Bash Shell Script Functions

Bash Shell Script Variables

Bash Shell Script Intro

Linux Operating Systems Overview

Mount ISO and Install FTP Client & Server

If ftp server not running in your Linux Box.

If you have ISO image. mount to local machine.


[root@localhost ~]# mount -o loop /home/ssankar/rhel-server-6.0-i386-dvd.iso /mnt/
[root@localhost ~]# cd /mnt/
[root@localhost mnt]#
[root@localhost Packages]# pwd
/mnt/Packages

Install FTP Client
----------------


[root@localhost Packages]# rpm -ivh ftp-0.17-51.1.el6.i686.rpm
warning: ftp-0.17-51.1.el6.i686.rpm: Header V3 RSA/SHA256 Signature, key ID fd431d51: NOKEY
Preparing...                ########################################### [100%]
   1:ftp                    ########################################### [100%]
[root@localhost Packages]# ftp
ftp> quit
[root@localhost Packages]# ftp localhost
Trying 127.0.0.1...
Connected to localhost (127.0.0.1).
220 (vsFTPd 2.2.2)

Install FTP  Server

----------------

[root@localhost Packages]# rpm -ivh vsftpd-2.2.2-6.el6.i686.rpm

warning: vsftpd-2.2.2-6.el6.i686.rpm: Header V3 RSA/SHA256 Signature, key ID fd431d51: NOKEY

Preparing...                ########################################### [100%]

   1:vsftpd                 ########################################### [100%]

[root@localhost Packages]#

[root@localhost Packages]# service vsftpd status

vsftpd is stopped

[root@localhost Packages]# service vsftpd start

Starting vsftpd for vsftpd:                                [  OK  ]

AWK Script Basic

[ssankar@localhost AWK]$ cat empdata.txt
1|100|sankar|dell|chennai
2|101|rahul|tcs|chennai
3|102|pal|cts|bangalore
4|103|kali|cts|bangalore
5|104|john|cts|bangalore
6|105|pal2|cts|bangalore
[ssankar@localhost AWK]$ cat sum.awk
BEGIN{
        FS="|"
        SNO=1 ;
        EMPID=2 ;
        NAME=3 ;
        COMPANY=4 ;
        LOCATION=5 ;
}
{
        list[$4] += 1;
        sum += $1 ;
}
END{
        printf ("%d\n", sum) ;

        for (comp in list)
        {
                printf("%s %d \n", comp, list[comp]);
        }
}
[ssankar@localhost AWK]$ awk -f sum.awk empdata.txt
21
tcs 1
dell 1
cts 4
[ssankar@localhost AWK]$

Bash shell script trap command example

#/bin/bash

#trace ctrl+c for kill a process
#trap handles seperately before terminating the process

function trap_handler()
{
        echo "trap_handler called  $$ $@"
        rm -f /tmp/input0.$$
        exit 1
}

trap trap_handler 2

echo "provide emp name"
read name

Bash shell script shift operation

#!/bin/bash

echo "passed arguments: $1 $2 $3.. array $@"
shift
echo "passed arguments: $1 $2 $3.. array $@"

declare -a arr=("sankar" "suriya" "pal" )

echo "length of array arr: ${#arr[@]}"

echo -e "$@"
shift 2

echo -e "$@"

echo "array ${arr[@]}"

Bash shell script shopt command sample

#!/bin/bash

## Before enabling xpg_echo
echo "welcome to\n"
echo "shell script training\n"
shopt -s  xpg_echo
## After enabling xpg_echo
echo "welcome to\n"
echo "shell script training\n"

# Before disabling aliases
alias l.='ls -l .'
l.

# After disabling aliases
shopt -u expand_aliases
l.

Bash shell script let command example

#!/bin/bash

#let command alter for expr command

let a=1
let b=2

let add=$a+$b
let sub=$a-$b
let mul=$a*$b
let div=$a/$b

echo $add $sub $mul $div

Bash shell script Set Unset Command Examples

#!/bin/bash

var="Learning Bash Shell Scripting"

set -- $var
echo "\$1=" $1
echo "\$2=" $2
echo "\$3=" $3
echo "\$4=" $4


echo "Var $var"

unset var

echo "After unset $var"

