Incrementing with a twist - please help


 
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# 1  
Old 03-03-2010
Incrementing with a twist - please help

I'm currently trying to write a ksh or csh script that would change the name of a file found in directories and attach to the name an incrementing three digit number.
I know how to write a script that will go:
000, 001, 002, 003, etc

The twist is I need more increments then allowed by a 3 digit number so I want to use letters too. For example:
008, 009, 00A, 00B, 00C --- 00Z, 010, 011, 012, 013 --- 099, 0AA, 0AB --- 0ZZ, 100, 101, etc

Any slick ways of doing this? I searched for it but couldn't find anything like this on the forum.

Thanks!

Rust
# 2  
Old 03-03-2010
Code:
digits='0,1,2,3,4,5,6,7,8,9,A,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z'
for i in $(eval echo {$digits}{$digits}{$digits}); do echo $i; done



---------- Post updated at 02:34 AM ---------- Previous update was at 02:25 AM ----------

By the way, your example sequence is inconsistent. 09A and 09B should follow 099, not 0AA and 0AB. Smilie

Regards,
Alister
# 3  
Old 03-03-2010
Code:
#!/usr/bin/perl

for $i  ( 000 .. 999 ) {
  if ($i < 10 ) {
    $int="00".$i
}
 elsif (( $i >= 10 ) && ( $i < 100 )){
     $int="0".$i
    }
 else {
  $int=$i;
   }

  for $j  ( A .. Z ){
  print "$int$j\n"
}
}

cheers,
Devaraj Takhellambam
# 4  
Old 03-03-2010
Thanks for you help guys. And your right Alister, I was off on my example. Smilie

Going to test it now.
# 5  
Old 03-04-2010
alister's script is best. Can you explain why "eval" can generate the data automatically?

Code:
$ eval echo {$digits}{$digits}{$digits} |more
000 001 002 003 004 005 006 007 008 009 00A 00B 00C 00D 00E 00F 00G 00H 00I 00J 00K 00L 00M 00N 00O 00P
....

Here is my code.
Code:
digits='0 1 2 3 4 5 6 7 8 9 A B C D E F G H I J K L M N O P Q R S T U V W X Y Z'
for i in ${digits}
do
  for j in $digits
  do
    for k in $digits
    do
       echo "$i$j$k"
    done
  done
done

# 6  
Old 03-04-2010
Hi, rdcwayx

It's not the eval which generates the data; it's brace expansion.

Code:
#Non-numeric example
$ echo f{ee,i,o,um}
fee fi fo fum

#Numeric example
$ echo {0,1}{0,1}{0,1}
000 001 010 011 100 101 110 111

Since the original poster's problem requires a fairly long sequence of digits, for brevity I wanted to avoid:
Code:
echo {0,1,2,3,4,5,6,7,8,9,A,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z}{0,1,2,3,4,5,6,7,8,9,A,B,C,D,E,F,G,H,etc.....

Storing the list in the variable $digits allows me to do that. However, since brace expansion occurs before variable expansion, we need to send the command line through the shell's parser a second time, using eval. Otherwise we just get:
Code:
$ digits=0,1
$ echo {$digits}{$digits}{$digits}
{0,1}{0,1}{0,1}

Instead of:
Code:
$ eval echo {$digits}{$digits}{$digits}
000 001 010 011 100 101 110 111

Note: Brace expansion does not occur if there is no unquoted comma within the braces, so we do not need to quote {$digits}.

A downside to this approach is that if the list of digits is long enough, or if there are many braced terms to expand, the list of resulting words could exceed the command line length limit. In such a case, your approach is superior as it never needs to execute a long command line. Another way around this limitation would be to write it out explicitly in the for loop:
Code:
$ for i in {0,1}{0,1}{0,1}; do echo $i; done
000
001
010
011
100
101
110
111

IMPORTANT: Brace expansion is not a posix-standardized feature, so if that's a concern, my approach is not an option; yours would be the better choice. Also, the order of brace expansion in relation to parameter expansion as described above is BASH specific (which I chose to use for the illustrative examples since it's much more popular than ksh, and because for this particular scenario it's the more complicated case). In pdksh, ksh88, and ksh93, brace expansion occurs after parameter expansion, not before. So, if using a ksh variant, neither the eval nor the echo nor the command substition is necessary (though in this case their presence does not affect the end result); a simple 'for i in {$digits}{$digits}{$digits}' would be sufficient.

Hope that helps. If not, feel free to ask for clarification.

Cheers,
Alister

Last edited by alister; 03-04-2010 at 10:44 AM..
# 7  
Old 03-04-2010
Thank you so much for the explanation.

One question for Moderators,

I try to give bits awards to alister's reply, but my ID can't do that now.

I remember I can give before. Can you help?
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