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Find and increment value in string of hex

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Top Forums Shell Programming and Scripting Find and increment value in string of hex
# 8  
Old 12-19-2017
Sorry typo...should have said
Code:
0x7F

(corrected it now)

So all values greater than this, starting with
Code:
0x80

will be represented as 4 digits and the length set to 02, i.e.
Code:
84020080a7

# 9  
Old 12-19-2017
Try
Code:
awk '
        {while (match ($0, /84[^a]*a7/))        {printf "%s", substr ($0, 1, RSTART + 1)
                                                 if (TMP == "") TMP = sprintf ("%.f", "0x" substr ($0, RSTART + 4 , RLENGTH - 6))
                                                   else         TMP++
                                                 LG = (TMP > 127) + 1
                                                 printf "%02x%0*x", LG, 2*LG, TMP
                                                 $0 = substr ($0, RSTART + RLENGTH - 2)
                                                }
         print $0
        }
' file

Be aware that with lines longer than the system config parameter LINE_MAX (my system: 2048) the result may not be what you expect.
# 10  
Old 12-19-2017
Hi securegooner,
If you increment 7F to 80 and on subsequent runs to 81, 82, 83, and 84; you then have an ambiguity as to where the string starting with 84 starts. Should the string 84017Fa7 be incremented to 84020080a7 or to 84020100a7??? And, can there only be values 01 and 02 after the leading 84? Or, should 8402FFFFa7 or 84027F7Fa7 be incremented to 8403010000a7?

And will you really have an uppercase 7F and a lowercase a7?

Please be very sure that your specification is clear and complete and accurately specifies what you are trying to do.

Hi RudiC,
Note also that using match($0,/84[^a]*a7/) may get a false match on even byte boundaries such as 0840a7 and RSTART and RLENGTH won't be set correctly for a cases like 08012aa7 and 08020a0aa7.

To get proper alignment, we have to be sure tha characters are matched in pairs starting on odd character boundaries.
This User Gave Thanks to Don Cragun For This Post:
RudiC
# 11  
Old 12-19-2017
Thanks Don, valuable caveats indeed, although I regarded my attempt more a proof of concept than a bullet proof program.
Eliminating false matches can be done by in the regex exactly counting the characters between 84 and a7, which could be 4 or 6 according to the spec in post#1. And, finding even boundaries equiv. to full bytes can be done by evaluating the evenness or oddness of RSTART. See below:
Code:
awk '
        {print
         while (match ($0, /84....(..)?a7/))    {printf "%s", substr ($0, 1, RSTART + 1)
                                                 if (RSTART%2)  {if (!TMP)      TMP = sprintf ("%.f", "0x" substr ($0, RSTART + 4 , RLENGTH - 6))
                                                                    else        TMP++
                                                                 LG  = (TMP > 127) + 1
                                                                 printf "%02x%0*x", LG, 2*LG, TMP
                                                                }
                                                        else    {RLENGTH--
                                                                 printf "%s", substr ($0, RSTART + 2, RLENGTH - 4)
                                                                }
                                                 $0 = substr ($0, RSTART + RLENGTH - 2)
                                                }
         print
        }
' file

I appreciate there's still some pitfalls that are not yet covered, but I think that's how far we get with a spec as given.
# 12  
Old 12-20-2017
Thanks very much for your comments and suggestions RudiC and Don.

I will try the posted code on my data to see if it produces the output I wanted to achieve and get back to you...
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