Linux CLI Basics

9 examples to get you started with Linux CLI - 6 basic and 3 intermediate.

Prerequisites

• A bash or zsh shell on Linux, macOS, or WSL (these commands are the same across all three).
• The AWS CLI v2 installed, since several examples pipe its output.
• No special setup beyond a terminal - every command here ships with the OS.

Basic Examples

1. Move Around and Orient Yourself

pwd, cd, and ls are the three commands you use before anything else.

pwd                     # print the current directory
cd ~/projects/my-sdk-app
ls -la                  # list all files, including hidden ones, with details

• ls -la reveals hidden files like .env and .aws, which do not show with a plain ls.
• cd - jumps back to the previous directory, handy when bouncing between two folders.
• pwd is worth running before any command that deletes or overwrites files, so you know exactly where you are.

2. Read Files Without Opening an Editor

cat, head, and tail print file contents straight to the terminal.

cat requirements.txt          # print the whole file
head -n 20 app.log            # first 20 lines
tail -n 20 app.log            # last 20 lines
tail -f app.log                # follow new lines as they are written

• tail -f is the standard way to watch a log file while an SDK script is running.
• head is useful for checking a large describe-* JSON dump without scrolling forever.
• Both accept -c to count bytes instead of lines, rarely needed but good to know exists.

3. Search Text With grep

grep finds lines matching a pattern, across one file or a whole tree.

grep "AccessDenied" app.log
grep -r "boto3.client" .          # recursive search from the current directory
grep -i "error" app.log            # case-insensitive
grep -n "region_name" config.py    # show line numbers

• -r is what you reach for when you cannot remember which file defines something.
• -i avoids missing matches because of casing (Error vs error).
• Combine with pipes: aws ... | grep InstanceId filters CLI output the same way.

Related: jq & Parsing AWS CLI/SDK JSON Output - a more precise way to filter structured JSON than grep.

4. Find Files by Name or Type

find locates files across a directory tree by name, extension, or modification time.

find . -name "*.py"                 # every Python file under the current dir
find . -name "*.tf" -newer main.tf   # Terraform files edited after main.tf
find . -type d -name "__pycache__"  # locate directories to clean up

• find searches the filesystem tree; grep -r searches file contents. Use find when you know the name, grep -r when you know the content.
• Pair with -exec to act on results, e.g. find . -name "*.pyc" -exec rm {} \;.
• Always scope find to a project directory, not /, to avoid scanning the entire disk.

5. Chain Commands With Pipes and Redirection

A pipe (|) sends one command's output into the next; > and >> write output to a file.

aws ec2 describe-instances --output json > instances.json   # save to a file
cat instances.json | grep "InstanceId"                      # then search it
aws s3 ls | grep "my-bucket"                                  # or filter directly
echo "run started" >> deploy.log                              # append a line

• > overwrites a file; >> appends. Mixing them up is a common way to lose a log's history.
• Piping the CLI's json output into jq (next page) is far more precise than piping into grep.
• 2>&1 redirects stderr into the same stream as stdout, useful when capturing a full command's output including errors.

6. Set and Inspect Environment Variables

export sets a variable for the current shell session; echo $VAR reads one back.

export AWS_PROFILE=dev
export AWS_REGION=us-east-1
echo $AWS_PROFILE
unset AWS_PROFILE           # remove it when you are done with that scope

• export makes the variable visible to any program you launch from this shell, including aws, python, and node.
• Without export, a plain assignment (AWS_PROFILE=dev) is only visible to the current shell, not to programs it launches.
• Always unset a scoped credential-related variable when you finish a task - covered in depth on the env vars and credentials page.

Intermediate Examples

7. Manage File Permissions on Credential Files

chmod and ls -l control and reveal who can read a file - critical for ~/.aws/credentials.

ls -l ~/.aws/credentials
# -rw------- 1 you you 123 Jul 23 10:00 /Users/you/.aws/credentials
 
chmod 600 ~/.aws/credentials   # owner read/write only, nobody else

• 600 means only the file owner can read or write it - no group or world access.
• The AWS CLI does not enforce this permission for you; a shared or misconfigured machine can leave the file world-readable.
• Run this check once after any manual edit to ~/.aws/credentials or ~/.aws/config.

8. Combine Commands With && and ;

&& runs the next command only if the previous one succeeded; ; runs it regardless.

aws sts get-caller-identity && echo "credentials OK"
mkdir -p build && cd build && python ../deploy.py
false ; echo "this still runs"

• && is the safer default for scripts, since a failed step stops the chain instead of continuing on bad state.
• $? holds the exit code of the last command if you need to check it explicitly: echo $?.
• Use set -euo pipefail at the top of a bash script to make every step behave like it is chained with &&.

9. Background and Manage Long-Running Processes

&, jobs, and kill let you run something in the background and control it later.

python long_poll.py &      # run in the background, prompt returns immediately
jobs                        # list background jobs in this shell
kill %1                     # stop job 1

• nohup command & keeps a background process alive after you close the terminal.
• Ctrl+Z suspends the current foreground job; bg resumes it in the background, fg brings it back.
• For anything you need to survive a logout reliably, prefer a real process manager or a scheduled job over an ad hoc background shell.

Related

• The Shell as an AWS SDK Developer's Companion - why these commands matter alongside SDK code.
• jq & Parsing AWS CLI/SDK JSON Output - filtering AWS JSON precisely instead of with grep.
• Managing AWS Env Vars & Credentials Safely in Shell Sessions - handling export/unset for secrets correctly.
• Linux CLI Best Practices - habits to build on top of these basics.

Stack versions: This page was written for boto3 1.43.x (Python 3.10+) and the AWS SDK for JavaScript v3 (Node.js 18+).