Bash shell script getops example

#! /bin/bash

#process the command line argument using getopts
#take action based on input

while getopts :h:r:l: OPTION
do
        case $OPTION in
        h)
                echo "help of $OPTARG"
                help "$OPTARG"
        ;;
        r)
                echo "Going to remove a file $OPTARG"
                rm -f "$OPTARG"
        ;;
        *)
                echo "Unknown option"
                echo "Usage: sh getopt.sh [-hrl] [value]"
        ;;
        esac
done

Bash shell script eval command

#!/bin/bash

#eval command - evaluate the expression and execute it
#provide input as username

if [ ! -z $1 ]
then
        proccomm="ps -e -o pcpu,cpu,nice,state,cputime,args --sort pcpu | grep $1"
else
        proccomm="ps -e -o pcpu,cpu,nice,state,cputime,args --sort pcpu"
fi
eval $proccomm

Bash shell script expressions

#!/bin/bash

#command line arg processing

#find last command line value [
echo "-1 value ${@: -1}"
echo "0th value ${BASH_ARGV[0]}"
echo "last index value ${@: $#}"
echo "final process value ${!#}"

for value in $@; do :; done
echo "after loop $value"

#]

#wildcards
#read the input, search that file from the directory

echo "enter the user name"
read user
echo "user $user"

#list files for user
for file in `ls /home/$user`
do
        echo "$file"
done

#list file extension .sh
for file in `ls /home/$user/Training/Shell*/*.sh`
do
        echo "$file"
done

#list file that has 3 char file name size
for file in `ls /home/$user/Training/Shell*/fo?`
do
        echo "$file"
done

#list files those start with [lfh]
for file in `ls /home/$user/Training/Shell*/[lfh]*`
do
        echo "$file"
done

#list files that matches the list
echo -e "\n a-z \r\n"
for file in `ls /home/$user/Training/Shell*/[a-z]*`
do
        echo "$file"
done


#arguments

echo "arguments $*"

Bash shell script functions

#!/bin/bash
#definition of function
#passing arg to function
#command line args
#exit status of function

#define your function here
Hello() {
        echo "Hello World"
}

#Invoke the function
Hello

#Passing the values
Hello() {
        echo "Hello World $1 $2"
}

#Invoke the function
Hello Sankar S

#return  values
Hello () {
        echo "Hello $1 $2"
        echo $@
        return 0
}

Hello Sankar Suriya
echo "Exit status of Hello Function : $?"

#command line arguments
numofarg=$#

echo "Total Number Of Arguments Are : $numofarg"

if [ $numofarg -gt 0 ]
then
        for i in $@
        do
                echo "print $i"
        done
fi

Bash shell script case statement

#!/bin/bash

n=11

case "$n" in

1)  echo "value 1 is received"
                ;;
2)  echo  "value 2 is received"
                ;;
3)  echo  "value is 3 received"
                ;;
10) echo  "value is 10 received"
                ;;
*) echo "number $n is not processed"
                ;;
esac

n="abc"

case "$n" in

"abc")  echo "value abc is received"
                ;;
2)  echo  "value 2 is received"
                ;;
3)  echo  "value is 3 received"
                ;;
10) echo  "value is 10 received"
                ;;
*) echo "number $n is not processed"
                ;;
esac


for filename in $(ls)
                                do
# Take extension available in a filename
                ext=${filename#*\.}
                case "$ext" in
                                c) echo "$filename : C source file"
                                ;;
                                o) echo "$filename : Object file"
                                ;;
                                sh) echo "$filename : Shell script"
                                ;;
                                txt) echo "$filename : Text file"
                                ;;
                                *) echo " $filename : Not processed"
                                ;;
                esac
done

Bash shell script looping statements

#!/bin/bash

#for loop , while loop

declare -a arr=( 1 2 3 4 5 )

echo ${arr[@]}

#< len of array

for (( i=0; i < ${#arr[@]} ; i++ ))
do
        echo "$i -> ${arr[$i]}"
done

#while loop

n=${#arr[@]}
i=0
while [ $i -lt $n ]
do
        echo "$i -- > ${arr[$i]}"
        let i++
done

#until
i=0
until [ ! $i -lt $n ]
do
        echo "$i -- > ${arr[$i]}"
        i=`expr $i + 1`
done

