AKA How do I find an unescaped character sequence with regex?
Given an environment set up with:
#secret = "OH NO!"
$secret = "OH NO!"
##secret = "OH NO!"
and given string read in from a file that looks like this:
some_str = '"\"#{:NOT&&:very}\" bad. \u262E\n##secret \\#$secret \\\\###secret"'
I want to evaluate this as a Ruby string, but without interpolation. Thus, the result should be:
puts safe_eval(some_str)
#=> "#{:NOT&&:very}" bad. ☮
#=> ##secret #$secret \###secret
By contrast, the eval-only solution produces
puts eval(some_str)
#=> "very" bad. ☮
#=> OH NO! #$secret \OH NO!
At first I tried:
def safe_eval(str)
eval str.gsub(/#(?=[{#$])/,'\\#')
end
but this fails in the malicious middle case above, producing:
#=> "#{:NOT&&:very}" bad. ☮
#=> ##secret \OH NO! \###secret
You can do this via regex by ensuring that there are an even number of backslashes before the character you want to escape:
def safe_eval(str)
eval str.gsub( /([^\\](?:\\\\)*)#(?=[{#$])/, '\1\#' )
end
…which says:
Find a character that is not a backslash [^\\]
followed by two backslashes (?:\\\\)
repeated zero or more times *
followed by a literal # character
and ensure that after that you can see either a {, #, or $ character.
and replace that with
the non-backslash-maybe-followed-by-even-number-of-backslashes
and then a backslash and then a #
How about not using eval at all? As per this comment in chat, all that's necessary are escaping quotes, newlines, and unicode characters. Here's my solution:
ESCAPE_TABLE = {
/\\n/ => "\n",
/\\"/ => "\"",
}
def expand_escapes(str)
str = str.dup
ESCAPE_TABLE.each {|k, v| str.gsub!(k, v)}
#Deal with Unicode
str.gsub!(/\\u([0-9A-Z]{4})/) {|m| [m[2..5].hex].pack("U") }
str
end
When called on your string the result is (in your variable environment):
"\"\"\#{:NOT&&:very}\" bad. ☮\n\##secret \\\#$secret \\\\\###secret\""
Although I would have preferred not to have to treat unicode specially, it is the only way to do it without eval.
Related
I have a list of Unicode character codes that I would like to output with rumoji. Here's the code I'm using to iterate over my data.
require "rumoji"
# this works
puts Rumoji.decode("\u{1F600}")
# feed some data
data = [
"1F600",
"1F476",
"1F474"
]
data.each do |line|
# this doesn't work
puts Rumoji.decode("\u{#{line}}")
puts Rumoji.decode("\u{" + line + "}")
end
I'm not sure how I can use variable names inside the escaped string.
One can not use \u along with string interpolation, since \u takes precedence. What one might do, is to Array#pack an array of integers:
▶ data.map { |e| e.to_i(16) }.pack 'U*'
#⇒ "😀👶👴"
I am trying to call the first duplicate character in my string in Ruby.
I have defined an input string using gets.
How do I call the first duplicate character in the string?
This is my code so far.
string = "#{gets}"
print string
How do I call a character from this string?
Edit 1:
This is the code I have now where my output is coming out to me No duplicates 26 times. I think my if statement is wrongly written.
string "abcade"
puts string
for i in ('a'..'z')
if string =~ /(.)\1/
puts string.chars.group_by{|c| c}.find{|el| el[1].size >1}[0]
else
puts "no duplicates"
end
end
My second puts statement works but with the for and if loops, it returns no duplicates 26 times whatever the string is.
The following returns the index of the first duplicate character:
the_string =~ /(.)\1/
Example:
'1234556' =~ /(.)\1/
=> 4
To get the duplicate character itself, use $1:
$1
=> "5"
Example usage in an if statement:
if my_string =~ /(.)\1/
# found duplicate; potentially do something with $1
else
# there is no match
end
s.chars.map { |c| [c, s.count(c)] }.drop_while{|i| i[1] <= 1}.first[0]
With the refined form from Cary Swoveland :
s.each_char.find { |c| s.count(c) > 1 }
Below method might be useful to find the first word in a string
def firstRepeatedWord(string)
h_data = Hash.new(0)
string.split(" ").each{|x| h_data[x] +=1}
h_data.key(h_data.values.max)
end
I believe the question can be interpreted in either of two ways (neither involving the first pair of adjacent characters that are the same) and offer solutions to each.
