Advanced Bash-Scripting Guide

Today I want to recommend an excellent manual on programming ofadvanced bash shell.


These are the links :


(html version) http://www.tldp.org/LDP/abs/html/
(pdf version) http://www.tldp.org/LDP/abs/abs-guide.pdf


Stay tuned

Bash shell script to see who is logged on or logged out every 3 seconds

Today a simple bash shell script to check every 3 seconds what user is logged in or logged out.
This script use "who" linux/unix command, result of these command is saved on a file that is checked every 3 seconds with new who execution :


#!/bin/bash
# + Giovanni Palleschi
# + 05/30/2012 13:23
# + Who is logged on or logged out every 3 seconds
echo 'The current time is:'
date
echo ' '
# List Current Users Connected
echo 'The current users are:'
who | cut -d' ' -f1 | sort -u > ./list_user_before
cat ./list_user_before
# Loop control login - logout every 3 seconds
while [ 1 ]; do
   sleep 3
# List Current Users Connected
   who | cut -d' ' -f1 | sort -u > ./list_user_after
# List of New Users Connected
   echo ' '
   diff ./list_user_before ./list_user_after | grep "^>" | cut -d' ' -f2 |
   while read new_user_login
   do
     echo 'User' $new_user_login 'has logged in.'
     echo ' '
   done
# List of Users Disconnected
   diff ./list_user_before ./list_user_after | grep "^<" | cut -d' ' -f2 |
   while read new_user_login
   do
     echo 'User' $new_user_login 'has logged out.'
     echo ' '

   done

   tot_users_diff=$(diff ./list_user_before ./list_user_after | wc -l)

   if [ $tot_users_diff -eq 0  ]; then

     echo 'No user has logged in/out in the last 3 seconds.'

   fi

# Move file list user after in file user before  for next control

   mv -f ./list_user_after ./list_user_before

done

Stay tuned.

Ksh script to remove shared memory

Today a simple script to remove shared memory in ksh :


#!/bin/ksh


#
# Shell Script to remove shared memory MVNO Instance
#


PID=$(ipcs -m | grep 0x000000a[0-9a-b] | awk '{print $2}'|xargs)
for one_pid in ${PID}; do
    ipcrm -m ${one_pid}
    echo 'Removed shm : ' ${one_pid}
done

This script remove all shared memory from address 0x000000a0 to 0x000000ab. You must modify this expression to remove another shared memory.

Stay tuned.

Arithmetic calculation on real numbers in Ksh Script

Today a simple program to execute arithmetic calculation with ksh script :

#!/bin/ksh

echo "Enter the Price of the item \$ \c"

read price

echo "What Percentage of discount is available \c"

read per

echo "Your Total Savings are \c"

sav=`echo "scale=3\n(($price * $per) / 100)" | bc -l`

echo $sav

Is important see this command :

sav=`echo "scale=3\n(($price * $per) / 100)" | bc -l`

With "scale=3" we are fixing number of decimals to print.
With "bc -l" we are calculating with unix command bc the discout applied, with ($price * $per) / 100.

Stay tuned.

Dice simulator

Today a simple shell script to simulate rolls of two dices :

#!/bin/ksh

fc=1

while [ fc -eq 1 ]; do

clear

echo ' How many rolls : \c'

read times

ind=1

while [ $ind -le $times ]; do

echo 'Roll Dice ' $ind

dice1=$RANDOM

dice2=$RANDOM

echo 'dice1 :' $(( dice1%6+1 ))

echo 'dice2 :' $(( dice2%6+1 ))

ind=$(( $ind + 1 ))

done

echo ' Continue(y/n) : \c'

read ans

if [ $ans = 'N' ] || [ $ans = 'n' ]; then

fc=0

fi

done

Stay Tuned.

Awk

Hello everyone

Today i want share a good awk tutorial :

http://www.grymoire.com/Unix/Awk.html

Stay tuned.

Substring variable length record with awk.

The daily problem is this : I must print from third field to end of all records in a file where fields are separated from Tab character.

To resolve this problem i use awk in this way :

cat | awk -F" " '{ printf "%s\n",substr($0,index($0,$3)) }'

Where in -F awk option I specify tab character, and I use substr with index function of third field in each record read.

Stay tuned.