Bash shell script assignment operations

#!/bin/bash

#assignments

x=10
y=$x

echo "$x $y"

a=1.2
b=$a
echo "$a $b"

p="abc"
q=$p

echo "$p $q"

readonly n=100
s=$n

echo "$n $s"

#array to scalar

a=( 1 2 3 4 5 )
echo "${a[@]}"

m=${a[0]}
echo "a[0] $m"

arr=( "aa" "bb" "cc")
echo "${arr[@]}"

m=${arr[0]}
echo "arr[0] $m"

p=( "${arr[@]}" )

echo "p -> ${p[@]} "

v=100
a[2]=$v
echo "${a[@]}"

u="dd"
arr[1]=$u
echo "${arr[@]}"

Bash shell script if-else statements

#!/bin/bash

#if-else conditional statements

n=100
if [ $n -eq 100 ]
then
  echo "n is 100"
fi

n=99
if [ $n -eq 100 ]
then
  echo "n is 100"
else
          echo "n is not 100"
fi

n=99
if [ $n -eq 100 ]
then
  echo "n is 100"
elif [ $n -gt 100 ]
        then
          echo "n is greater than 100"
else
                  echo "n is less than 100"
fi


n=99
if [ $n -eq 100 ]
then
  echo "n is 100"
else
          if [ $n -gt 100 ]
                then
                    echo "n is greater than 100"
                else
                          echo "n is less than 100"
          fi
fi

Bash shell scripting Array Operations

#!/bin/bash

#array declarations and its operations

arr[0]='apple'
arr[1]='orange'
arr[2]='lemon'
arr[3]='kiwi'

a[0]=1
a[1]=2
a[2]=3
a[3]=4

echo "${arr[@]}"

echo "${arr[0]}"
echo "${arr[1]}"
echo "${arr[2]}"
echo "${arr[3]}"

echo "Total length of array : ${#arr[@]}"

echo "size of arr[0] : ${#arr[0]}"


#using declare

declare -a city=('Chennai' 'Trichy' 'Madurai' 'Kovai')
city=("${city[@]}" 'Villupuram' 'Vellore')

echo "${city[@]}"

#offset

echo "${city[0]:0:3}"


echo "${city[@]}"

#search and replace

echo "${city[@]/Chennai/Madras}"

#remove
unset city[0]

echo "${city[@]}"

#remove with pattern
declare -a newcity=( ${city[@]/*ai/} )

echo "${newcity[@]}"

#copy entire array to newone

mycitylist=("${newcity[@]}")

echo -e "my final city list: \n ${mycitylist[@]} "

#join arrays
total=("${newcity[@]}"  "${arr[@]}" "${a[@]}" )

echo "${total[@]}"

#delete entire array
unset total
echo "${total[@]}"

Bash shell scripting different variables

#!/bin/bash

#understanding different system and user varibles

echo "whoami $USER"

#global variables
# use ` for getting output of shell commands within echo output

#echo -e "Global Current Shell Values Are:\n `printenv`"

#user defined variables

i=10
j=20.5
k=30.254

echo "$i $j $k"

#strings

name="jataayu"
name1='jataayu'

echo $name $name1

echo '$name'

#constant

readonly n=100

echo $n

Shell Scripting Echo Examples

#!/bin/bash

echo "Hello World..!!"

printf "My First Shell Program\nAm after new line\n"

#-e enable interpretation of backslash escapes.
echo -e "Have Fun\nI love to Code\n"

#-n supresses the new line which is implicit when use echo command
echo -e -n "I dont introduce extra new lines\n"

Shell Scripting Arithmetic Operations

#!/bin/bash

#arithmetic operations

a=10
b=20

echo "a = $a b = $b"

val=`expr $a + $b`
echo "a + b : $val"

val=`expr $a - $b`
echo "a - b : $val"

val=`expr $a \* $b`
echo "a * b : $val"

val=`expr $b / $a`
echo "b / a : $val"

val=`expr $b % $a`
echo "b % a : $val"

readonly n=100

total=`expr $val + $n`

echo $total

#n=$total

#echo $n

#floating point arithmetic

x=10.1
y=20.2

echo "$x + $y" | bc
echo "$x - $y" | bc
echo "$x * $y" | bc
echo "$x / $y" | bc