Find the first character in the string that is preceded by the same character
I don't believe we can use a regex for this (but would love to be proved wrong). I would use the method suggested in a comment by #DaveNewton:
require 'set'
def first_repeat_char(str)
str.each_char.with_object(Set.new) { |c,s| return c unless s.add?(c) }
nil
end
first_repeat_char("abcdebf") #=> b
first_repeat_char("abcdcbe") #=> c
first_repeat_char("abcdefg") #=> nil
Find the first character in the string that appears more than once
r = /
(.) # match any character in capture group #1
.* # match any character zero of more times
? # do the preceding lazily
\K # forget everything matched so far
\1 # match the contents of capture group 1
/x
"abcdebf"[r] #=> b
"abccdeb"[r] #=> b
"abcdefg"[r] #=> nil
This regex is fine, but produces the warning, "regular expression has redundant nested repeat operator '*'". You can disregard the warning or suppress it by doing something clunky, like:
r = /([^#{0.chr}]).*?\K\1/
where ([^#{0.chr}]) means "match any character other than 0.chr in capture group 1".
Note that a positive lookbehind cannot be used here, as they cannot contain variable-length matches (i.e., .*).
You could probably make your string an array and use detect. This should return the first char where the count is > 1.
string.split("").detect {|x| string.count(x) > 1}
I'll use positive lookahead with String#[] method :
"abcccddde"[/(.)(?=\1)/] #=> c
As a variant:
str = "abcdeff"
p str.chars.group_by{|c| c}.find{|el| el[1].size > 1}[0]
prints "f"
Problem
In a source file, I have a large number of strings. Some with interpolation, some with special symbols and some with neither.
I am trying to work out if I can replace the simple strings' double quotes with single quotes whilst leaving double quotes for the interpolated and special symbol strings. I would then run this conversion on one or more source code files.
I imagine there is probably a nice regex for this, but I can't quite formulate it.
Example - Code
Imagine the following code:
def myfunc(var, var2 = "abc")
s = "something"
puts "a simple string"
puts "string with a single ' quote"
puts "string with a newline \n"
puts "my #{var}"
end
Example - Result
I would like to turn it into this:
def myfunc(var, var2 = 'abc')
s = 'something'
puts 'a simple string'
puts "string with a single ' quote"
puts "string with a newline \n"
puts "my #{var}"
end
If anyone has any ideas I'd be very grateful!
Assuming that you can read your string from your file by yourself into an array strings:
strings = [ "\"a simple string\"",
"\"string with a single ' quote\"",
"\"string with a newline \n\""
"\"my \#{var}\"" ]
then we would eval them to see how they behave:
$SAFE = 4
single_quoted_when_possible = strings.map { |double_quoted|
begin
string = eval( double_quoted ) # this string, as Ruby sees it
raise unless string.is_a? String
raise unless '"' + string + '"' == double_quoted
rescue
raise "Array element is not a string!"
end
begin
raise unless eval( "'#{string}'" ) == string
"'#{string}'"
rescue
double_quoted
end
}
And that SAFE level 4 is just woodoo, just an acknowledgement from me that we are doing something dangerous. I do not know to what extent it actually protects against all dangers.
In your particular case, you can create a Regexp heuristic, relying on hope that nobody will write "evil" strings in your code, such as /= *(".+") *$/ or /\w+ *\(* *(".+") *\)* *$/. That heuristic would extract some string suspects, to which you could further apply the method I wrote higher above. But I would still have human look at each replacement, and run tests on the resulting code afterwards.
I would like to keep \n when I print out strings in ruby,
Like now, if I use puts or print, \n will end up with a newline:
pry(main)> print "abc\nabc"
abc
abc
is there a way to let ruby print it out like: abc\nabc ?
UPDATE
Sorry that maybe I didn't make it more clear. I am debugging my regexps, so when I output a string, if a \n is displayed as a \n, not a newline, it would be easier for me to check. So #slivu 's answer is exactly what I want. Thanks guys.
i would suggest to use p instead of puts/print:
p "abc\nabc"
=> "abc\nabc"
and in fact with pry you do not need to use any of them, just type your string and enter:
str = "abc\nabc"
=> "abc\nabc"
str
=> "abc\nabc"
In Ruby, strings in a single quote literal, like 'abc\nabc' will not be interpolated.
