Using BASH

Bash is available by default on Mac and Linux and can be access via git-bash (installed when git is installed) on Windows. Bash is a "command line interpreter" meaning that it awaits your commands, usually one line at a time and executes them.

You know you are in a bash shell if you see a dollar ($) prompt with a blinking cursor awaiting your command.

Once you are at the bash prompt, you can find out who you are by typing $ whoami

This will print your username.

Next we can find out where in the filesystem we are by typing $ pwd

This will print the present working directory (within file system).

Here are some other basic commands to try out

  1. $ ls List the contents of the present working directory. You can also

    • $ls -a : lists all files including hidden ones.
    • $ls -l : list files with details

  2. $ cd <directory path> Change directory. If no directory name is specified then present working directory is set to your $HOME.

  3. $ cat <filename> Prints the content of file <filename>.

  4. $ man <command> Prints the manual for <command>.

Reference of basic commands

Use $man <command> to learn more about these commands and flags.

basic shell

  • clear : clear all previous commands' output text from the terminal
  • exit (or logout) : quits the shell
  • history : show a list of all past commands you have typed into this shell

manage directories

  • ls : list files in a directory
  • pwd : displays the shell's current working directory
  • cd : changes the shell's working directory to the given directory; can be a relative or absolute path
  • mkdir : creates a new directory with the given name
  • rmdir : removes the directory with the given name (the directory must be empty)

file operations

  • cp : copies a file/directory
  • mv : moves (or renames) a file/directory
  • rm : deletes a file
  • touch : update the last-modified time of a file (or create an empty file)
  • cat : output the contents of a file
  • more (or less) : output the contents of a file, one page at a time
  • head, tail : output the beginning or ending of a file
  • wc : output a count of the number of characters, lines, words, etc. in a file
  • du : report disk space used by a file/directory
  • diff : output differences between two files
  • chmod : change the permissions on a file or group of files
  • chown : change the owner of a file
  • chgrp : change the group associated with a file
  • umask : change the default permissions given to newly created files

searching and sorting

  • grep : search a file for a given string or expression
  • sort : convert an input into a sorted output
  • uniq : strip duplicate lines
  • find : search for files by name within a given directory
  • xargs : launch a command over each of a set of lines of input (often used with find)
  • locate : search for files by name on the entire system
  • which : shows the complete path of a command or file

compression

  • zip, unzip : create a .zip archive or extract its contents
  • tar : Unix archiving/de-archiving program
  • gzip, gunzip : GNU compression/decompression programs
  • bzip2, bunzip2 : improved compression/decompression programs

system information

  • date : outputs the current date/time
  • cal : outputs an ASCII calendar
  • uname : print information about the system
  • time : measure how long a program takes to run

process management

  • ps, jobs : list the processes you are running; every process has a unique integer id number (PID)
  • top : see what processes are using the most CPU/memory, and show system memory/CPU stats
  • kill : terminate a process
  • killall : terminate a group of processes by name
  • ^C: (hotkey) terminates (kills) the currently running process
  • ^Z : (hotkey) suspends the currently running process
  • & : (special character) when & is placed at the end of a command, that command is run in the background (shell does not wait for the command to finish before returning to the input prompt)

users

  • whoami : outputs your user name
  • passwd : changes your password
  • groups : list the groups to which a user belongs
  • sudo : execute a single command as the super-user
  • su : log in to a shell as the super-user

network

  • lynx : text-only web browser
  • ssh : connect to a remote Unix server
  • wget : download from a URL and save it to a file on the local hard drive
  • curl : download from a URL and output its contents to the console

text editors

  • vi, vim : good command line editor
  • emacs : a complicated text editor with a steep learning curve

programming

  • node : run a JavaScript program, or enter JS shell
  • javac, java, python, perl, ruby, gcc, sml, ... : compile or run programs in various other languages