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awk decrement loop

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# 1  
Old 11-25-2012
Hammer & Screwdriver awk decrement loop
Hi all,

could you please help me - a complete newbie - with the following task. I have such data:

12345678

and i need to split it into all possible sequences of 4 chars, like this:

1234_5678

and then again:

1_2345_678
12_3456_78
123_4567_8

I can do this in GAWK

Code:
#c is the sequence length

BEGIN{FS=OFS="";o=" ";c=4;n="_";}

{ gsub( " ", ""); gsub( /./, "& ");

{  for (i = 0; ++i <=NF;) 
            if ($i == o)
            ++D % c || $i = n
} 1

Can i have another loop for 'c' inside this loop - to decrement it: --d till d=1?

Do you think AWK is OK for that task? I really want to have something native without the need to incorporate the code inside a shell script.

Thank you!
# 2  
Old 11-25-2012
Quote:
Originally Posted by shivacoder
Can i have another loop for 'c' inside this loop - to decrement it: --d till d=1?
Of course. Probably there are some limits to nesting loops, but i have to encounter them yet.

Quote:
Do you think AWK is OK for that task?
Absolutely. You could do the same in other languages too (perl, shell, python, ruby, ...), but it probably would gain you nothing. If you feel comfortable with awk (and it seems that you do) then, by all means, go with it!

I hope this helps.

bakunin
# 3  
Old 11-25-2012
Note that according to the standards, setting FS to an empty string produces undefined results. (Doing so treats each character as a field in gawk and some other version of awk, but generates various errors or unexpected results on other versions of awk.) If I understand what shivacoder is trying to do, I think the following is a portable way to do what was requested:
Code:
awk -v c=4 '{
        for(i = c; i >= 1; i--) {
                # Print a header preceded by a <newline> if this is not the 1st
                # output line.
                printf("%sProcessing %d character strings from \"%s\".\n",
                        i != c || NR > 1 ? "\n" : "", i, $0)
                if(i > length($0)) {
                        printf("There aren'\''t %d characters in \"%s\".\n",
                                i, $0) 
                        continue
                }
                # Print the 1st line.
                printf("%s%s%s\n", substr($0, 1, i),
                        i == length($0) ? "" : "_", substr($0, i + 1))
                if(length($0) >= i)
                        for(j = 1; j + i < length($0); j++)
                                printf("%s_%s_%s\n", substr($0, 1, j),
                                        substr($0, j + 1, i),
                                        substr($0, j + i + 1))
                # Do not print the last line if it would duplicate the 1st line.
                if(i != length($0) / 2 && length($0) > i)
                        printf("%s_%s\n", substr($0, 1, length($0) - i),
                                substr($0, length($0) - i + 1))
        }
}' input

Last edited by Don Cragun; 11-26-2012 at 01:18 AM..
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