Shell scripting is a powerful method to automate tasks and manage system operations in Linux. A shell script is essentially a text file containing a series of commands interpreted by the shell, such as Bash. By writing shell scripts, users can automate repetitive processes, simplify complex tasks, and improve productivity.
What is a Shell Script?
A shell script is a file containing a sequence of shell commands. It allows execution of multiple commands as a single program. Shell scripts are interpreted, not compiled, meaning each command runs line-by-line. It typically started with a shebang line (#!/bin/bash) indicating the script interpreter.
Creating Your First Shell Script
The following are the basic steps to create and run a simple shell script. They introduce how scripts are written, saved, and executed in Linux.
1. Open a text editor and write the script, for example:
#!/bin/bash
echo "Hello, World!"2. Save the file with .sh extension, e.g., hello.sh.
3. Make the script executable:
chmod +x hello.sh4. Run the script:
./hello.shThe output will be:
Hello, World!Basic Components of Shell Scripts
Below are the essential parts that allow a shell script to work effectively. They help manage data, commands, and user interaction.
1. Comments: Begin with #, used to document the script.
2. Commands: Regular Linux shell commands.
3. Variables: Store data for reuse.
Example:
NAME="Alice"
echo "Hello, $NAME"4. User Input: Read input with read.
Example:
echo "Enter your name:"
read USERNAME
echo "Welcome, $USERNAME"Control Structures
The following are the key control structures used in shell scripting. They decide how and when commands are executed.
1. Conditional Statements: Execute commands based on conditions.
Example:
if [ $AGE -ge 18 ]; then
echo "Adult"
else
echo "Minor"
fi2. Loops: Repeat commands.
for loop example:
for i in 1 2 3
do
echo "Number $i"
donewhile loop example:
count=1
while [ $count -le 5 ]
do
echo "Count: $count"
((count++))
doneBasic Shell Commands Useful in Scripts
Running Shell Scripts
Below are the common techniques for running shell scripts. They allow scripts to receive arguments and behave dynamically.
1. Run scripts by specifying the path:
./script.sh2. Or specify interpreter explicitly:
bash script.sh3. Pass arguments to scripts and access them via $1, $2, etc.
Example:
echo "Argument 1 is $1"Run with:
./script.sh HelloOutput:
Argument 1 is Hello