Combining Commands

Beyond pipes, Linux provides several ways to combine and control command execution.

Command Separators

Operator	Meaning	Example
;	Run sequentially	cmd1 ; cmd2
&&	Run if previous succeeds	cmd1 && cmd2
`		`
&	Run in background	cmd &

Sequential Execution: ;

Run commands one after another:

echo "Starting" ; date ; echo "Done"

The second command runs regardless of whether the first succeeds.

Conditional AND: &&

Run second command only if first succeeds:

mkdir newdir && cd newdir

If mkdir fails, cd won't run (preventing errors).

Conditional OR: ||

Run second command only if first fails:

cd /nonexistent || echo "Directory not found"

Exercise: Use Conditional Execution

Create a directory and show a success message:

Combining && and ||

Create success/failure handlers:

command && echo "Success" || echo "Failed"

Background Execution: &

Run a command in the background:

long_running_command &

The shell returns immediately while the command runs.

Common Patterns

Safe Directory Creation

mkdir -p dir && cd dir

Compile and Run

gcc program.c -o program && ./program

Test and Deploy

npm test && npm run build && npm run deploy

Default Values

cd "$DIR" || cd /tmp

Create If Not Exists

[ -d "backup" ] || mkdir backup

Grouping Commands

Subshell: ()

Commands run in a subshell:

(cd /tmp && ls)    # Changes dir only in subshell
pwd                 # Still in original directory

Current Shell:

Commands run in current shell:

{ cd /tmp && ls; }
pwd                 # Now in /tmp

Practical Examples

Backup and Verify

cp file.txt backup/ && ls backup/file.txt && echo "Backup complete"

Update System

apt update && apt upgrade -y

Install Dependencies

npm install || yarn install || echo "Install failed"

Exercise: Chain Commands

Run multiple commands that depend on each other:

Summary Table

Pattern	Use Case
cmd1 ; cmd2	Always run both
cmd1 && cmd2	Run cmd2 if cmd1 succeeds
`cmd1
cmd &	Run in background
(cmd1; cmd2)	Run in subshell

Key Takeaways

• ; runs commands sequentially regardless of success
• && runs next command only if previous succeeds
• || runs next command only if previous fails
• Combine && and || for success/failure handling
• Use & to run commands in the background