Shell scripting question - incrementing

[Pietro Cerutti]

Paul Schmehl wrote:
> I could do this in perl easily, but I'm trying to force myself to learn
> shell scripting better.  :-)
> 
> I'm parsing a file to extract some elements from it, then writing the
> results, embeded in long strings, into an output file.
> 
> Here's the script:
> 
> cat file.1 | cut -d',' -f9 | sort | uniq > file.nicks
> 
> (read line; echo "alert ip \$HOME_NET any -> \$EXTERNAL_NET any
> (msg:\"JOIN $line detected\"; classtype:trojan-activity;
> content:\"JOIN\"; content:$line; sid:2000001; rev:1;)"; while read line;
> do echo "alert ip \$HOME_NET any -> \$EXTERNAL_NET any (msg:\"JOIN $line
> detected\"; classtype:trojan-activity; content:\"JOIN\"; content:$line;
> sid:2000001; rev:1;)"; done) < file.nicks > file.rules
> 
> The result is a file with a bunch of snort rules in it (I can't provide
> the actual data because it's sensitive.)
> 
> The rules look like this:
> alert ip $HOME_NET any -> $EXTERNAL_NET any (msg:"JOIN "channel"
> detected"; classtype:trojan-activity; content:"JOIN"; content:"channel";
> sid:2000001; rev:1;)
> alert ip $HOME_NET any -> $EXTERNAL_NET any (msg:"JOIN "channel2"
> detected"; classtype:trojan-activity; content:"JOIN";
> content:"channel2"; sid:2000001; rev:1;)
> 
> Once this file is created (or ideally *while* it's being created!) I
> need to increment the sid numbers.  The first one is 2000001.  The
> second needs to be 2000002, and so forth.   I don't know the total
> number of lines ahead of time, but it's easy enough to get after the
> file is created.  (wc -l file.rules | awk '{print $1}')
> 
> Is there a way to do this in shell scripting?  In perl I'd use a for
> loop and vars, but I'm not sure how to solve this problem in shell
> scripting.
> 
> In pseudo code I would do:
> 
> COUNT=`wc -l file.rules | awk '{print $1}'`
> LAST_SID=$((2000000 + COUNT))
> for (i=2000001; i >= ${LAST_SID}; i++) {
>    sed 's/2000001/${i}/g < file.rules > rules.new'
> }
> 

for i in `jot $COUNT 2000001`; do
  # foo bar
done


-- 
Pietro Cerutti

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