I am trying to use gsub or sub on a regex passed through terminal to ARGV[].
Query in terminal: $ruby script.rb input.json "\[\{\"src\"\:\"
Input file first 2 lines:
[{
"src":"http://something.com",
"label":"FOO.jpg","name":"FOO",
"srcName":"FOO.jpg"
}]
[{
"src":"http://something123.com",
"label":"FOO123.jpg",
"name":"FOO123",
"srcName":"FOO123.jpg"
}]
script.rb:
dir = File.dirname(ARGV[0])
output = File.new(dir + "/output_" + Time.now.strftime("%H_%M_%S") + ".json", "w")
open(ARGV[0]).each do |x|
x = x.sub(ARGV[1]),'')
output.puts(x) if !x.nil?
end
output.close
This is very basic stuff really, but I am not quite sure on how to do this. I tried:
Regexp.escape with this pattern: [{"src":".
Escaping the characters and not escaping.
Wrapping the pattern between quotes and not wrapping.
Meditate on this:
I wrote a little script containing:
puts ARGV[0].class
puts ARGV[1].class
and saved it to disk, then ran it using:
ruby ~/Desktop/tests/test.rb foo /abc/
which returned:
String
String
The documentation says:
The pattern is typically a Regexp; if given as a String, any regular expression metacharacters it contains will be interpreted literally, e.g. '\d' will match a backlash followed by ‘d’, instead of a digit.
That means that the regular expression, though it appears to be a regex, it isn't, it's a string because ARGV only can return strings because the command-line can only contain strings.
When we pass a string into sub, Ruby recognizes it's not a regular expression, so it treats it as a literal string. Here's the difference in action:
'foo'.sub('/o/', '') # => "foo"
'foo'.sub(/o/, '') # => "fo"
The first can't find "/o/" in "foo" so nothing changes. It can find /o/ though and returns the result after replacing the two "o".
Another way of looking at it is:
'foo'.match('/o/') # => nil
'foo'.match(/o/) # => #<MatchData "o">
where match finds nothing for the string but can find a hit for /o/.
And all that leads to what's happening in your code. Because sub is being passed a string, it's trying to do a literal match for the regex, and won't be able to find it. You need to change the code to:
sub(Regexp.new(ARGV[1]), '')
but that's not all that has to change. Regexp.new(...) will convert what's passed in into a regular expression, but if you're passing in '/o/' the resulting regular expression will be:
Regexp.new('/o/') # => /\/o\//
which is probably not what you want:
'foo'.match(/\/o\//) # => nil
Instead you want:
Regexp.new('o') # => /o/
'foo'.match(/o/) # => #<MatchData "o">
So, besides changing your code, you'll need to make sure that what you pass in is a valid expression, minus any leading and trailing /.
Based on this answer in the thread Convert a string to regular expression ruby, you should use
x = x.sub(/#{ARGV[1]}/,'')
I tested it with this file (test.rb):
puts "You should not see any number [0123456789].".gsub(/#{ARGV[0]}/,'')
I called the file like so:
ruby test.rb "\d+"
# => You should not see any number [].
Related
I'm writing a simple method to detect and strip tags from text strings. Given this input string:
{{foobar}}
The function has to return
foobar
I thought I could just chain multiple chomp! methods, like so:
"{{foobar}}".chomp!("{{").chomp!("}}")
but this won't work, because the first chomp! returns a NilClass. I can do it with regular chomp statements, but I'm really looking for a one-line solution.
The String class documentation says that chomp! returns a Str if modifications have been made - therefore, the second chomp! should work. It doesn't, however. I'm at a loss at what's happening here.
For the purposes of this question, you can assume that the input string is always a tag which begins and ends with double curly braces.
You can definitely chain multiple chomp statements (the non-bang version), still having a one-line solution as you wanted:
"{{foobar}}".chomp("{{").chomp("}}")
However, it will not work as expected because both chomp! and chomp removes the separator only from the end of the string, not from the beginning.
