Bash examples
Source https://linuxhint.com/30_bash_script_examples/
First BASH Program
You can run bash script from the terminal or by executing any bash file. Run the following command from the terminal to execute a very simple bash statement. The output of the command will be ‘Hello World’.
$ echo "Hello World"
Open any editor to create a bash file. Here, nano editor is used to create the file and filename is set as ‘First.sh’.
$ nano First.sh
Add the following bash script to the file and save the file.
#!/bin/bash
echo "Hello World"
You can run bash file by two ways. One way is by using bash command and another is by setting execute permission to bash file and run the file. Both ways are shown here.
$ bash First.sh
Or,
$ chmod a+x First.sh
$ ./First.sh
echo command
You can use echo command with various options. Some useful options are mentioned in the following example.
When you use ‘echo’ command without any option then a newline is added by default. ‘-n’ option
is used to print any text without new line and ‘-e’ option is used to remove backslash characters
from the output. Create a new bash file with a name, ‘echo_example.sh’ and add the following script.
#!/bin/bash
echo "Printing text with newline"
echo -n "Printing text without newline"
echo -e "\nRemoving \t backslash \t characters\n"
comment
‘#’ symbol is used to add single line comment in bash script. Create a new file named ‘comment_example.sh’ and add
the following script with single line comment.
#!/bin/bash
# Add two numeric value
((sum=25+35))
#Print the result
echo $sum
Multi-line comment
You can use multi line comment in bash in various ways. A simple way is shown in the following example. Create a new bash named,
‘multiline-comment.sh’ and add the following script. Here, ‘:’ and “ ’ ” symbols are used to add multiline
comment in bash script. This following script will calculate the square of 5.
#!/bin/bash
: '
The following script calculates
the square value of the number, 5.
'
((area=5*5))
echo $area
You can check the following link to know more about the use of bash comment.
https://linuxhint.com/bash_comments/
While Loop
Create a bash file with the name, ‘while_example.sh’, to know the use of while loop. In the example, while loop will iterate for 5 times. The value of count variable will increment by 1 in each step. When the value of count variable will 5 then the while loop will terminate.
#!/bin/bash
valid=true
count=1
while [ $valid ]
do
echo $count
if [ $count -eq 5 ];
then
break
fi
((count++))
done
You can check the following link to know more about the use of while loop.
https://linuxhint.com/bash-while-loop-examples/
For Loop
The basic for loop declaration is shown in the following example. Create a file named ‘for_example.sh’ and add the
following script using for loop. Here, for loop will iterate for 10 times and print all values of the variable,
counter in single line.
#!/bin/bash
for (( counter=10; counter>0; counter-- ))
do
echo -n "$counter "
done
printf "\n"
You can use for loop for different purposes and ways in your bash script. You can check the following link to know more about the use of for loop.
https://linuxhint.com/bash-for-loop-examples/
User Input
‘read’ command is used to take input from user in bash. Create a file named ‘user_input.sh’ and add the following
script for taking input from the user. Here, one string value will be taken from the user and display the value
by combining other string value.
#!/bin/bash
echo "Enter Your Name"
read name
echo "Welcome $name to LinuxHint"
You can check the following link to know more about the use of user input.
https://linuxhint.com/bash-script-user-input/
if statement
You can use if condition with single or multiple conditions. Starting and ending block of this statement is
define by ‘if’ and ‘fi’. Create a file named ‘simple_if.sh’ with the following script to know the use if statement
in bash. Here, 10 is assigned to the variable, n. if the value of $n is less than 10 then the output will be
“It is a one digit number”, otherwise the output will be “It is a two digit number”. For comparison, ‘-lt’ is used
here. For comparison, you can also use ‘-eq’ for equality, ‘-ne’ for not equality and ‘-gt’ for greater than in
bash script.
#!/bin/bash
n=10
if [ $n -lt 10 ];
then
echo "It is a one digit number"
else
echo "It is a two digit number"
fi
if statement with AND logic
Different types of logical conditions can be used in if statement with two or more conditions. How you can define multiple conditions in
if statement using AND logic is shown in the following example. ‘&&’ is used to apply AND logic of if statement.
Create a file named ‘if_with_AND.sh’ to check the following code. Here, the value of username and password variables will be taken
from the user and compared with ‘admin’ and ‘secret’. If both values match then the output will be “valid user”,
otherwise the output will be “invalid user”.
!/bin/bash
echo "Enter username"
read username
echo "Enter password"
read password
if [[ ( $username == "admin" && $password == "secret" ) ]]; then
echo "valid user"
else
echo "invalid user"
fi
if statement with OR logic
‘||’ is used to define OR logic in if condition. Create a file named ‘if_with_OR.sh’ with the following code to check the use
of OR logic of if statement. Here, the value of n will be taken from the user. If the value is equal to 15 or 45 then the
output will be “You won the game”, otherwise the output will be “You lost the game”.
