Code¶

Decision Making¶

IF¶

Check File Type¶

#!/bin/bash

# check character divice files
if [ -c /dev/tty ]; then
    echo "yes '/dev/tty' is a character device"
fi

# check block divice files
if [ -b /dev/sda ]; then
    echo "yes '/dev/sda' is a block device"
fi

# check character divice files
# mkfifo /tmp/pipef
if [ -p /tmp/pipef ]; then
    echo "yes '/tmp/pipef' is a pipeline device"
fi

# check symbolic link files
if [ -h /usr/bin/java ]; then
    echo "yes '/usr/bin/java' is a symbolic link"
fi

# check symbolic link files
if [ -L /usr/bin/java ]; then
    echo "yes '/usr/bin/java' is a symbolic link"
fi

# check socket files
if [ -S /run/cups/cups.sock ]; then
    echo "yes '/run/cups/cups.sock' is a socket file"
fi

# check readable files
if [ -r /etc/passwd ]; then
    echo "yes '/etc/passwd' is a readable file"
fi

# check writable files
if [ -w /etc/passwd ]; then
    echo "yes '/etc/passwd' is a writable file"
fi

# check executable files
if [ -x /bin/bash ]; then
    echo "yes '/bin/bash' is a executable file"
fi

# check modifaction files
if [ -N /bin/bash ]; then
    echo "yes '/bin/bash' has been modified"
fi

# check SUID files
if [ -u  /usr/bin/passwd ]; then
    echo "yes '/usr/bin/passwd ' has s-user-id"
fi

# check SGID files
if [ -g /usr/bin/wall ]; then
    echo "yes '/usr/bin/wall' has s-group-id"
fi

# check sticky bite files
if [ -k /tmp ]; then
    echo "yes '/tms' has has active sticky bit"
fi

# check the file exists
if [ -e /etc/passwd ]; then
    echo "yes '/etc/passwd/' is exists"
fi

# check file exists and a directory
if [ -f /etc/passwd ];then
    echo "yes '/etc/passwd' is exists and also is a file"
fi

# check file exists and a directory
if [ -d /etc ];then
    echo "yes '/etc' is a file and also is a directory"
fi

# check file exists and readable
if [ -s /etc/passwd ];then
    echo "yes '/etc/passwd' is a file and also has content"
fi

# check file owner
if [ -O /etc ];then
    echo "yes '/etc' is for mehrdad"
else
    echo "no '/ect' for root"
fi

# check file group
if [ -G /etc ];then
    echo "yes '/etc' in mehrdad group"
else
    echo "no '/ect' in root group"
fi

if [ -f /etc/passwd ] || [ -r -x /etc/passwd ]; then
    echo "yes"
else
    echo "no"
fi

if [ ! -d /var/log ]; then
    echo "directory '/var/log' does not exist"
else
    echo "directory '/var/log' exists"
fi

Check Input Arguments¶

#!/bin/bash

if [ $# -ne 1 ]; then
    echo "your input arguments are not equel to 1"
    echo "usage: $0 start|stop|restart|status"
    exit 1
fi

if [ $1 = "start" ];then
    echo "going to start service..."
elif [ $1 = "stop" ];then
    echo "going to stop service..."
elif [ $1 = "restart" ];then
    echo "going to restart service..."
elif [ $1 = "status" ];then
    echo "going to status service..."
else
    echo "sub-commnad is not found."
    exit 1
fi

Is Integer?¶

#!/bin/bash

testuser=$1

# grep generate exit-code 0 if the condition is true
# if grep $testuser /etc/passwd; then
#     echo "user $testuser has been found"
# else
#     echo "user $testuser does not exists"
# fi

# ---

# if [ $testuser -eq 1 ]; then
#     echo "$1 is euqel with 1"
# elif [ $testuser -lt 1 ]; then
#     echo "$1 is less then 1"
# elif [ $testuser -gt 1 ]; then
#     echo "$1 is greather then 1"
# else
#     echo "false"
# fi