1.9.3p194 :001 > print 'abc\nabc'
abc\nabc => nil
vs with double quotes
1.9.3p194 :002 > print "abc\nabc"
abc
abc => nil
Because \n is a special keyword, you have to escape it, by adding a backslash before the special keyword (and because of that, backslashes must also be escaped), like so: abs\\nabc. If you wanted to print \\n, you would have to replace it to be abs\\\\n, and so on (two backslashes to display a backslash).
You can also just use single quotes instead of double quotes so that special keywords will not be interpreted. This, IMHO, is bad practice, but if it makes your code look nicer, I guess it's worth it :)
Here are some examples of ways you can escape (sort of like a TL;DR version):
puts 'abc\nabc' # Single quotes ignore special keywords
puts "abc\\nabc" # Escaping a special keyword (preferred technique, IMHO)
p "abc\nabc" # The "p" command does not interpret special keywords
You can also do it like this
puts 'abc\nabc'
Use %q to create a string for example:
str = %q{abc\nklm}
puts str #=> 'abc\nklm'
or
puts %q{abc\nklm}
or use escape character
puts "abc\\nklm"
To print the string: abc\nabc
The coded string must be: abc\\nabc which will not generate a newline.
Does anyone know of a Ruby gem (or built-in, or native syntax, for that matter) that operates on the outer quote marks of strings?
I find myself writing methods like this over and over again:
remove_outer_quotes_if_quoted( myString, chars ) -> aString
add_outer_quotes_unless_quoted( myString, char ) -> aString
The first tests myString to see if its beginning and ending characters match any one character in chars. If so, it returns the string with quotes removed. Otherwise it returns it unchanged. chars defaults to a list of quote mark characters.
The second tests myString to see if it already begins and ends with char. If so, it returns the string unchanged. If not, it returns the string with char tacked on before and after, and any embedded occurrance of char is escaped with backslash. char defaults to the first in a default list of characters.
(My hand-cobbled methods don't have such verbose names, of course.)
I've looked around for similar methods in the public repos but can't find anything like this. Am I the only one that needs to do this alot? If not, how does everyone else do this?
If you do it a lot, you may want to add a method to String:
class String
def strip_quotes
gsub(/\A['"]+|['"]+\Z/, "")
end
end
Then you can just call string.strip_quotes.
Adding quotes is similar:
class String
def add_quotes
%Q/"#{strip_quotes}"/
end
end
This is called as string.add_quotes and uses strip_quotes before adding double quotes.
This might 'splain how to remove and add them:
str1 = %["We're not in Kansas anymore."]
str2 = %['He said, "Time flies like an arrow, Fruit flies like a banana."']
puts str1
puts str2
puts
puts str1.sub(/\A['"]/, '').sub(/['"]\z/, '')
puts str2.sub(/\A['"]/, '').sub(/['"]\z/, '')
puts
str3 = "foo"
str4 = 'bar'
[str1, str2, str3, str4].each do |str|
puts (str[/\A['"]/] && str[/['"]\z/]) ? str : %Q{"#{str}"}
end
The original two lines:
# >> "We're not in Kansas anymore."
# >> 'He said, "Time flies like an arrow, Fruit flies like a banana."'
Stripping quotes:
# >> We're not in Kansas anymore.
# >> He said, "Time flies like an arrow, Fruit flies like a banana."
Adding quotes when needed:
# >> "We're not in Kansas anymore."
# >> 'He said, "Time flies like an arrow, Fruit flies like a banana."'
# >> "foo"
# >> "bar"
I would use the value = value[1...-1] if value[0] == value[-1] && %w[' "].include?(value[0]). In short, this simple code checks whether first and last char of string are the same and removes them if they are single/double quote. Additionally as many as needed quote types can be added.
%w["adadasd" 'asdasdasd' 'asdasdasd"].each do |value|
puts 'Original value: ' + value
value = value[1...-1] if value[0] == value[-1] && %w[' "].include?(value[0])
puts 'Processed value: ' + value
end
The example above will print the following:
Original value: "adadasd"
Processed value: adadasd
Original value: 'asdasdasd'
Processed value: asdasdasd
Original value: 'asdasdasd"
Processed value: 'asdasdasd"