How to Write a Simple Bash Script on Linux

What Is a Bash Script?

A Bash script is a text file containing shell commands that are executed in sequence. Scripts let you automate repetitive tasks, set up servers, process files, and anything else you'd do manually in the terminal.

Step 1 — Create the Script File

nano ~/scripts/hello.sh

Step 2 — Add the Shebang Line

The first line of every Bash script tells the OS which interpreter to use:

#!/bin/bash

This is called the shebang. Always include it.

Step 3 — Variables

Variables are set without spaces around = and referenced with $:

#!/bin/bash
NAME="Alice"
TODAY=$(date +%Y-%m-%d)        # command substitution

echo "Hello, $NAME!"
echo "Today is $TODAY"

Step 4 — User Input

#!/bin/bash
echo "What is your name?"
read NAME
echo "Hello, $NAME!"

Step 5 — Conditionals

#!/bin/bash
FILE="/etc/passwd"

if [ -f "$FILE" ]; then
  echo "$FILE exists"
else
  echo "$FILE not found"
fi

Common test operators: -f (file exists), -d (directory), -z (empty string), -eq (equal numbers), -gt (greater than).

Step 6 — Loops

# Loop over a list
for FRUIT in apple banana cherry; do
  echo "I like $FRUIT"
done

# Loop over files
for FILE in ~/Documents/*.txt; do
  echo "Processing: $FILE"
done

# While loop
COUNT=1
while [ $COUNT -le 5 ]; do
  echo "Count: $COUNT"
  ((COUNT++))
done

Step 7 — Make It Executable and Run It

chmod +x ~/scripts/hello.sh     # make executable
~/scripts/hello.sh               # run it

Or run it explicitly with bash: bash ~/scripts/hello.sh

A Practical Example: Backup Script

#!/bin/bash

SOURCE="$HOME/Documents"
DEST="$HOME/backups"
DATE=$(date +%Y-%m-%d)

mkdir -p "$DEST"
tar -czf "$DEST/docs-$DATE.tar.gz" "$SOURCE"
echo "Backup created: $DEST/docs-$DATE.tar.gz"

Script Best Practices

• Always start with #!/bin/bash
• Add set -e at the top to stop on any error
• Quote variables: "$VAR" not $VAR — prevents word-splitting bugs
• Test your script on sample data before running on production