You can use sub
"{{foobar}}".sub(/{{(.+)}}/, '\1')
# => "foobar"
"alfa {{foobar}} beta".sub(/{{(.+)}}/, '\1')
# => "alfa foobar beta"
# more restrictive
"{{foobar}}".sub(/^{{(.+)}}$/, '\1')
# => "foobar"
Testing this out, it's clear that chomp! will return nil if the separator it's provided as an argument is not present at the end of the string.
So "{{text}}".chomp!("}}") returns a string, but "{{text}}".chomp!("{{") reurns nil.
See here for an answer of how to chomp at the beginning of a string. But recognize that chomp only looks at the end of the string. So you can call str.reverse.chomp!("{{").reverse to remove the opening brackets.
You could also use a regex:
string = "{{text}}"
puts [/^\{\{(.+)\}\}$/, 1]
# => "text"
Try tr:
'{{foobar}}'.tr('{{', '').tr('}}', '')
You can also use gsub or sub but if the replacement is not needed as pattern, then tr should be faster.
If there are always curly braces, then you can just slice the string:
'{{foobar}}'[2...-2]
If you plan to make a method which returns the string without curly braces then DO NOT use bang versions. Modifying the input parameter of a method will be suprising!
def strip(string)
string.tr!('{{', '').tr!('}}', '')
end
a = '{{foobar}}'
b = strip(a)
puts b #=> foobar
puts a #=> foobar
I see in the documentation I'm able to do:
/\$(?<dollars>\d+)\.(?<cents>\d+)/ =~ "$3.67" #=> 0
puts dollars #=> prints 3
I was wondering if this would be possible:
string = "\$(\?<dlr>\d+)\.(\?<cts>\d+)"
/#{Regexp.escape(string)}/ =~ "$3.67"
I get:
`<main>': undefined local variable or method `dlr' for main:Object (NameError)
There are a few mistakes in your approach. First of all, let's look at your string:
string = "\$(\?<dlr>\d+)\.(\?<cts>\d+)"
You escape the dollar sign with "\$", but that is the same as just writing "$", consider:
"\$" == "$"
#=> true
To actually end up with the string "backslash followed by dollar" you would need to write "\\$". The same thing applies to the decimal character classes, you would have to write "\\d" to end up with the correct string.
The question marks on the other hand are actually part of the regex syntax, so you do not want to escape these at all. I recommend using single quotes for your original string, because that makes the input much easier:
string = '\$(?<dlr>\d+)\.(?<cts>\d+)'
#=> "\\$(?<dlr>\\d+)\\.(?<cts>\\d+)"
The next issue is with Regexp.escape. Take a look at what regular expression it produces with the above string:
string = '\$(?<dlr>\d+)\.(?<cts>\d+)'
Regexp.escape(string)
#=> "\\\\\\$\\(\\?<dlr>\\\\d\\+\\)\\\\\\.\\(\\?<cts>\\\\d\\+\\)"
That's one level too much escaping. Regexp.escape can be used when you want to match the literal characters that are contained in the string. For example, the escaped regex above will match the source string itself:
/#{Regexp.escape(string)}/ =~ string
#=> 0 # matches at offset 0
Instead, you can use Regexp.new to treat the source as an actual regular expression.
The last issue is then how you access the match result. Obviously, you are getting a NoMethodError. You might think that the match result is stored in local variables called dlr and cts, but that is not the case. You have two options to access the match data:
Use Regexp.match, it will return a MatchData object as result
Use regexp =~ string and then access the last match data with the global variable $~
I prefer the former, because it is easier to read. The full code would then look like this:
string = '\$(?<dlr>\d+)\.(?<cts>\d+)'
regexp = Regexp.new(string)
result = regexp.match("$3.67")
#=> #<MatchData "$3.67" dlr:"3" cts:"67">
result[:dlr]
#=> "3"
result[:cts]
#=> "67"
I am trying to escape certain characters in a string. In particular, I want to turn
abc/def.ghi into abc\/def\.ghi
I tried to use the following syntax:
1.9.3p125 :076 > "abc/def.ghi".gsub(/([\/.])/, '\\\1')
=> "abc\\1def\\1ghi"
Hmm. This behaves as if capture replacements didn't work. Yet, when I tried this:
1.9.3p125 :075 > "abc/def.ghi".gsub(/([\/.])/, '\1')
=> "abc/def.ghi"
... I got the replacement to work, but, of course, my prefixes weren't part of it.