#!/bin/bash
echo "Enter any number"
read n
if [[ ( $n -eq 15 || $n -eq 45 ) ]]
then
echo "You won the game"
else
echo "You lost the game"
fi
else if statement
The use of else if condition is little different in bash than other programming language. ‘elif’ is used to define else if
condition in bash. Create a file named, ‘elseif_example.sh’ and add the following script to check how else if is defined in bash script.
#!/bin/bash
echo "Enter your lucky number"
read n
if [ $n -eq 101 ];
then
echo "You got 1st prize"
elif [ $n -eq 510 ];
then
echo "You got 2nd prize"
elif [ $n -eq 999 ];
then
echo "You got 3rd prize"
else
echo "Sorry, try for the next time"
fi
Case Statement
Case statement is used as the alternative of if-elseif-else statement. The starting and ending block of this
statement is defined by ‘case’ and ‘esac’. Create a new file named, ‘case_example.sh’ and add the following
script. The output of the following script will be same to the previous else if example.
#!/bin/bash
echo "Enter your lucky number"
read n
case $n in
101)
echo echo "You got 1st prize" ;;
510)
echo "You got 2nd prize" ;;
999)
echo "You got 3rd prize" ;;
*)
echo "Sorry, try for the next time" ;;
esac
Arguments from Command Line
Bash script can read input from command line argument like other programming language. For example,
$1 and $2 variable are used to read first and second command line arguments. Create a file named
“command_line.sh” and add the following script. Two argument values read by the following script and
prints the total number of arguments and the argument values as output.
#!/bin/bash
echo "Total arguments : $#"
echo "1st Argument = $1"
echo "2nd argument = $2"
You can check the following link to know more about the use of command line argument.
https://linuxhint.com/command_line_arguments_bash_script/
arguments from command line with names
How you can read command line arguments with names is shown in the following script. Create a file named,
‘command_line_names.sh’ and add the following code. Here, two arguments, X and Y are read by this script and print the sum of X and Y.
#!/bin/bash
for arg in "$@"
do
index=$(echo $arg | cut -f1 -d=)
val=$(echo $arg | cut -f2 -d=)
case $index in
X) x=$val;;
Y) y=$val;;
*)
esac
done
((result=x+y))
echo "X+Y=$result"
Run the file with bash command and with two command line arguments.
$ bash command_line_names X=45 Y=30
Combine String variables
You can easily combine string variables in bash. Create a file named “string_combine.sh” and add the following script
to check how you can combine string variables in bash by placing variables together or using ‘+’ operator.
#!/bin/bash
string1="Linux"
string2="Hint"
echo "$string1$string2"
string3=$string1+$string2
string3+=" is a good tutorial blog site"
echo $string3
Get substring of String
Like other programming language, bash has no built-in function to cut value from any string data. But you can do the task
of substring in another way in bash that is shown in the following script. To test the script, create a file named
‘substring_example.sh’ with the following code. Here, the value, 6 indicates the starting point from where the
substring will start and 5 indicates the length of the substring.
#!/bin/bash
Str="Learn Linux from LinuxHint"
subStr=${Str:6:5}
echo $subStr
Add Two Numbers
You can do the arithmetical operations in bash in different ways. How you can add two integer numbers in bash using double
brackets is shown in the following script. Create a file named ‘add_numbers.sh’ with the following code. Two integer
values will be taken from the user and printed the result of addition.
#!/bin/bash
echo "Enter first number"
read x
echo "Enter second number"
read y
(( sum=x+y ))
echo "The result of addition=$sum"
You can check the following link to know more about bash arithmetic.
https://linuxhint.com/bash_arithmetic_operations/
Create Function:
How you can create a simple function and call the function is shown in the following script. Create a file named
‘function_example.sh’ and add the following code. You can call any function by name only without using any
bracket in bash script.
#!/bin/bash
function F1()
{
echo 'I like bash programming'
}
F1
Create function with Parameters
Bash can’t declare function parameter or arguments at the time of function declaration. But you can use parameters
in function by using other variable. If two values are passed at the time of function calling then $1 and $2
variable are used for reading the values. Create a file named ‘function|_parameter.sh’ and add the following
code. Here, the function, ‘Rectangle_Area’ will calculate the area of a rectangle based on the parameter values.
#!/bin/bash
Rectangle_Area() {
area=$(($1 * $2))
echo "Area is : $area"
}
Rectangle_Area 10 20
Pass Return Value from Function
Bash function can pass both numeric and string values. How you can pass a string value from the function is shown in the
following example. Create a file named, ‘function_return.sh’ and add the following code. The function, greeting()
returns a string value into the variable, val which prints later by combining with other string.
