Introduction to Shell Scripting: Variables, Strings, Conditionals, Loops, and Execution

Shell scripting is presented as a practical way to build small automation tools such as hardware checks, one‑click web environment setup, and log analysis, making it ideal for beginners who want to write useful scripts.

Creating a shell script : Use vi test.sh to create a file, and start it with the shebang line #!/bin/bash.

Shell variables : Define a variable with a=10, print it with echo $a or echo ${a}. Read‑only variables are created with readonly your_name, and variables can be removed with unset a (note that unset cannot delete read‑only variables).

String literals : Single quotes preserve the exact characters ( str='this is a apple') and do not expand variables, while double quotes allow variable expansion ( str="this is a apple2") and support escape sequences.

Echo command : echo "\"it is a bug\"" prints "it is a bug". Use \n for a newline and \c to suppress the trailing newline.

If‑else statements :

#!/bin/bash
 a=10
 b=20
 if [ $a == $b ]
 then
   echo "a is equal to b"
 fi
 if [ $a != $b ]
 then
   echo "a is not equal to b"
 fi

The script outputs a is not equal to b. Additional forms such as if..else..fi and if..elif..fi follow the same structure.

For loop example:

for loop in 1 2 2 3
do
  echo "$loop"
done

The loop syntax is for … in …; do …; done.

While loop example:

int=1
while(($int<=5))
do
  echo $int
  let "int++"
done

Demonstrates a numeric condition and increment.

Executing a shell script : Either grant execute permission and run chmod +x ./hello.sh && ./hello.sh, or invoke the interpreter directly with bash hello.sh or sh hello.sh.

The article concludes with a practice exercise to write a script that calculates the factorial of 10 using the commands introduced.