Quotes

Reference http://wiki.bash-hackers.org/syntax/quoting

Per Character: \$HOME / \<newline> (line continuation)
Double Quote: "..."
- Escape:
  - spaces
  - single quotes
  - pattern matching characters and path name expansion (* / ? / {a,b,c})
  - process substitution (<(ls -l))
- Everything else remains (e.g. "$HOME" will be expanded)
- "\$" becomes $ but "\x" becomes \x
Single Quote: '...'
- Escape everything except '
  - Even '\$' becomes \$
- To use ...'..., must enter ...'\''... or ...'"'"'...
Localized String: $"..."
- Ignored when the locale is POSIX or C
ANSI C String: $'...'
- Use specific escape sequences similar to C:
  - \', \", \\
  - \a, \b, \e (ESC), \f, \n, \r, \t, \v
  - \c♥ (CTRL + ♥ where ♥ is some character)
  - \nnn (octal), \xHH (hex), \uXXXX (unicode)

Brackets

Reference http://stackoverflow.com/questions/2188199/how-to-use-double-or-single-bracket-parentheses-curly-braces

[ = test; the closing ] is optional
[[ = enhanced [ (e.g., can use || and && instead of -o and -a)
[...] = array index
- array[0]=value
- element=${array[0]}
{...}
- Brace expansion: {a,b,c} / {a..z}
- Code block: { date; make 2>&1; date; } | tee logfile
  - The last semicolon in {...} is mandatory
  - {...} must be surrounded by spaces
${...} = parameter expansion
- ${param:-word} = if param is not set, return word
- ${param:=word} = if param is not set, set it to word and return word
- ${paramr:offset} / ${param:offset:length} (negative indices work too)
- ${#param} = length
- ${param#prefix} / ${param##prefix} = remove shortest / longest prefix (mnemonic: # comes before $ on the keyboard)
- ${param%suffix} / ${param%%suffix} = remove shortest / longest suffix (mnemonic: % comes after $ on the keyboard)
- ${param/pattern/sub}
(...)
- Array: array=(1 2 3)
- Subshell: <(ls -l) / (cd .. && pwd) will not change directory in current shell
$(...) = command substitution (= backticks)
- result=$(COMMAND)
((...)) = arithmetic
- ((a++))
- ((meaning = 42))
- for ((i=0; i<10; i++))
- echo $((a + b + (14 * c)))