Shell scripting fundamentals (variables, loops, conditionals) – Linux Shell and Shell Scripting – Linux operating system

Shell scripting is a powerful feature of Linux shells that allows you to automate tasks and create scripts to execute a series of commands. Here are some fundamental concepts of shell scripting:

1. Variables:
   • Variables in shell scripts are used to store and manipulate data.
   • Variable names are case-sensitive and typically uppercase by convention.
   • To assign a value to a variable, use the syntax variable_name=value.
   • Example: name="John"
2. Command Substitution:
   • Command substitution allows you to capture the output of a command and assign it to a variable.
   • Use the syntax variable_name=$(command) or `command` to assign the output of the command to the variable.
   • Example: files=$(ls)
3. Conditionals:
   • Conditionals are used to make decisions based on certain conditions.
   • Common conditional constructs in shell scripting include if, elif, and else.
   • Example:bashCopyif [ condition ]; then # code to execute if the condition is true elif [ condition ]; then # code to execute if the previous condition is false and this condition is true else # code to execute if all previous conditions are false fi
4. Comparison Operators:
   • Comparison operators are used in conditionals to compare values.
   • Common comparison operators include -eq (equal), -ne (not equal), -lt (less than), -gt (greater than), -le (less than or equal), and -ge (greater than or equal).
   • Example: [ $num -gt 10 ]
5. String Comparison:
   • To compare strings, you can use operators such as = (equal), != (not equal), < (less than), and > (greater than).
   • Example: [ "$name" = "John" ]
6. Loops:
   • Loops allow you to repeat a block of code until a specific condition is met.
   • Common loop constructs in shell scripting include for and while.
   • Example: for variable in list; do # code to execute for each item in the list done while [ condition ]; do # code to execute while the condition is true done
7. Command Line Arguments:
   • Shell scripts can accept command line arguments passed when executing the script.
   • Arguments are accessed using special variables like $1, $2, etc., where $1 represents the first argument, $2 represents the second argument, and so on.
   • Example: script.sh arg1 arg2

These are some fundamental concepts of shell scripting in Linux. By using variables, conditionals, and loops, you can create powerful scripts to automate tasks and perform complex operations. Shell scripting is versatile and can be used for a wide range of tasks, from simple automation to more intricate system administration tasks.