0.1r * 3 #=> (3/10)
syntax error, unexpected $end, expecting keyword_end
We’ve all been there! Assuming enough code changed that a quick glance at git diff or the like doesn’t make it obvious, is there an easy way to find that missing end (short of switching to an indentation-based language like Python)?
FWIW, I use Sublime Text 2 as my editor.
If you're using Ruby 1.9, try the -w flag when running your ruby program.
# t.rb
class Example
def meth1
if Time.now.hours > 12
puts "Afternoon"
end
def meth2
# ...
end
end
ruby t.rb
=> t.rb:10: syntax error, unexpected $end, expecting keyword_end
ruby -w t.rb
=> t.rb:5: warning: mismatched indentations at 'end' with 'if' at 3
t.rb:9: warning: mismatched indentations at 'end' with 'def' at 2
t.rb:10: syntax error, unexpected $end, expecting keyword_end
Source:
http://pragdave.blogs.pragprog.com/pragdave/2008/12/ruby-19-can-check-your-indentation.html
Edit (2023): this is now part of Ruby 3.2 and doesn‘t need to be required separately!
————————————
Edit (2022): the gem is now called syntax_suggest and is part of the Ruby standard library!
————————————
Since December 2020, there is also the dead_end gem which helps you detect missing ends.
The easiest way to get started is to install the gem:
gem install dead_end
and run it directly from your console, providing the file name to scan:
dead_end myfile.rb
This will provide you with a more helpful error message:
43 if (col_idx - 1) % 3 == 0
50 if !contains?(doc, node)
❯ 51 doc.add_child(node)
❯ 52 tree.
53 end
54 end
See the documentation for more options.
If you're using rails, you can run the problematic file specifically with the -w flag.
If you still can't find the offending mismatch, then my go-to way of solving this problem is just commenting out chunks of code until I can isolate the problematic area.
On OS X you can use command + / to comment out the highlighted piece of text.
I just installed Ruby 1.9.2 after having used 1.8.7, as there is a feature I need. I had called many of my methods like this:
do_something (arg0, arg1)
With 1.9.2, i get the following error, syntax error, unexpected ',', expecting ')' and the fix seems to be:
do_something arg0, arg1
But this could take me hours to fix all the cases. Is there a way around this? Why is it an error in the first place? thanks
The extra space is the culprit. Use:
do_something(arg0, arg1)