Terminal-Cheatsheet

My personal cheatsheet for the Mac OS Terminal

The Shell

In order to use commands you'll need a program that reads and executes them. That program is called shell, which runs inside the Terminal. Some commands are builtin and some commands are external programs. You can check that by using the type command.

Command	Output
type ls	ls is an alias for ls -G
type pod	pod is Users/username/.rvm/gems/ruby-2.0.0-p247/bin/pod

Wildcards

Command	Description
ls a*	List all Files that begin with lowercase a
ls *20	List files that end with 20

Shell variables

You can define a shell variables and their values by assigning them:

VAR=3 

Print it out using a leading $

echo $VAR

The Shell comes with some default Variables.

Variables	Description
DISPLAY	The name of your display for opening X Windows
HOME	Your home directory
LOGNAME	Your login name
MAIL	Your incoming mailbox
OLDPWD	You shells's previous directory, prior to the last cd command
PATH	Your shell search path: directories separate by colons
PWD	Your shells current directory
SHELL	The path to your shell
TERM	The type of your terminal
USER	Your login name

Use printenv to print all of them. If you want to create an environment variable that is available to all programms started from that shell you need to use

export VAR=3 

or

export VAR

if you previously defined VAR.

Search path

Programs are scattered all over the filesystem, in directories like /bin and /usr/bin. The variable PATH tells the shell where to look.PATH is a sequence of directories separated by colons

Modify it using: PATH=$PATH:/your/directory

if you want to make it permanent you need to put that command into your .bash_profile or .zshrc

Aliases

alias ll='ls -l'

unalias ll

Input & Output redirection

The shell can redirect standard in, standard out and standard error to and from files. Any command that reads from standard input can read from a file instead with the shells <, > and 2> operator

Command	Description
command < infile	command should read from file
command > outfile	command should write to a file
command >> outfile	command should append its output to file
command 2> errorfile	write standard error to file & stream
command > outfile 2> errorFile	write to outfile and things the command writes to stderror will be redirected to errorFile

Pipes

Redirection of standard input of one command can be redirected to another command using the | operator.

Command	Description
ls | wc -l	redirect ls output to word count command
ls -1 | cut -d. -f2 | sort	Show all file types

Combining Commands

Command	Description
command1 ; command2	If anyone fails, the sequence continues
command1 && command2	The sequence will stop if any command fails
command1 || command2	The sequence will stop if one command succeeded

Quoting & Escaping

If you want a word contain whitspaced you need to surround it with single or double quotes to make the shell treat it as a unit. Double quotes will result in evaluating the actual content and replacing shell variables with there actual content.

Command	Description
wc 'Value of PATH: $PATH'	Will print "Value of PATH: $PATH"
wc "Value of PATH: $PATH"	Will print "Value of PATH: /users/sebastian/.."

If a character has a special meaning to the shell but you want it used literally, precede the character with a backslash \

Command	Description
echo a\*	Will print a*, so * will not be interpreted as the wildcard symbol

Command History

The shell allows you to recall previous commands. All commands you are entered are stored inside the command history. Here are some handy command you can use for it

Command	Description
history	print your history
history N	print most recent n commands
history -c	clear your history
!!	re run previous command
!N	rerun command N in history
!-N	rerun command you typed n times ago
!$	last parameter from previous command
!*	all parameters from last command
up arrow	go to previous command
down arrow	go to next command

Jobs

All shells have job control: the ability to run programs in the background (multitasking) und foreground (running as the active process at your shell). Jobs are higher level than processes.

Command	Description
jobs	List your Jobs
emacs myfile &	put emacs to the background
^Z	suspend the current forground job
bg [%jobnumber]	send suspended job to the background
fg [%jobnumber]	bring it into the foreground
suspend	make supsended job run in the background

Filesystem

Command	Description
cd	change to your home directory
cd /dir	change to dir
cd ../dir	change to parents sub directory dir
cd ./dir	change to current sub directory dir
pwd	print name of current working directory
echo ~	print path of home directory

File Protection

Example:

-rw-r--r--

Postion	Meaning
1	File type. -(plain file), d(Directory), l(symbolic link), p(named Pipe), c(character device) b(block device)
2-4	Owner permissions, read, write, and execute permissions for the files's owner
5-7	Group permissions, read, write, and execute permissions for the files's group
8-10	World permissions, read, write, and execute permissions for all other users

Commands

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