# ---

if [ $(echo "2>1" | bc) -eq 1 ]; then
    echo "yes"
else
    echo "no"
fi

Is String?¶

#!/bin/bash

testuser=mehrdad

if test $testuser = mehrdad; then
    echo "true"
else
    echo "false"
fi

# ---

str1 =  str2
str1 != str2
str1 < str1
str1 > str1
-n    check str if greater than zero
-z    check str if equal to zero

str1="A A"
if [ "$str1" = "A A" ]; then
    echo "true"
else
    echo "false"
fi

read -p "enter a name: " str
while [ -n $str ]   # OR while [[ $str != "" ]]
do
    echo "yes $str"
    read str
done

Switch Case¶

#!/bin/bash

user=$1

case $user in

"mehrdad")
    echo "mehrdad"
    ;;
"leila")
    echo "leila"
    ;;
"hamid")
    echo "hamid ghasemkhani"
    ;;
*)
    echo "oh nooo"
    ;;
esac

By Predefined Arguments¶

#!/bin/bash

if [ $# -ne 1 ]; then
    echo "your input arguments are not equel to 1"
    echo "usage: $0 start|stop|restart|status"
    exit 1
fi

case $1 in
start)
    echo "going to start service..."
    ;;
stop)
    echo "going to stop service..."
    ;;
restart)
    echo "going to restart service..."
    ;;
status)
    echo "going to status service..."
    ;;
*)
    echo "sub-commnad is not found."
    exit 1
    ;;
esac

Select¶

#!/bin/bash

PS3="Enter the value: "

select item in "option1" "option2" "exit"
do
    case $item in
    "exit")
        break
    ;;
    "option1")
        "option-1 is selected"
    ;;
    "option2")
        "option-2 is selected"
    ;;
    *)
        clear
        echo "wrong selection"
    ;;
    esac
done

#!/bin/bash

function diskspace() {
    clear
    df -kh
}

function whoison() {
    clear
    who
}

function memusage() {
    cat /proc/meminfo
}

function cpuinfo() {
    cat /proc/cpuinfo
}

PS3="Enter your command: "

commands=(cpuinfo meminfo diskinfo online_users exit)

select command in ${commands[@]}; do
    case $command in
    "meminfo")
        memusage
        ;;
    "cpuinfo")
        cpuinfo
        ;;
    "diskinfo")
        diskspace
        ;;
    "online_users")
        whoison
        ;;
    "exit")
        break
        ;;
    *)
        echo "wrong selection"
        ;;
    esac
done

#!/bin/bash

select lang in C Java Python Bash exit; do
    if [[ $lang = "exit" ]]; then
        exit 0
    fi
    echo "Hello $lang"
done

Loop Condition¶

For¶

#!/bin/bash

# C style
for ((c = 1; c <= 10; c++)); do
    echo "C is $c"
done

echo "---"

# python style
for p in {1..20..2}; do
    echo "P is $p"
done

echo "---"

# for in list
for color in red green blue; do
    echo "color is $color"
done

#!/bin/bash

# file as a list
lc=1
for line in $(tail -5 /etc/passwd); do
    username=$(echo $line | cut -d":" -f1)
    echo "$lc username: $username"
    lc=$(($lc + 1))
done

echo "---"

IFS=$'\n'
lc=1
for line in $(tail -5 /etc/services); do
    echo $lc $line | cut -d":" -f1
    lc=$(($lc + 1))
done

echo "---"

for f in /etc/*; do
    if [ ! -r $f ]; then
        echo "file $f is not readable"
    fi
done

echo "--- show hostname ips by type ---"

IPS=$(hostname -i)

for x in $IPS; do
    case $x in
    *"."*)
        echo "IPv4S $x"
        ;;
    *":"*)
        echo "IPv6 $x"
        ;;
    esac
done

#!/bin/bash

read -p "pleas enter a number: " no

for ((c = 0; c < no; c++)); do
    echo "Hello $c"
done

echo "---"

for count in $(seq 1 $no);do
    echo "Hi $count"
done

While¶

#!/bin/bash

count=10
while [ $count -ge 1 ]
do
  echo $count
  count=$[ $count - 1 ]
done

echo "---"

while read -n1 -r -p "choose Yes|No or e for exit " && [[ $REPLY != q ]]; do
  case $REPLY in
    y) echo "Yes";;
    n) echo "No";;
    e) exit ;;
    *) echo "What?";;
  esac
done

