Bash Quotes and Brackets

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)))
Exported: 2016-07-13T01:32:25.392295