UNIX I Cheat Sheet

Definition
Command line interpreter program that functions as the default interface when you connect to a server over a network
bash
Default shell on Ubuntu and OSX. "Bourne-again shell."
Terminal Prompt
`user>@host:path$`
`user`	Logged in user name
`host`	Machine name
`path`	File system position
`$`	Symbol (e.g. `$` bash)

About
`cmd -help`	Full usage for `cmd`
`whatis cmd`	One-line explanation of `cmd`
`man cmd`	Manual for `cmd` if available
`info cmd`	Info about `cmd` ; use if `man` is unavailable
`str [2x tab]`	List commands with `str` prefix
History
`history n`	Show last `n` commands
`!!`	Repeat last command
`!str`	Repeat last command with `str` prefix
`up arrow`	Scroll through history list
Directing Output
`cmd >> file`	Append output of `cmd` to `file`
`cmd > file`	Overwrite `file` with output of `cmd`
`cmd1 \| cmd2 ...`	Direct output of `cmd1` to `cmd2`
Example `$ echo "My new note" >> notes.txt $ cat notes.txt # My new note`

Absolute Path
Route to desired dir. Always starts w slash or tilde, e.g. `/home/john/myfile.txt`
Relative Path
From working dir. Never starts w slash, e.g. `john/myfile.txt`
Shortcuts
`..`	Path of parent dir of current working dir
`.`	Path of current working dir
`~`	Path of home dir, e.g. `$ echo ~ # user@host:/home/user/`
`~user`	Another user's home dir
`/`	Root
Environmental Variables
`$OLDPWD`	Previous working dir
`$PATH`	Ordered, colon-delimited list of dirs in search when call is made from working dir
	Parsing Colon-delimited; use `tr` to replace, e.g. `$ echo $PATH \| tr ":" "\n"`
	Home Directory Home dir (e.g. `/home/john` ) is never in path, but its subdirs may be if working dir is a subdir of home.
`$PYTHONPATH`	Python modules
Useful Commands
`pwd`	Print working dir
`cd dir`	Move working dir to `dir`
`-`	To previous wd (i.e. `$OLDPATH` )
`ls dir`	List `dir` contents
`-l`	Get a long list - permissions, links count,
`-F`	Indicate file type `*` exe `/` dir
`-b`	Print special chars, including - `\| & ' ; ( ) < > space tab`
`-a`	All including hidden files with `.` prefix
`-1`	All output in one column
`-R`	Recursive; include subdirs and contents
`-r`	Reverse sort order
`-t`	Sort by most recent modified
`-d`	Dirs only
`find dir opts`	Search `dir` and its subdirs for file specified by `opts` expression, e.g. `$ find . -name 'chap*' $ find . -mtime -2 $ find . -user john`

Configuration
Update hidden programs run at login/shell start.
`.bashrc`	Run with interactive bash shell
`.bash_profile`	Run at bash login before `.profile`
`.profile`	Run at login by most UINX shells
Example
Add lib to `$PYTHONPATH` in `~/.bashrc` with `export PYTHONPATH=/home/john/module/lib$PYTHONPATH`
Useful Commands
`ssh user@host`	connect to `host` as `user`
`whoami`	who you are logged in as
`passwd`	set password
`exit`	logout of session and close terminal

Useful Commands
`chmod`	Change permissions mode
	Usage
	`$ chmod [ugoa][+-=][rwx], …, [path]`
	Groups
	`u`	User owner	`o`	Other/system
	`g`	Group	`a`	All
	Change Operator
	`+`	Add
	`-`	Remove
	`=`	Set Explicit
	Mode
	`r, 4`	Read	`x, 1`	Execute file
	`w, 2`	Write	`x, 1`	Access dir
	Octal
	`0`	`---`	`4`	`r--`
	`1`	`--x`	`5`	`r-x`
	`2`	`-w-`	`6`	`rw-`
	`3`	`-wx`	`7`	`rwx`
	Examples
	Both the following examples grant all permissions to the owner of bin and read + execute permissions to the owner's group and others. `$ chmod u=rwx,go=rx /home/john/bin` `$ chmod 755 /home/john/bin`

UNIX I Cheat Sheet (DRAFT) by birdbysnow