What is the Ruby String sub function?

Question

I'm trying to convert a Ruby script into a Python script (having absolutely no understanding of the various functions in Ruby) and can't find anything on the Ruby sub function.

Here's the function I'm trying to translate:

def getCCache(arg1, arg2, arg3)
    local4 = Digest::MD5.hexdigest(arg1 + arg2)
    local5 = 0
    while (local5 < arg3.length)
        temp1 = arg3[local5]
        temp2 = local5
        local5 += local5;
        local4.sub(temp1, arg3[temp2])
        local5 += 1
    end
    return (local4)
end

The line I'm having trouble with is local4.sub(temp1, arg3[temp2]). What does the sub function do? If there's an equivalent in Python I would appreciate that as well.

ruby-doc.org/core-2.1.0/String.html#method-i-sub - I'd have to say that's some horribly obscure Ruby you are converting. Variables called arg, temp and local - in fact it looks like it has been deliberately obfuscated? — Neil Slater
– Neil Slater, Commented Dec 29, 2013 at 21:12
I think it's less deliberately obfuscated and more poorly coded by the original programmer. — avorum
– avorum, Commented Dec 29, 2013 at 21:18
Is some sort of code generator involved in this or did a human actually write that code? Near as I can tell, that whole mess is just a long and confusing way to say Digest::MD5.hexdigest(arg1 + arg2). — mu is too short
– mu is too short, Commented Dec 29, 2013 at 21:38
I doubt you did a search for "ruby sub", which is the most obvious first step. — the Tin Man
– the Tin Man, Commented Dec 29, 2013 at 22:51
I did, all it brought up for me was references for the gsub method — avorum
– avorum, Commented Dec 30, 2013 at 6:23

steenslag · Accepted Answer · 2013-12-29 22:54:05Z

2

local4.sub(temp1, arg3[temp2])

does nothing. It returns a copy of the string local4 with the first occurance of the substring referenced by temp1 substituted by the second argument. Then the result is discarded : no variable is assigned to the result.

local4 = local4.sub(temp1, arg3[temp2]) #or
local4.sub!(temp1, arg3[temp2])

would both do string substitution.

edited Dec 29, 2013 at 22:54

answered Dec 29, 2013 at 21:28

steenslag

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1 Comment

avorum Over a year ago

Interesting. Now I'm really wondering what the hell's going on here. Thanks for answering my question.

user2107733 · Accepted Answer · 2013-12-29 21:43:32Z

0

sub(pattern) {|...| block } → $_
Equivalent to $_.sub(args), except that $_ will be updated if substitution occurs. Available only when -p/-n command line option specified.

$_ is a ruby global variable and it represents string last read by gets

answered Dec 29, 2013 at 21:43

user2107733

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