#!/bin/bash

answer=""
while [ "$answer" != "yes" ] && [ "$answer" != "no" ]; do
    echo "do you want to exit? yes|no "
    read answer
    answer=`echo $answer | tr [A-Z] [a-z]`
done

#!/bin/bash
while IFS= read -r line;do
    echo "**$line**"
done < <(ping google.com)

Break¶

#!/bin/bash

for var1 in {1..10}
do
    if [ $var1 -eq 5 ]; then
        break
    fi
    echo $var1
done

Continue¶

#!/bin/bash

for var1 in {1..10}
do
    if [ $var1 -gt 3 ] && [ $var1 -lt 8 ]; then
        continue
    fi
    echo $var1
done

$¶

Input Parameters¶

#!/bin/bash

echo "\$0 your script name is $0"
echo "\$1 your first parameter is $1"
echo "\$2 your second parameter is $2"

echo "\$# you entered $# input parameter"

echo "\$? current status code is $?"

echo "'\$*' is $*"
echo "'\$@' is $@"

Difference of `$@` & `$#`¶

#!/bin/bash

count=1
for params in "$*"
do
    echo "\$* parameters #$count = $params"
    count=$[ count + 1 ]
done

echo "---"

count=1
for params in "$@"
do
    echo "\$@ parameters #$count = $params"
    count=$[ count + 1 ]
done

Exec¶

exec-in¶

#!/bin/bash

exec 0< inputfile
count=1
while read line
do
    echo "Line #$count $line"
    count=$(( $count + 1 ))
done

exec-out¶

#!/bin/bash

exec 1> output
echo "1"
echo "2"
echo "3"
echo "4"
echo "5"
echo "6"
echo "7"

Check Exist Username¶

#!/bin/bash

if [ $# -ne 1 ];then
    echo "miss or more input argument!"
    echo "exact argument is one"
    exit 1
fi

query=`cut -d: -f1 /etc/passwd | grep -x "$1"`

if [ ${#query} -ne 0 ];then
    echo "user $1 has been found"
    exit 0
else
    echo "user $1 does not exitst"
    exit 1
fi

Basic Input¶

#!/bin/bash

echo -n "Enter your name: "
read name
echo "Hello $name"

Close File Descriptor¶

 #!/bin/bash

exec 3> output
echo "test line" >&3
exec 3>&-
echo "something..." >&3

#!/bin/bash

exec 1>&-
echo "something..."

Add Integers¶

#!/bin/bash

sum=0
if [ $# -ne 2 ];then
    echo "$0 is wrong! you must enter 2 number"
else
    sum=$[ $1 + $2 ] # other format sum=$(( $1 + $2 ))
    echo $sum
fi

Get Current working directory and Basename¶

Directory Basename¶

#!/bin/bash

basename $0
dirname $0

# /dir/name/basename.file

Print current directory¶

#!/bin/bash

script_dir="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
echo $script_dir

Print basename¶

#!/bin/bash

pd=`pwd`
bn=`basename $0`
dirname $0

echo "${pd}/${bn}"

Factorial¶

#!/bin/bash

fact=1
i=1
while [ $i -le $1 ]
do
    fact=$(($fact * $i))
    i=$(($i + 1))
done
echo "The factorial $1 is $fact"

Function¶

#!/bin/bash

function myFunc0 {
    echo ${1:-defualt} #set default value for function parameter
}

myFunc1() {
    echo ${3:=default}
    echo $#
    echo $1
    echo $2
    echo $3

}

function myFunc2 {
    echo "Hello Func 2"
}

myFunc3() {
    return 10
}

echo "function 0"
myFunc0

echo

echo "function 1"
myFunc1 mehrdad radin leila
myFunc1

echo

echo "function 2"
func_var=$(myFunc2)
echo $func_var

echo

echo "function 3"
myFunc3
echo $?

lsof¶

# testing lsof with file descriptors
touch testfile7
exec 3>testfile3
exec 6>testfile6
exec 7<testfile7
lsof -a -p $$ -d 0,1,2,3,6,7

Memory Alert¶

#!/bin/bash

# Method 1
total=$(free -m | head -n 2 | tail -n 1 | tr -s " " | cut -d" " -f2)
used=$(free -m | head -n 2 | tail -n 1 | tr -s " " | cut -d" " -f3)
free=$(free -m | head -n 2 | tail -n 1 | tr -s " " | cut -d" " -f4)

