Shell scripting question - incrementing

Derek Ragona derek at
Tue Feb 19 18:42:10 UTC 2008

At 11:35 AM 2/19/2008, 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 >'

Similar to what other's have offered:

for i in `cat file.rules`;do
         sed 's/2000001/${i}/g >>;


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