Stupid Shell Tricks

Shell invocation

/bin/sh

-u - treat the use of unset variables as errors.
-x - show me execution.

pwgen

pwgen -B -c -n -y

• unabiguous
• 1 capital
• 1 number
• 1 special char

HTTP response codes - filter

tail -f /var/log/httpd/access | awk '$9 !=200'

the print is implied, $9 happens to be where the http response code is in my log: 200 means OK, so it's show me the NOT OK stuff.

Disk usage report

du -x --max-depth=1 / | sort  -rn

shell var of NOW

NOW=`date +%a.%d.%b.%Y`

fake_tomcat.sh

ARGV="$@"
if [ "x$ARGV" = "x" ] ; then
        echo usage: all start, stop, reload, abort, flush, or check
        exit
fi

case $# in
0)      echo 'Usage: ./snapshot <CPE name> (ie, ./snapshot YCDECUBC)' 1>&2; exit 2
esac

trap 'echo "";exit 3' 2 15
trap 'echo fake_tomcat.sh caught 1 HUP \-\> ok bye\! ; exit 3' 1
trap 'echo fake_tomcat.sh caught 3 QUIT \-\> ok bye\! ; exit 3' 3
trap 'echo fake_tomcat.sh caught 9 KILL \-\> ok bye\! ; exit 3' 9
trap 'echo fake_tomcat.sh caught 15 TERM \-\> ok bye\! ; exit 3' 15

TMPFILE=`mktemp /tmp/$0.XXXXXX` || exit 1

To move/duplicate filesystems I have a favorite way to do it locally:
# cd $filesystem_to_duplicate
# find . -print | cpio -pvdm /mnt

...where /mnt is the new filesystem/slice.
To duplicate/move across the network do it like this:
# cd $filesystem_to_duplicate
# tar cf - . | ssh otherhost "cd /$new_filesystem ; tar xf -"

function waitfor {
        if [ $# -lt 1 ] ; then
                echo "nothing to wait for"
        else
                echo "ok I'll wait"
                echo Still running = 1
                STILL_RUNNING=1
                while [ $STILL_RUNNING -gt 0 ]
                        do
                        STILL_RUNNING=`ps -auwwwx | grep $1 | grep -v grep | wc -l`
                        echo STILL_RUNNING = $STILL_RUNNING
                        sleep 1
                        echo waiting...
                        done
        fi
        echo $1
}
| tr '\n' ','


TimerOn()
{
  sleep $TIMELIMIT && kill -s 14 $$ &
  # Waits 3 seconds, then sends sigalarm to script.
}

Int14Vector()
{
  answer="TIMEOUT"
  PrintAnswer
  exit 14
}

trap Int14Vector 14

While loops for Fun and Profit

this script runs until you stop it. It collects file handle usage on a server putting the results in a file in the form:

<timestamp> <total allocated> <free> <maxpossible>

the last three field are from the /proc fs:

3391    969     52427
|	 |       |
|	 |       |
|       |       maximum open file descriptors
|        total free allocated file descriptors
total allocated file descriptors
(the number of file descriptors allocated since boot)

scripts:

while true;
do
 echo `date +%s` | awk 'BEGIN{ORS=""}{print $0 " "}' >> /home/dathornton/s4.t55.file-nr.2008040300;
 cat /proc/sys/fs/file-nr >> /home/dathornton/s4.t55.file-nr.2008040300;
 sleep 5;
done

You MUST MUST MUST put the sleep in there or "Bad Things Will Happen"(tm).

or in one line:

while true; do echo `date +%s` | awk 'BEGIN{ORS=""}{print $0 " "}' >> /home/dathornton/servername.file-nr.2008040300; cat /proc/sys/fs/file-nr >> /home/dathornton/servername.file-nr.2008040300; sleep 5; done

Traps

#!/bin/bash
# traptest.sh

trap "echo Booh!" SIGINT SIGTERM
trap "echo Kill" SIGKILL
echo "pid is $$"

while: # This is the same as "while true".
do
 sleep 5 # This script is not really doing anything.
done

Sorting Hostnames

service<instance>.location<instance>.fart.gas.bum

sort -t . -k2.2,1.1n -k1n

Sorting Ip Addresses

By Last three octets:

sort -t . -k 2,2n -k 3,3n -k 4,4n serverlist| more

epoch

#!/bin/sh
date -d "1970-01-01 UTC $1 seconds"

disable bash bell

echo "set bell-style none" >> ~/.inputrc

Awk

show me lines that don't have that in field 2

awk ' $2 !~ "[A-Za-z]" {print $0}'

who me lines that have less than 2 field:

awk ' NF < 2 {print $0}'

or shorter:

awk 'NF<2'