Replace Bytes in File between Value X and Y with Z

Replace Bytes in File between Value X and Y with Z - Printable Version

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Replace Bytes in File between Value X and Y with Z - lastyle - Feb-04-2020

Hi all

I`ve got a File that contains different Byte Values and i need some of them to be exchanged.

Idea is to read the entire File into an Array and then using a routine like :

If byte Value is between 193 and 219 then substract 129 from it and replace with the new Value in the array.

Open File and after exchange that is plain Simple, but how would a Function like this look like ?

Thanks for any Help guiding me there Smile

RE: Replace Bytes in File between Value X and Y with Z - Larz60+ - Feb-04-2020

What have you tried so far?

RE: Replace Bytes in File between Value X and Y with Z - lastyle - Feb-04-2020

(Feb-04-2020, 06:35 PM)Larz60+ Wrote: What have you tried so far?

to be honest, nothing. I dont know which function i should use for a compare between value x and y

In vb.net i am more experienced and would parse like

Public Sub parsefile(filename As String)
Dim bytes As Byte() = System.IO.File.ReadAllBytes(filename)
For i = 0 To bytes.length
if val(bytes(i)) > 193 < 219 then
val(bytes(i)) = val(bytes(i))-129
Next i
End Sub

But here with python i have no idea, thats why i am hoping somebody would help me

RE: Replace Bytes in File between Value X and Y with Z - Larz60+ - Feb-04-2020

looks like you need to start with a python tutorial, I'll list a couple of good ones below.
I will show examples for:

variables -- in python don't have to be declared before use as in Virtual basic
x = value

opening and reading filename -- is simple
with open(filename, mode) as name:

        for line in name:
            line = line.strip() # removes whitespace
            ...

A text line can be parsed into a list:
```
   words = line.split()
```
iterate through list:
```
    for word in listname:
        ...
```
Get numeric value of letter:
```
   val = ord(word[index])
```
to get letter from numeric:
```
   letter = chr(val)
```
print any variable:
```
   print(val, letter)
```

formatted print

   print(f"value of val: {val}, letter: {letter}")

val, letter, x are variables, don't need to be declared

These are both excellent tutorials:
How to Think Like a Computer Scientist: Interactive Edition
Python3 Tutorial