Bash Cheatsheet Index:
Remove whitespace:
$ echo 'foo - bar' | tr -d '[:space:]'
foo-bar
Convert to uppercase:
$ echo 'HeLLo' | tr '[:lower:]' '[:upper:]'
HELLO
Use iptables to block all bad ip addresses:
$ cat /var/log/maillog | grep 'lost connection after AUTH from unknown' | tail -n 5
May 10 11:19:49 srv4 postfix/smtpd[1486]: lost connection after AUTH from unknown[185.36.81.145]
May 10 11:21:41 srv4 postfix/smtpd[1762]: lost connection after AUTH from unknown[185.36.81.164]
May 10 11:21:56 srv4 postfix/smtpd[1762]: lost connection after AUTH from unknown[175.139.231.129]
May 10 11:23:51 srv4 postfix/smtpd[1838]: lost connection after AUTH from unknown[185.211.245.170]
May 10 11:24:02 srv4 postfix/smtpd[1838]: lost connection after AUTH from unknown[185.211.245.170]
Get the data to show only IPs:
cat /var/log/maillog | grep 'lost connection after AUTH from unknown' | cut -d'[' -f3 | cut -d ']' -f1 | tail -n5
185.36.81.164
175.139.231.129
185.211.245.170
185.211.245.170
185.36.81.173
Get the uniqe IP addresses:
$ cat /var/log/maillog | grep 'lost connection after AUTH from unknown' | cut -d'[' -f3 | cut -d ']' -f1 | sort | uniq
103.194.70.16
112.196.77.202
113.172.210.19
113.173.182.119
139.59.224.234
Redirect the output to iptables:
$ for ip in $(cat /var/log/maillog | grep 'lost connection after AUTH from unknown' | cut -d'[' -f3 | cut -d ']' -f1 | sort | uniq); do iptables -I INPUT -s ${ip} -p tcp --dport 25 -j DROP; done
if [[ $# -eq 0 ]] ; then
echo 'need to pass args'
exit 0
fi
if [ $1 == "one" ] || [ $1 == "two" ]
then
echo "argument 1 has the value one or two"
exit 0
else
echo "I require argument 1 to be one or two"
exit 1
fi
or:
NAME=${1}
if [ -z ${NAME} ]
then
echo NAME is undefined
exit 1
else
echo "Hi ${NAME}"
fi
if [ -z ${OWNER} ] || [ -z ${NAME} ]
then
echo "does not meet requirements of both environment variables"
exit 1
else
echo "required environment variables exists"
fi
set -ex
count=0
echo "boot"
ping localhost &
while [ $count -le 5 ]
do
sleep 1
count=$((count + 1))
echo $count
done
ps aux | grep ping
echo "tear down"
kill $!
sleep 2
UPDATE_COMPLETE=false
UPDATE_STATUS=running
COUNT=0
while [ ${UPDATE_COMPLETE} == false ]
do
if [ $count -gt 10 ]
then
echo "timed out"
exit 1
fi
if [ ${UPDATE_STATUS} == running ]
then
echo "still running"
sleep 1
COUNT=$((COUNT+1))
if [ $count == 7 ]
then
UPDATE_COMPLETE=true
fi
elif [ ${UPDATE_STATUS} == successful ]
then
UPDATE_COMPLETE=successful
else
echo "unexpected update response"
exit 1
fi
done
echo "complete"
for i in $(ls | grep .tar): do
docker load -i $i;
done
message(){
NAME=${1}
echo "Hi ${NAME}"
}
or pass all args:
message(){
echo "Hi $@"
}
Redirect stderr to /dev/null:
grep -irl faker . 2>/dev/null
Redirect stdout to one file and stderr to another file:
grep -irl faker . > out 2>error
Redirect stderr to stdout (&1), and then redirect stdout to a file:
grep -irl faker . >out 2>&1
Redirect both to a file:
grep -irl faker . &> file.log
$ STRING="abcdefghij"
$ echo ${STRING:3}
defghij
With tail to only show the last 3 characters:
$ STRING="abcdefghij"
$ echo ${STRING} | tail -c 4
hij