grep, vim and Bash cheat sheet

The chapter on one page: what to remember, the operators, patterns and keys to have at your fingertips, and flashcards for quick revision.

The chapter in eight sentences

Every command has stdin (0), stdout (1) and stderr (2); output and errors both reach the terminal unless you redirect them.
> replaces a file, >> appends, 2> captures errors, &> captures both, and /dev/null throws anything away.
A pipe | feeds one command's stdout into the next command's stdin; tee saves a copy on the way.
grep prints matching lines; -i, -v, -n, -c, -w, -r and -l change what and how, and -E enables +, ?, {n,m}, | and ( ).
In regular expressions, ^ and $ anchor, . is any character, * repeats, and […] is one character from a set.
vim starts in normal mode: i to insert, Esc to stop, :wq to save and quit, :q! to give up, u to undo.
Variables are set with NAME=value and read with $NAME; only exported variables reach the programs you start, and PATH decides where commands are found.
Aliases and settings last for one shell unless you put them in ~/.bashrc (aliases, prompt, history) or ~/.bash_profile (exported variables); /etc/profile.d applies to everyone.

Write	Means
`cmd > file`, `cmd >> file`	stdout to a file: replace, append
`cmd 2> file`, `cmd 2>> file`	stderr to a file
`cmd &> file` (`> file 2>&1`)	both to one file
`cmd 2> /dev/null`	discard errors
`cmd < file`	stdin from a file
`cmd1 \| cmd2`	stdout of cmd1 into stdin of cmd2
`cmd \| tee file \| cmd2`	save a copy and pass it on (`-a` appends)

Write	Means
`grep -i`, `-v`, `-n`, `-c`	ignore case, invert, number lines, count
`grep -w`, `-r`, `-l`, `-E`	whole words, recurse, file names only, extended
`^`, `$`, `^$`	start, end, empty line
`.`, `.*`, `[abc]`, `[^abc]`, `[[:digit:]]`	any char, anything, set, not in set, class
`\<`, `\>`	start, end of a word
`-E`: `+` `?` `{n,m}` `a\|b` `( )`	one or more, optional, count, either, group

Keys	Do
`i` `a` `o`, `Esc`	insert before / after / new line, back to normal
`:w`, `:wq`, `:q!`	save, save and quit, quit discarding
`x`, `dd`, `yy`, `p`	delete char, cut line, copy line, paste
`u`, `Ctrl+R`	undo, redo
`gg`, `G`, `:N`	first line, last line, line N
`/text`, `n`	search, next match
`:%s/old/new/g`	replace everywhere
`v`, `V`, `Ctrl+V`	select characters, lines, block

Write	Means
`NAME=value`, `$NAME`, `${NAME}`	set, read, read next to other text
`export NAME`, `export NAME=value`	make it an environment variable
`unset NAME`, `env`, `set`	remove, list environment, list all
`NAME=value cmd`	set it for one command
`export PATH=$PATH:/dir`	add a directory to the command search
`alias name='cmd'`, `unalias name`	create, remove an alias
`~/.bashrc`, `~/.bash_profile`, `/etc/profile.d/*.sh`	personal per shell, personal per login, everyone
`source ~/.bashrc`	apply to the current shell

The three standard streams and their numbers?: stdin **0**, stdout **1**, stderr **2**.
Append output to a file instead of replacing it?: `>>`
Hide a command's error messages?: `cmd 2> /dev/null`
Save a pipeline's data to a file and keep it flowing?: `… | tee file | …`
Show lines that do not match a pattern?: `grep -v PATTERN`
What do ^ and $ mean in a regular expression?: The start and the end of the line.
What does .* match?: Any characters, any number of times, including none.
Which grep option makes +, ?, | and ( ) work without backslashes?: `-E` (extended regular expressions)
vim is doing odd things when you type. First move?: Press **Esc** to get back to normal mode.
Quit vim and discard your changes?: `:q!`
Copy a line and paste it below in vim?: `yy` then `p`
Make a variable visible to programs you start?: `export NAME`
Where do personal aliases go?: `~/.bashrc`
Apply an edited ~/.bashrc to the current shell?: `source ~/.bashrc`