Best quotes practice when it doesn't matter? [closed]

Question

If I want to something like:

foo="bar baz"
foo='bar baz'

Is it best practice to use double-quotes or single-quotes?

Answer 1

It depends, as usual:

• Single quotes cannot contain other single quotes, and there's no way to escape them. For this reason they should only be used for 'simple' text.
• Double quotes support useful things like brace expansion (echo "${USER} uses ${LANG#*.} encoding"), but you can't include escape sequences in them. That means you generally won't be able to see the difference between for example "[space][tab]" and "[tab]" strings.

• Dollar-single quoted strings are much like double-quoted strings, but can contain control characters. My personal favorite for unit testing:

  $ echo -n $'--$`!*@\a\b\E\f\r\t\v\\\'"\360\240\202\211 \n' | uniname -bcepu
  glyph   name
  -      HYPHEN-MINUS
  -      HYPHEN-MINUS
  $      DOLLAR SIGN
  `      GRAVE ACCENT
  !      EXCLAMATION MARK
  *      ASTERISK
  @      COMMERCIAL AT
          BELL
          BACKSPACE
          ESCAPE
          FORM FEED (FF)
          CARRIAGE RETURN (CR)
          CHARACTER TABULATION
          LINE TABULATION
  \      REVERSE SOLIDUS
  '      APOSTROPHE
  "      QUOTATION MARK
  𠂉      Unknown character in range CJK Unified Ideographs Extension B
          SPACE
          LINE FEED (LF)
  

If you want to know if you should use $' quoting or not for a variable, try sending it to printf %q:

$ var=foo
$ printf %q "$var"
foo
$ var="foo
> bar"
$ printf %q "$var"
$'foo\nbar'