How to escape single quotes within single quoted strings

Question

Let\'s say, you have a Bash alias like:

alias rxvt=\'urxvt\'

which works fine.

However:

Answer 1

Since Bash 2.04 syntax $'string' (instead of just 'string'; warning: do not confuse with $('string')) is another quoting mechanism which allows ANSI C-like escape sequences and do expansion to single-quoted version.

Simple example:

  $> echo $'aa\'bb'
  aa'bb

  $> alias myvar=$'aa\'bb'
  $> alias myvar
  alias myvar='aa'\''bb'

In your case:

$> alias rxvt=$'urxvt -fg \'#111111\' -bg \'#111111\''
$> alias rxvt
alias rxvt='urxvt -fg '\''#111111'\'' -bg '\''#111111'\'''

Common escaping sequences works as expected:

\'     single quote
\"     double quote
\\     backslash
\n     new line
\t     horizontal tab
\r     carriage return

---

Below is copy+pasted related documentation from man bash (version 4.4):

Words of the form $'string' are treated specially. The word expands to string, with backslash-escaped characters replaced as specified by the ANSI C standard. Backslash escape sequences, if present, are decoded as follows:

    \a     alert (bell)
    \b     backspace
    \e
    \E     an escape character
    \f     form feed
    \n     new line
    \r     carriage return
    \t     horizontal tab
    \v     vertical tab
    \\     backslash
    \'     single quote
    \"     double quote
    \?     question mark
    \nnn   the eight-bit character whose value is the octal 
           value nnn (one to three digits)
    \xHH   the eight-bit character whose value is the hexadecimal
           value HH (one or two hex digits)
    \uHHHH the Unicode (ISO/IEC 10646) character whose value is 
           the hexadecimal value HHHH (one to four hex digits)
    \UHHHHHHHH the Unicode (ISO/IEC 10646) character whose value 
               is the hexadecimal value HHHHHHHH (one to eight 
               hex digits)
    \cx    a control-x character

The expanded result is single-quoted, as if the dollar sign had not been present.

---

See Quotes and escaping: ANSI C like strings on bash-hackers.org wiki for more details. Also note that "Bash Changes" file (overview here) mentions a lot for changes and bug fixes related to the $'string' quoting mechanism.

According to unix.stackexchange.com How to use a special character as a normal one? it should work (with some variations) in bash, zsh, mksh, ksh93 and FreeBSD and busybox sh.