lets bash scripting

Estimated reading time: 6 minutes

bash

bash = Bourne-Again SHell

comments

# this is single line comment
echo "kamal is a code artist" # this is comment
# output: kamal is a code artist

variable

local variable

name="kamal"
echo $name
# output: kamal
  • local keyword uses inside function
name="kamal"
user(){
  local name="jamal"
  echo $name
}
echo $name
#output:
# jamal
# kamal

global variable

export price=51

default varibale

name="jamal"
echo ${name:="kamal"}
# jamal

echo ${name:="kamal"}
# kamal

read

read -p "submit your name: " name
echo $name

string

status="Mostafa Kamal   is    a     code artist"
echo $status
# Mostafa Kamal is a code artist
echo "$status"
# Mostafa Kamal   is    a     code artist

name="kamal"
echo 'this is $name'
# thi is $name
echo "this is $name"
# this is kamal

arithmatic

  • $(( .. ))
x=5
y=7
echo (( x + y ))
# 12

array

users=("kamal" "jamal" "maruf" "sadia")
echo ${users[1]}
# output: jamal
users=("kamal" "jamal" "maruf" "sadia")
echo ${users[@]} # [@] or [*] retrive all
# output: kamal jamal maruf sadia
users=("kamal" "jamal" "maruf" "sadia")
echo ${#users[@]}
# output : 4
# retrive array size

array add

users=("kamal" "jamal" "maruf" "sadia")
employee=("kamrul" "${users[@]}" "faruk")
echo ${employee[@]}
# output: kamrul kamal jamal maruf sadia faruk

array slice

users=("kamal" "jamal" "maruf" "sadia")
echo ${users[@]:1:2}
# output: jamal maruf

delete array ele

users=("kamal" "jamal" "maruf" "sadia")
unset users[1]
echo ${users[@]}
# output: kamal maruf sadia

operator

arithmatic operator description
-eq equal
-ne not equal
-lt less than
-le less than or equal
-gt greater than
-ge greater than or equal

condition

  • single square bracket [condition] or double square bracket [[condtion]]
  • ubuntu system basicaly not support [[ not support ]]
    • access [[ double]] command sudo bash myfile.sh
    • On Ubuntu systems, /bin/sh is dash, not bash, and dash does not support the double bracket

if

if [ 2 -eq 2 ]; then
  echo "the number is 2"
fi
# output : the number is 2

if-else

number=2
if [ $number -eq 3 ]; then
  echo "the number is 2"
else
  echo "the number is not 2"
fi
# output : the number is 2

elseif

number=2
if [ $number -eq 3 ]; then
  echo "the number is 3"
elif [ $number -eq 2 ]; then
  echo "the number is 2"
else
  echo "the number is not 2"
fi
# output : the number is 2

case

number=5
case $number in
  2 )
    echo "the number is 2"
  ;;
  3 )
    echo "the number is 3"
  ;;
  * )
    echo "not 2 or 3"
  ;;
esac
# output: not 2 or 3

loop

for

users=("kamal" "jamal" "sadia" "maruf")
for i in ${users[@]}; do
  echo $i
done
# kamal jamal sadia maruf

for (( i=0; i < 10 ; i++)); do
  echo $i
done
# 0 1 2 3 4 5 6 7 8 9

continue

for (( i=0; i < 10; i++)); do
  if [ $(( i % 2 )) -eq 0]; then
    continue
  fi
  echo $i
done
# 1 3 5 7 9

break

for (( i=0; i < 10; i++)); do
  if [ $i -eq 5]; then
    break
  fi
  echo $i
done
# 0 1 2 3 4

while

i=0
while [ $i -lt 10 ]; do
  echo $i
  i=$(( i + 1 ))
done
# 0 1 2 3 4 5 6 7 8 9

until

  • until is opposite of while
i=0
until [ $i -gt 10 ]; do
  echo $i
  i=$(( i + 1 ))
done
# 0 1 2 3 4 5 6 7 8 9

command

multiple command

uname
id -u
whoami

and comannd

# uname && id -u

or comannd

# unamed || id -u
# unamed is wrong command
# uname is actual command

function

read name
create(){
  adduser $1
}
create $name
linux, shell, bash, sh