# Method 2
# totle=$(vmstat -s | grep "total memory" | tr -d "K total memory")
# used=$(vmstat -s | grep "used memory" | tr -d "K used memory")
# free=$(vmstat -s | grep "free memory" | tr -d "K free memory")

warning_area=$((total / 100 * 10))

echo $warning_area

if [ $used -gt $warning_area ]; then
    echo "upper 90%"
else
    echo "everythin is ok"
fi

Parameters Options¶

#!/bin/bash

while getopts ab:c opt; do
    case "$opt" in
    a) echo "found option -a" ;;
    b) echo "found option -b with parameter $OPTARG" ;;
    c) echo "found option -c" ;;
    *) echo "$0 --help" ;;
    esac
done

Read From File¶

# #!/bin/bash
count=1
cat /etc/passwd | while read line; do
    echo "Line $count: $line"
    count=$(($count + 1))
done

#!/bin/bash
count=1
while read line; do
    echo "Line $count: $line"
    count=$(($count + 1))
done < /etc/passwd

Redirection Priority¶

#!/bin/bash

exec 3>&1
exec 1> output
echo "Line 3"
echo "Line 4" >&3
exec 1>&3
echo "normal"

Shift Over Option¶

#!/bin//bash

while [ -n "$1" ]; do
    case "$1" in
    -a)
        echo "found -a option"
        ;;
    -b)
        echo "found -b option"
        ;;
    -c)
        echo "found -c option"
        ;;
    *)
        echo "$1 is not define"
        ;;
    esac
    shift
done

Varfile¶

#!/bin/bash

x=10
echo :$x:

Color¶

#!/bin/bash

WHITE='\033[0;47m'
BOLD_WHITE='\033[1;47m'
BLACK='\033[0;30m'
BOLD_BLACK='\033[1;30m'
BLUE='\033[0;34m'
BOLD_BLUE='\033[1;34m'
RED='\033[0;31m'
BOLD_RED='\033[1;31m'
GREEN='\033[0;32m'
BOLD_GREEN='\33[1;32m'
YELLOW='\033[0;33m'
BOLD_YELLOW='\033[1;33m'
PURPLE='\033[0;35m'
BOLD_PURPLE='\033[1;35m'
NC='\033[0m' # No Color

### effects
#  echo -e "\033[0;33mSample text"
#  echo -e "\033[1;37mBold text"
#  echo -e "\033[2;33mLow intensity text"
#  echo -e "\033[4;33mUnderline text"
#  echo -e "\033[5;33mBlinking text"
#  echo -e "\033[8;33mInvisible text"
#  echo -e "\033[9;33mStrikethrough text${NC}"

#echo -e "${BLUE}blue ${RED}red${NC} ${YELLOW}yellow "
printf "${BLUE}blue ${RED}red ${GREEN}green ${WHITE}white ${BLACK}black ${YELLOW}yellow ${PURPLE}purple ${NC}\n"
printf "${BOLD_BLUE}bold_blue ${BOLD_RED}bold_red ${BOLD_GREEN}bold_green ${BOLD_WHITE}bold_white ${NC} ${BOLD_BLACK}bold_black ${BOLD_YELLOW}bold_yellow ${BOLD_PURPLE}bold_purple ${NC}\n"

Code¶

Decision Making¶

IF¶

Check File Type¶

Check Input Arguments¶

Is Integer?¶

Is String?¶

Switch Case¶

By Predefined Arguments¶

Select¶

Loop Condition¶

For¶

While¶

Break¶

Continue¶

$¶

Input Parameters¶

Difference of $@ & $#¶

Exec¶

exec-in¶

exec-out¶

Check Exist Username¶

Basic Input¶

Close File Descriptor¶

Add Integers¶

Get Current working directory and Basename¶

Directory Basename¶

Print current directory¶

Print basename¶

Factorial¶

Function¶

lsof¶

Memory Alert¶

Parameters Options¶

Read From File¶

Redirection Priority¶

Shift Over Option¶

Varfile¶

Color¶

Difference of `$@` & `$#`¶