Master Essential Unix Commands: wget, scp, ssh-keygen, chmod, tar & Aliases

wget

On Unix‑like systems, wget downloads files via HTTP, HTTPS, or FTP. It is included in most Linux distributions. The simplest usage provides the URL of the file to retrieve:

wget http://website.com/static/images/header.jpg

wget

runs non‑interactively, allowing it to continue downloading after you log out.

scp

scp

(secure copy) transfers files between a local machine and a remote host over SSH. It works like cp but with a remote source or destination.

Copy a remote file to the local directory:

scp [email protected]:/path/to/foobar.txt /some/local/directory

Copy a local file to a remote server:

scp /some/local/directory/foobar.txt [email protected]:/destination/path/

Use the -r option to copy directories recursively.

ssh-keygen

The ssh-keygen command creates a new SSH key pair, which can be added to services such as GitLab or Bitbucket to enable password‑less pushes.

Generate an Ed25519 key pair (recommended): ssh-keygen -t ed25519 Research other signature algorithms if needed; the process typically takes a few minutes.

chmod

chmod

changes file system object permissions on Unix‑like operating systems. Correct permission settings are crucial for security and functionality.

Example: grant read/write permissions to the user and group for robots.txt: chmod 664 robots.txt Example: give user and group read/write/execute on public/images, others read/execute: chmod 775 public/images Refer to the Wikipedia page for detailed mode specifications.

tar

tar

creates and extracts archive files. To archive a directory: tar -cvf my-archive.tar /path/to/directory To extract the archive to a specific location:

tar -xvf my-archive.tar -C /home/myfolder/

alias

Aliases let you define short names for long commands, improving workflow. A temporary alias for the current session:

alias short-command="your custom and very long command here"

To make an alias persistent, add it to your shell’s configuration file (e.g., ~/.bashrc or ~/.zshrc).

Output Redirection and Command Chaining

Redirect command output to a file using >: ls -al > myfile Combine multiple commands with a semicolon ( ;) to run them sequentially regardless of success: ls -al; pwd; Run the second command only if the first succeeds using logical AND ( &&), or only if the first fails using logical OR ( ||).

mkdir images && cd images