Linux Command Line Basic and Shell

Go Into the Shell

Environment: VirtualBox + Vagrant + Git Bash

Terminal and Shell:

• Terminal (emulator) displays your keyboard input and the output, but itself do not know how to handle your input
• Shell will accept the input transferred from Terminal, run the command and then send the output to Terminal to display
  • Default shell on Linux and Mac is GNU Bash
  • Can also use such as Python interpreter instead of shell

Some Commands: a bit like calling a Python function (but shell is used to run a program, function is used to organize a program)

date
expr 2 + 2		# run program, not organize program
echo You rock
uname	# print OS name
hostname
host udacity.com
bash --version		# most command has --version or -V
history		# typed commands

Shell Command

echo:

• echo $COLUMNS x $LINES outputs info with variable

Command History:

• Up arrow
• history
• Ctrl+R for used command search

File Related:

• ls, by default hide file starting with . (normally store cache or configuration which is not interesting)
  • ls ~ for home dir
• curl for download anything
  • curl -o dictionary.txt -L 'http://t.cn/RYkeaZi', always keep link inside single quotes
• unzip
• cat for concatenate, outputing multiple (small) files
• less for display file screen by screen
  • / for search
  • q for quit
• grep for search in file
• nano for edit the file (integrated in ubuntu)
• wc for word counts
• diff for version comparison
• rm
  • -i for interactive to confirm
  • -r for recursively delete all files under dir
  • -f for ignoring warning
• apropos for list of commands related to particular keywords, for example, apropos working directory

man + command command: get detailed information of certain command

PS: argument within [] is optional; and arguments are case sensitive

Line Based Programs: like ping (stop with Ctrl+C), sort (execute with Ctrl+D), bc (quit or Ctrl+D)

Full Screen Interactive Programs: like man, less for displaying long file

Output Result to a File:

echo 'Hello World' >> demo.txt		# append to demo.txt
echo 'Brand New' > demo.txt		# overwrite demo.txt

Pipe Commands:

grep ibo dictionary.txt | less		# search ibo in a txt file, and packages the output and send to less
curl -L 'https://tinyurl.com' | grep fish		# download from a url and search fish in this file

Variable:

• Define just like that in Python, and call it with $ (variable interpolation)
• Shell variable: like $COLUMNS
• Environment variable: like $PWD or $LOGNAME
  • $PATH variable stores path of your program files, like path of ls
    • For the exact path of ls, use which ls

The Linux Filesystem

File Name: do not have requirement of file name, and even not require a file extension like Windows

Working Directory: Linux only has one drive:root, to store all files

• pwd for print working directory
• cd for change directory
  • cd .. for go outer dir
  • cd only for go to your home dir
• mkdir for create dir
• rmdir for remove EMPTY dir
  • rm -r to remove entities in dir

Absolute and Relative Path: start with / or not

Tab Completion: for file name and also dir

• One hit for completion, if there are more than one return, press Tab again to show all possible returns

Moving and Copying Files: mv and cp

• touch for create file

Globbing: 通配符

• * for anything, can be nothing also
• ? for any one character
• {item_1, item_2, ..} for multiple
• [aeiou] for any one character

Simple Bash Script

• Add the path of Notepad++ into SYSTEM PATH of windows
• Record down the path of bash by which bash (below takes /bin/bash as example)
• Run notepad++ file.sh
• In Notepad++

#!/bin/bash

echo 'Hello World'

• Check flag by ls -l, x in -rwxr-xr-x is executable
  • If not, use chmod +x file.sh
• Run with ./file.sh

Customize Your Shell

.bash_profile: run every time when shell start (or run source .bash_profile)

• can add in PATH of your own shell script, so that run it directly
• can display certain words when start

$PS1 Variable: for appearance of shell

• PS1 style generator
• setting with PS1 = "<code generated>"

alias: customize your command (can put into .bash_profile to fix)

alias ll = 'ls -la'
alias cl = 'curl -L'