#!/bin/bash
function greeting() {
str="Hello, $name"
echo $str
}
echo "Enter your name"
read name
val=$(greeting)
echo "Return value of the function is $val"
You can check the following link to know more about the use of bash function.
https://linuxhint.com/return-string-bash-functions/
Make Directory
Bash uses ‘mkdir’ command to create a new directory. Create a file named ‘make_directory.sh’ and add the following
code to take a new directory name from the user. If the directory name is not exist in the current location then it will
create the directory, otherwise the program will display error.
#!/bin/bash
echo "Enter directory name"
read newdir
`mkdir $newdir`
Make directory by checking existence
If you want to check the existence of directory in the current location before executing the ‘mkdir’ command then you can
use the following code. ‘-d’ option is used to test a particular directory is exist or not. Create a file named,
‘directory_exist.sh’ and add the following code to create a directory by checking existence.
#!/bin/bash
echo "Enter directory name"
read ndir
if [ -d "$ndir" ]
then
echo "Directory exist"
else
`mkdir $ndir`
echo "Directory created"
fi
You can check the following link to know more about directory creation.
https://linuxhint.com/bash_mkdir_not_existent_path/
Read a File
You can read any file line by line in bash by using loop. Create a file named, ‘read_file.sh’ and
add the following code to read an existing file named, ‘book.txt’.
#!/bin/bash
file='book.txt'
while read line; do
echo $line
done < $file
You can check the following link to know the different ways to read file.
https://linuxhint.com/read_file_line_by_line_bash/
Delete a File
‘rm’ command is used in bash to remove any file. Create a file named ‘delete_file.sh’ with the following
code to take the filename from the user and remove. Here, ‘-i’ option is used to get permission from the
user before removing the file.
#!/bin/bash
echo "Enter filename to remove"
read fn
rm -i $fn
Append to File
New data can be added into any existing file by using ‘>>’ operator in bash. Create a file named ‘append_file.sh’
and add the following code to add new content at the end of the file. Here, ‘Learning Laravel 5’ will
be added at the of ‘book.txt’ file after executing the script.
#!/bin/bash
echo "Before appending the file"
cat book.txt
echo "Learning Laravel 5">> book.txt
echo "After appending the file"
cat book.txt
Test if File Exist
You can check the existence of file in bash by using ‘-e’ or ‘-f’ option. ‘-f’ option is used in the
following script to test the file existence. Create a file named, ‘file_exist.sh’ and add the following code.
Here, the filename will pass from the command line.
#!/bin/bash
filename=$1
if [ -f "$filename" ]; then
echo "File exists"
else
echo "File does not exist"
fi
Run the following commands to check the existence of the file. Here, book.txt file exists and book2.txt is not exist in the current location.
$ ls
$ bash file_exist.sh book.txt
$ bash file_exist.sh book2.txt
Send Email
You can send email by using ‘mail’ or ‘sendmail’ command. Before using these commands, you have to install all
necessary packages. Create a file named, ‘mail_example.sh’ and add the following code to send the email.
#!/bin/bash
Recipient=”admin@example.com”
Subject=”Greeting”
Message=”Welcome to our site”
`mail -s $Subject $Recipient <<< $Message`
Parse Current Date
You can get the current system date and time value using date command. Every part of date and time value can be parsed
using ‘Y’, ‘m’, ‘d’, ‘H’, ‘M’ and ‘S’. Create a new file named ‘date_parse.sh’ and add
the following code to separate day, month, year, hour, minute and second values.
#!/bin/bash
Year=`date +%Y`
Month=`date +%m`
Day=`date +%d`
Hour=`date +%H`
Minute=`date +%M`
Second=`date +%S`
echo `date`
echo "Current Date is: $Day-$Month-$Year"
echo "Current Time is: $Hour:$Minute:$Second"
Wait Command
wait is a built-in command of Linux that waits for completing any running process. wait command is used with a
particular process id or job id. If no process id or job id is given with wait command then it will wait for all current
child processes to complete and returns exit status. Create a file named ‘wait_example.sh’ and add the following script.
#!/bin/bash
echo "Wait command" &
process_id=$!
wait $process_id
echo "Exited with status $?"
See more https://linuxhint.com/wait_command_linux/
Sleep Command
When you want to pause the execution of any command for specific period of time then you can use sleep command.
You can set the delay amount by seconds (s), minutes (m), hours (h) and days (d). Create a file
named ‘sleep_example.sh’ and add the following script. This script will wait for 5 seconds after running.
#!/bin/bash
echo “Wait for 5 seconds”
sleep 5
echo “Completed”
You can check the following link to know more about sleep command.