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I wrote a little Bash script which accepts two values -- sender address and recipient address -- and finds any instances of mail sent from sender to recipient in /var/log/maillog. The script works fine, but it seems to be very inefficient. I'm just wondering how I can optimize it.
Code:
#!/bin/bash
SENDER="$1"
RECIPIENT="$2"
if [ "$#" -ne 2 ]; then
echo "Usage: findmail SENDER RECIPIENT"
exit 1
fi
# grab the message IDs of all messages where the SENDER is matched
MSG_ID=$(grep "from=<$SENDER" /var/log/maillog | cut -f4 -d":" | grep -v NOQUEUE)
for i in $MSG_ID; do
# for each message ID where SENDER is matched, see if RECIPIENT is also matched
if grep $i /var/log/maillog | grep "to=<$RECIPIENT" > /dev/null; then
# if the recipient is also matched, grep out all instances of the message ID
echo FROM $SENDER TO $RECIPIENT, ID $i
echo ----------
zgrep $i /var/log/maillog
echo ----------
fi
done
Again, it seems to work fine, but the script greps through /var/log/maillog three times -- first to find the sender; second to see if it's also going to the desired recipient; finally to view all instances of the message ID in the logs. This seems redundant and inefficient.
I currently don't have a good maillog to sample around with, but what you can do is a single grep that catches multiple lines, store that in one variable and grep on the recipient; that way you run through /var/log/maillog some fewer times;
In fact you're running through /var/log/maillog more than three times: first to find all the times "sender" matches, then for each sender all recipients to see if they're matched and finally you even use zgrep to uncompress if needed;
You could go somewhere along these lines:
Code:
msg_id=$(grep -A 5 "from=<${SENDER}" /var/log/maillog | grep -B 5 -A 5 "to=<$RECIPIENT" | head -n 1 | cut -d ':' -f 4 | grep -v NOQUEUE)
for i in $msg_id; do
echo FROM $SENDER TO $RECIPIENT, ID $i
zgrep $i /var/log/maillog
done
Above code is not very optimized, but you reduce the amount of times you have to go through /var/log/maillog quite a bit as you only have messages where sender and recipient match. Above code could not be completely correct, but I think you can fiddle around to get things right. (The second grep I did with before and after in such a way that the grep -A you began with is at that point still complete, so you can head the first line and get the appropriate field for message id from the first line)
grep "from=<$SENDER" /var/log/maillog | cut -f4 -d":" | grep -v NOQUEUE
for i in $MSG_ID; do
# for each message ID where SENDER is matched, see if RECIPIENT is also matched
if grep $i /var/log/maillog | grep "to=<$RECIPIENT" > /dev/null; then
# if the recipient is also matched, grep out all instances of the message ID
echo FROM $SENDER TO $RECIPIENT, ID $i
echo ----------
zgrep $i /var/log/maillog
echo ----------
fi
the above lines can be shortened to just one process
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