RegEx For Multiple Search & Replace

Question

I'm trying to do a search and replace (for multiple chars) in the following string:

VAR=%2FlkdMu9zkpE8w7UKDOtkkHhJlYZ6CaEaxqmsA%2B7G3e8%3D&

One or more of these characters: %3D, %2F, %2B, %23, can be found anywhere (beginning, middle, or end of the string) and ideally, I'd like to search for all of them at once (using one regex) and replace them with = or / or + or # respectively, then return the final string.

Example 1:

VAR=%2FlkdMu9zkpE8w7UKDOtkkHhJlYZ6CaEaxqmsA%2B7G3e8%3D&

Should return

VAR=/lkdMu9zkpE8w7UKDOtkkHhJlYZ6CaEaxqmsA+7G3e8=&

Example 2:

VAR=s2P0n6I%2Flonpj6uCKvYn8PCjp%2F4PUE2TPsltCdmA%3DRQPY%3D&

Should return

VAR=s2P0n6I/lonpj6uCKvYn8PCjp/4PUE2TPsltCdmA=RQPY=&

What language are you doing this in? Your language probably has a native way to urldecode. — Joseph Silber
– Joseph Silber, Commented Sep 15, 2013 at 20:18
A single regex? You'll need a function to pick which set of chars to replace with the corresponding set of chars as well. — Jerry
– Jerry, Commented Sep 15, 2013 at 20:21
Python, BUT what I'm looking for is a simple expression, not lines of code or scripts. Something like this:'VAR':\s*'([^']*)' something that will step through the string, find and replace those characters. I found this, but I don't know how to apply it to my case: stackoverflow.com/questions/14059129/… — My PM
– My PM, Commented Sep 15, 2013 at 20:24
That question is different. The variables replaced are already in the string, while yours aren't. — Jerry
– Jerry, Commented Sep 15, 2013 at 20:29

Wolph · Accepted Answer · 2013-09-15 20:45:27Z

2

I'm not convinced you need regex for this, but it's fairly easy to do with Python:

x = 'VAR=%2FlkdMu9zkpE8w7UKDOtkkHhJlYZ6CaEaxqmsA%2B7G3e8%3D&'

import re

MAPPING = { 
    '%3D': '=',
    '%2F': '/',
    '%2B': '+',
    '%23': '#',
}

def replace(match):
    return MAPPING[match.group(0)]

print x
print re.sub('%[A-Z0-9]{2}', replace, x)

Output:

VAR=%2FlkdMu9zkpE8w7UKDOtkkHhJlYZ6CaEaxqmsA%2B7G3e8%3D&
VAR=/lkdMu9zkpE8w7UKDOtkkHhJlYZ6CaEaxqmsA+7G3e8=&

answered Sep 15, 2013 at 20:45

Wolph

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3 Comments

My PM Over a year ago

That's great and I could follow what you did, but is there a way to do this using some slick regex or is it just not possible? Cheers Mate!

Ofir Israel Over a year ago

Look at my answer, is that what you call "slick"?

Wolph Over a year ago

@MyPM: since there is no simple metohd to convert the hex numbers into characters with the Python regex engine, no. You will always need to use a function like Ofir and I did or use multiple replaces like CodeChords did.

Israel Unterman · Accepted Answer · 2013-09-15 20:49:13Z

2

There is no need for a regex to do that in your example. A simple replace method will do:

def rep(s):
    for pat, txt in [['%2F','/'], ['%2B','+'], ['%3D','='], ['%23','#']]:
        s = s.replace(pat, txt)
    return s

answered Sep 15, 2013 at 20:49

Israel Unterman

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Comments

Ofir Israel · Accepted Answer · 2013-09-15 20:51:19Z

2

I'm also not convinced you need regex, but there's a better way to do url-decode with regex. Basically you need that every string in the pattern of %XX will be converted into the char it represents. This can be done with re.sub() like so:

>>> VAR="%2FlkdMu9zkpE8w7UKDOtkkHhJlYZ6CaEaxqmsA%2B7G3e8%3D&"
>>> re.sub(r'%..', lambda x: chr(int(x.group()[1:], 16)), VAR)
'/lkdMu9zkpE8w7UKDOtkkHhJlYZ6CaEaxqmsA+7G3e8=&'

Enjoy.

answered Sep 15, 2013 at 20:51

Ofir Israel

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1 Comment

My PM Over a year ago

Thank You Guys! I will try to get this to work and report back! Cheers!

Sérgio · Accepted Answer · 2013-09-15 20:48:12Z

1

var = "VAR=s2P0n6I%2Flonpj6uCKvYn8PCjp%2F4PUE2TPsltCdmA%3DRQPY%3D&"
var = var.replace("%2F", "/")
var = var.replace("%2B", "+")
var = var.replace("%3D", "=")

but you got same result with urllib2.unquote

import urllib2
var = "VAR=s2P0n6I%2Flonpj6uCKvYn8PCjp%2F4PUE2TPsltCdmA%3DRQPY%3D&"
var = urllib2.unquote(var)

answered Sep 15, 2013 at 20:48

Sérgio

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Comments

Patrick Collins · Accepted Answer · 2013-09-15 20:53:49Z

-1

This can't be done with a regex because there's no way to write any kind of conditional inside of a regex. Regular expressions can only answer the question "Does this string match this pattern?" and not perform the operation "If this string matches this pattern, replace part of it with this. If it matches this pattern, replace it with this. etc..."

answered Sep 15, 2013 at 20:53

Patrick Collins

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