Re^3: Reliable way to detect base64 encoded strings

in reply to Re^2: Reliable way to detect base64 encoded strings
in thread Reliable way to detect base64 encoded strings

It's actually really straightforward.

Start of input
Followed by any number of groups of 4 characters from [A-Za-z0-9+/],
Followed by one of the following:
- [always matches]
- Four characters where
  - The first and second match /[A-Za-z0-9+/]/
  - The third matches /[AEIMQUYcgkosw048]/
  - The fourth is a "="
- Four characters where
  - The first matches /[A-Za-z0-9+/]/
  - The second matches /[AQgw]/
  - The third and fourth are both a "="
Followed by the end of input

It's probably a bit simpler after the update I just did for you:

Start of input
Followed by any number of groups of 4 characters from [A-Za-z0-9+/],
Followed by zero or one of the following:
- Four characters where
  - The first and second match /[A-Za-z0-9+/]/
  - The third matches /[AEIMQUYcgkosw048]/
  - The fourth is a "="
- Four characters where
  - The first matches /[A-Za-z0-9+/]/
  - The second matches /[AQgw]/
  - The third and fourth are both a "="
Followed by the end of input

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Re^4: Reliable way to detect base64 encoded strings by Rodster001 (Pilgrim) on Jun 29, 2009 at 22:57 UTC
Your explanation makes it very clear... thanks again!	[reply]
Re^4: Reliable way to detect base64 encoded strings by hahngoldn (Initiate) on Apr 15, 2010 at 22:22 UTC
Regex are not my favorite part of Perl....even if they are powerful. I'm trying to use your way to detect if a string is base64...so I was taking what you had and putting an if around it. I'm sure I'm just not getting it....could you give me some pointers? `if($string_whole =~ m / ^ (?: [A-Za-z0-9+/]{4} )* (?: [A-Za-z0-9+/]{2} [AEIMQUYcgkosw048] = \| [A-Za-z0-9+/] [AQgw] == )? \z /x ) $&Log ("it found base64-$i");` [download] Thanks in advance for your expertise.	[reply] [d/l]
Re^5: Reliable way to detect base64 encoded strings by ikegami (Patriarch) on Apr 16, 2010 at 05:05 UTC
You have the right idea, but `if (...) $&Log ("it found base64-$i");` [download] is not valid Perl. You want `if($string_whole =~ m/ ^ (?: [A-Za-z0-9+/]{4} )* (?: [A-Za-z0-9+/]{2} [AEIMQUYcgkosw048] = \| [A-Za-z0-9+/] [AQgw] == )? \z /x) { Log("$string_whole is valid base64"); }` [download]	[reply] [d/l] [select]
Re^6: Reliable way to detect base64 encoded strings by hahngoldn (Initiate) on Apr 16, 2010 at 22:49 UTC
when I use it as you have it I get `Unmatched [ in regex; marked by <-- HERE in m/ ^ (?: [ <-- HERE A-Za-z0-9+/ at C:\aaa\aeh_pop.pl line 153.` [download] I thought I was getting a problem with the regex...not the IF....but I didn't copy this in because i figured it was something I was doing. I see matched brackets... I tried to pull up into one line thinking the white space was giving issues...that didn't help. Thanks.	[reply] [d/l]
Re^7: Reliable way to detect base64 encoded strings by ikegami (Patriarch) on Apr 17, 2010 at 04:23 UTC
Re^8: Reliable way to detect base64 encoded strings by Anonymous Monk on Apr 30, 2010 at 19:10 UTC
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