What is the correct syntax to do something like this?
This should be easier
gsub(/(?=[.\/])/, "\\")
If you are trying to prepare a string to be used as a regex pattern, use the right tool:
Regexp.escape('abc/def.ghi')
=> "abc/def\\.ghi"
You can then use the resulting string to create a regex:
/#{ Regexp.escape('abc/def.ghi') }/
=> /abc\/def\.ghi/
or:
Regexp.new(Regexp.escape('abc/def.ghi'))
=> /abc\/def\.ghi/
From the docs:
Escapes any characters that would have special meaning in a regular expression. Returns a new escaped string, or self if no characters are escaped. For any string, Regexp.new(Regexp.escape(str))=~str will be true.
Regexp.escape('\*?{}.') #=> \\\*\?\{\}\.
You can pass a block to gsub:
>> "abc/def.ghi".gsub(/([\/.])/) {|m| "\\#{m}"}
=> "abc\\/def\\.ghi"
Not nearly as elegant as #sawa's answer, but it was the only way I could find to get it to work if you need the replacing string to contain the captured group/backreference (rather than inserting the replacement before the look-ahead).
Is there a way to check in Ruby whether the string "1:/2" is contained within a larger string str, beside iterating over all positions of str?
You can use the include? method
str = "wdadwada1:/2wwedaw"
# => "wdadwada1:/2wwedaw"
str.include? "1:/2"
# => true
A regular expression will do that.
s =~ /1:\/2/
This will return either nil if s does not contain the string, or the integer position if it does. Since nil is falsy and an integer is truthy, you can use this expression in an if statement:
if s =~ /1:\/2/
...
end
The regular expression is normally delimited by /, which is why the slash within the regular expression is escaped as \/
It is possible to use a different delimiter to avoid having to escape the /:
s =~ %r"1:/2"
You could use other characters than " with this syntax, if you want.
The simplest and most straight-forward is to simply ask the string if it contains the sub-string:
"...the string 1:/2 is contained..."['1:/2']
# => "1:/2"
!!"...the string 1:/2 is contained..."['1:/2']
# => true
The documentation has the full scoop; Look at the last two examples.
I have a very large string that needs to escape all the single quotes in it, so I can feed it to JavaScript without upsetting it.
I have no control over the external string, so I can't change the source data.
Example:
Cote d'Ivoir -> Cote d\'Ivoir
(the actual string is very long and contains many single quotes)
I'm trying to this by using gsub on the string, but can't get this to work:
a = "Cote d'Ivoir"
a.gsub("'", "\\\'")
but this gives me:
=> "Cote dIvoirIvoir"
I also tried:
a.gsub("'", 92.chr + 39.chr)
but got the same result; I know it's something to do with regular expressions, but I never get those.
The %q delimiters come in handy here:
# %q(a string) is equivalent to a single-quoted string
puts "Cote d'Ivoir".gsub("'", %q(\\\')) #=> Cote d\'Ivoir
The problem is that \' in a gsub replacement means "part of the string after the match".
You're probably best to use either the block syntax:
a = "Cote d'Ivoir"
a.gsub(/'/) {|s| "\\'"}
# => "Cote d\\'Ivoir"
or the Hash syntax:
a.gsub(/'/, {"'" => "\\'"})
There's also the hacky workaround:
a.gsub(/'/, '\#').gsub(/#/, "'")
# prepare a text file containing [ abcd\'efg ]
require "pathname"
backslashed_text = Pathname("/path/to/the/text/file.txt").readlines.first.strip
# puts backslashed_text => abcd\'efg
unslashed_text = "abcd'efg"
unslashed_text.gsub("'", Regexp.escape(%q|\'|)) == backslashed_text # true
# puts unslashed_text.gsub("'", Regexp.escape(%q|\'|)) => abcd\'efg