Linux commands crash course

Command Line hands-on

Usage

• Clear history: `ctrl + l`
• Clear everything left from current cursor position: `ctrl + u`
• Clear everything right from current cursor position: `ctrl + k`
• Re-call last input with sudo: `sudo !!`
• Stop current process: `ctrl + c`
• Jump to left: `ctrl + a`
• Jump to right: `ctrl + e`
• Help: `help cd` / `help dir` (…)
• Finding Help: `apropos directory` / `apropos search` (…)
• Define custom startup screen: `sudo nano /etc/motd`
• Run a script as a background process: `python script.py &`
• List all running process’s: `ps aux`
• Kill a running process: `sudo kill 12345`

System

• Get the current path: `pwd`
• Copy to clipboard: `pwd | pbcopy`
• Paste: `pbpaste`
• Get the current hostname: `hostname`
• Get the current users: `users`
• Get all info about the environment: `env`
• Show calendar: `cal`
• Show today’s date: `date`
• Exit terminal: `exit`

Directories

List directory contents: ls

List all directory contents: ll

List all directory contents sorted by time edited: ls -alt

List directory (wildcard matching): ls *.txt

List all files of type: find . -name "*.txt" -print

Go back to the previous directory: cd — or cd ..

Make (empty) directory: mkdir sample-dirname

Remove (empty) directory: rmdir sample-dirname

Remove the directory with all contents: rm -rf sample-dirname/

Remove directory contents and keep directory: rm -rf *

Checkout directory: cd sample-dirname

Browsing directories: pushd sample-dirname / popd / dirs (see http://unix.stackexchange.com/a/77081)

Permissions

• Use the `-R` option to change permissions recursively.
• List: `ps -ef | grep apache | grep -v grep`
• Change permissions: `chmod 755 index.php`
• Change owner: `chown root index.php` (`root` is the username)
• Change group: `chgrp www-data index.php` (`www-data` is the groupname)

WordPress Files/Folder Permissions

Let apache be owner: chown www-data:www-data -R *

Change directory permissions rwxr-xr-x: find . -type d -exec chmod 755 {} \;

Change file permissions rw-r — r — : find . -type f -exec chmod 644 {} \;

(see http://stackoverflow.com/a/18352747/1815847)\

Symlinks

Create symlink: ln -s source-dirname destination-dirname

Update symlink: ln -sfn source-dirname destination-dirname

Remove symlink: unlink sample-dirname

• -s: Create a symbolic link.
• -f: If the target file already exists, then unlink it.
• -F: If the target file already exists and is a directory, then remove/overwrite it.
• -h: If the target file or directory is a symbolic link, do not follow it.
• -n: Same as -h, for compatibility with other ln implementations.

Files

Make (empty) file: touch sample-filename.txt

Change creation date: touch –t 201401011337 sample-filename.txt

Change modified date: touch –mt 201401011337 sample-filename.txt

Duplicate file: cp sample-filename.txt sample-filename-copy.txt

Copy/Page folder with content: cp -a folder/ new_folder

Move/Rename file: mv current-filename.txt new-filename.txt

Move/Rename the file and prompt before overwriting an existing file: mv -i current-filename.txt new-filename.txt

Remove file: rm sample-filename.txt

View file: less sample-filename.txt / more sample-filename.txt

Write to file (will overwrite existing content): cat > sample-filename.txt (quit with ctrl+d)

Search for a filename (not content!) in the current directory: find sample-filename.txt

Search for a string (not filename!) inside all files in the current directory: ack "string" --php (documentation)

Search for a string inside all files in the current directory and subdirectories: grep -r "string" *

Search and replace within the file: sed -i '' 's/original-text/new-text/g' sample-filename.txt

MD5 hash for files: md5 sample-filename.txt

MD5 hash for folders: tar c folder | md5sum

Encrypt file: openssl enc -aes-256-cbc -e -in sample-filename.txt -out sample-encrypted.txt

Decrypt file: openssl enc -aes-256-cbc -d -in sample-encrypted.txt -out sample-filename.txt

Server

Access via ssh: ssh pi@192.168.0.0

Copy file from server to local: scp pi@192.168.0.0:/path/to/file.png ~/Desktop/ (use -r to recursively get complete folder)

Copy file from local to server: scp ~/Desktop/file.png pi@192.168.0.0:/path/to/folder (use -r to recursively get complete folder)

Copy file from local to server: rsync --exclude=".DS_Store" -vzcrSLh ~/Desktop/file.png pi@192.168.0.0:/path/to/folder

Escape files with spaces in the name like this: /path/to/file\\\ name.png

System

Show disc space: df -h

Show disc space (inodes): df -i

Show disc space for current directory: du -hs

Current processes (also CPS usage): top or htop

Show running PHP processes: ps aux | grep php

Monitor error log (stream as the file grows): tail error.log -f -n 0

Apps

Start application: open -a [name-of-programm] e.g. open -a firefox

Open finder with current folder: open .

Variables

Register variable: export TESTING="Sample Text"

Echo variable: echo $TESTING

Unset variable: unset TESTING

Output & Redirects

Write to file: echo "Hello" > hello.txt

Append content from a file to another file: cat file1.txt >> file2.txt

Add the number of lines, words, and characters to file2.txt: cat file1.txt | wc | cat > file2.txt

Sort the content of a file (like cat): sort hello.txt

Save to sorted content to a new file: cat file1.txt | sort > sorted-file1.txt

Sort and remove duplicates and save them to a new file: sort file1.txt | uniq > uniq-file1.txt

Functions

Calculate (returns only int): echo $((123/2))

HTTP

Check site feedback: ping google.com

Show site IP: dig +short google.com

Show A Record: dig a google.com (Returns: google.com. 43 IN A 123.123.123.123 aka public-name ttl internet record-type server-address)

Webservice: https://www.whatsmydns.net/

Curl headers: curl -I https://hofmannsven.com

Tools

Tree

Installation: brew install tree

HTTPie

Installation: brew install httpie

Usage:

http GET https://hofmannsven.test --verify=no

Security

Fix OpenSSH Client Bug: https://www.digitalocean.com/community/questions/openssh-client-bug-cve-2016-0777-and-cve-2016-0778

Signing off:

Akshay Prasad