Shell Programming and Scripting

Hi Guys,

writing a small shell script, i need to convert parts of a string to "Hex". The problem is that it is not the full string that needs to be converted.
I think it's best to show an example:

$astring = "xxxxxx ABC+10+##########+DEF xxxx"

This is only an example to show how the string could look like. There can be many characters at the beginning, then there is a "starting code" ABC, a value which say's how long the element it (10 in this case), then the some unprintable hex characters (just marked as #) and the "end mark" DEF.

As the hex char's are not displayable, they should be displayed as "\x39" for example. So the above string should result in

$astring = "xxxxxx ABC+10+\x39\x55\x12\x84\xA7\x9F\x2C\xB1\xFF\x12+DEF xxxx"

after the conversion.

The only thing i can do is to loop through the string, find "ABC", get the count number and do the conversion.

Or is there a quicker and simpler solution you could think of?


Thanks a lot for your help !!!

Hans

have you tried

Code:

od -x or od -h

command?

od is converting a whole file. What i need is something that converts only parts of a string.

if od is doing what you want then extract the part of the string using sed/awk or anyother command and pass it through od and replace it back..

If that string can contain arbitrary binary data, you may have problems. Many UNIX utilities (sed, awk, sh, etc ...) are designed to read text files. Text files are not expected to contain control characters and nullbytes. Nullbytes (\0) in particular could cause failure since UNIX text tools often rely on the c library's string handling functions, which use \0 as a terminator.

Regards,
Alister

OK, this was a pain in the neck, but it - mayhap not too elegantly - will solve the problem given. It assumes hexdump to be installed, adapt to od if need be. You need an awk- program- file

Code:

$ cat awkfile
BEGIN{FS="+"; hd="hexdump -v -e '\"\\\\\" /1 \"X%02X\"'" }
        {for (i=1; i<=NF; i++)
                {if ($i~"ABC") {j=i+2}
                 if (i==j) {printf "%s",$i|hd;printf "%s", FS} else printf "%s%s", $i,FS}}

And then, execute that:

Code:

echo $astring|awk -f awkfile
xxxxxx ABC+10+\X39\X55\X12\X84\XA7\X9F\X2C\XB1\XFF\X12+DEF xxxx+

I know, there is an field separator too many at the end, but I'm out of patience now...

Code:

perl -pe '$p=qr/ ABC\+([^+]+)\+/; /$p/; s/($p)(.{$1})/$1.join("",map{"\\x$_"}unpack("H2"x$2,$3))/e' file

Regards,
Alister

---------- Post updated at 11:02 PM ---------- Previous update was at 10:54 PM ----------

Been there myself many times. Unfortunately, your solution won't work reliably. The timing of hexdump's output and awk's output isn't in anyway guaranteed.

With a 3 line sample file and stdout a terminal, the hexdump output for all three lines shows up after all of awk's output for those three lines.

With the same sample file and stdout redirected to a file, the hexdump output for all three lines occurs in the middle of the first line of awk output.

I'm almost certain that the consistent difference is a side effect of my awk implementation increasing buffering in the absence of interactivity.

Regards,
Alister