ruby code for modifying outer quotes on strings? - ruby

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"

Related

index out of string, ruby

Here's a small part of my code, pretty self explanatory, it copies all characters to temp from input and skips spaces.
input = gets.to_s.chomp
temp=String.new
for i in 0..input.length-1
if (input[i]==" ")
next
else
temp[i]=input[i]
end
end
puts "#{temp},END"
gets
However, i tested it with a 'hello world' input, and it should've given me helloworld But i'm getting
8:in '[]=':index 6 out of string(IndexError)
meaning the problem starts while it's skipping the space, for some reason.
keep in mind that i don't get any errors if i put a string that doesn't contain a space
Whenever string manipulation is required, it may be desirable to convert the string to an array of its parts, manipulate those parts and then join them back into a string, but more often as not it is simpler to just operate on the string itself, mainly using methods from the class String. Here you could Kernel#puts the following.
"%s END" % gets.delete(" \n")
#=> "helloworld"
String#delete removes both spaces and the return character ("\n") that Kernel#gets tacks onto the end of the string that is entered. A variant of this is "%s END" % gets.chomp.delete(" ").
Another way would be to puts
"%s END" % gets.gsub(/\s/, '')
#=> "helloworld"
The regular expression /\s/, causes String#gsub to remove all whitespace, which includes both spaces (and tabs) that are entered and the "\n" that gets tacks on to the end of the string.
I guess your error is due to the difference between the string 'hello world' and that you're "rejecting" whitespaces. In such case, for each whitespace in the string being used, the temp will have one less.
You can assign the input[i] when isn't a whitespace to the temp variable in the position temp.size, this way you don't skip indexes.
It could be temp[temp.size] or just modifying temp with +=.
for i in 0...input.size
if input[i] == ' '
next
else
temp[temp.size] = input[i]
end
end
Note you can replace the for loop for each (the Ruby way):
input = 'hello world'
temp = ''
(0...input.size).each do |index|
input[index] == ' ' ? next : temp[temp.size] = input[index]
end
# helloworld
If you want to skip all white spaces from your input and print the output, you can do so with a one-liner:
puts "#{gets.chomp.split.join}, END"
In ruby, you hardly need to write loops using for construct unlike other traditional languages like Java.

How to replace a specific character in a string along with the immediate next character

I have a string of text:
string = "%hello %world ho%w is i%t goin%g"
I want to return the following:
"Hello World hoW is iT goinG
The % sign is a key that tells me the next character should be capitalized. The closest I have gotten so far is:
#thing = "%this is a %test this is %only a %test"
if #thing.include?('%')
indicator_position = #thing.index("%")
lowercase_letter_position = indicator_position + 1
lowercase_letter = #thing[lowercase_letter_position]
#thing.gsub!("%#{lowercase_letter}","#{lowercase_letter.upcase}")
end
This returns:
"This is a Test this is %only a Test"
It looks like I need to iterate through the string to make it work as it is only replacing the lowercase 't' but I can't get it to work.
You can do this with gsub and a block:
string.gsub(/%(.)/) do |m|
m[1].upcase
end
Using a block allows you to run arbitrary code on each match.
Inferior to #tadman, but you could write:
string.gsub(/%./, &:upcase).delete('%')
#=> "Hello World hoW is iT goinG

Eval a string without string interpolation

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.

Ruby HERE-DOC method parameter passing

I am trying to use a custom method with here-doc and want to pass parameter (there is no business case, I am merely trying to learn ruby). Is there a way to pass parameter in this case? This is what I have so far.
Simple method, just works fine.
def meth1
self.upcase
end
str1 = <<MY.meth1
i am a small case string
MY
# "I AM A SMALL CASE STRING\n"
Now, I thought let us drop some parameters and tried different variations and irb gives me a blank stare.
#variation 1
def meth2( <<EOF1, <<EOF2 )
EOF1.upcase + "..." + EOF2.downcase
end
str2 = <<MY.meth2
some string
EOF1
ANOTHER STRING
EOF2
MY
My guess is that this is what you are trying to do:
def meth2(str1, str2)
str1.upcase + "..." + str2.downcase
end
str2 = meth2(<<EOF1, <<EOF2)
some string
EOF1
ANOTHER STRING
EOF2
str2 # => " SOME STRING\n... another string\n"
If you don't intent to indent, see here. ← See my play with words here?
try something along the lines of
something = "bananas"
str = <<EOF
this has some #{something} in!
EOF
Try something like this:
def meth2( item1, item2 )
item1.upcase + "..." + item2.downcase
end
str2 = meth2 <<EOF1, <<EOF2
some string
EOF1
ANOTHER STRING
EOF2
The problem you are having is due to not fully understanding how heredoc-style string literals work. The <<DELIMITER part just is telling the parser to get it's string data from the lines that follow it. If there is more than one <<DELIMITER on a line, then they stack, and are read in in sequence. So, in this case, the code above is exactly equivalent to:
def meth2( item1, item2 )
item1.upcase + "..." + item2.downcase
end
str2 = meth2 " some string\n", " ANOTHER STRING\n"
Most importantly, there is no way to build a heredoc into a function like you were trying to do there... They can only be used in the same places and manner that other String literals, such as "double quoted" or 'single quoted' literals, can be used.

Smart conversion of double to single quotes in ruby

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.

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