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How to escape quotes in shell?


You can use the following string literal syntax:

> echo $''single quote phrase' "double quote phrase"'
'single quote phrase' "double quote phrase"

From man bash

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

          a     alert (bell)
          b     backspace
          E     an escape character
          f     form feed
          n     new line
          r     carriage return
          t     horizontal tab
          v     vertical tab
          \     backslash
          '     single quote
          "     double quote
          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)
          cx    a control-x character

Simple example of escaping quotes in shell:

$ echo 'abc'''abc'
$ echo "abc"""abc"

It’s done by finishing already opened one ('), placing escaped one ('), then opening another one (').


$ echo 'abc'"'"'abc'
$ echo "abc"'"'"abc"

It’s done by finishing already opened one ('), placing quote in another quote ("'"), then opening another one (').

Related: How to escape single-quotes within single-quoted strings? at stackoverflow SE

In a POSIX shell, assuming in your string there is no variable, command or history expansion, and there is no newline, follow these basic prescriptions:

  1. To quote a generic string with single quotes, perform the following actions:

    1. Substitute any sequence of non-single-quote characters with the same sequence with added leading and trailing single quotes: 'aaa' ==> ''aaa''

    2. Escape with a backslash every preexisting single quote character: ' ==> '
      In particular, ''aaa'' ==> ''aaa''

  2. To quote a generic string with double quotes, perform the following actions:

    1. Add leading and trailing double quotes: aaa ==> "aaa"

    2. Escape with a backslash every double quote character and every backslash character: " ==> ", ==> \

A couple of examples:

''aaa""bbb''ccc\ddd''  ==>  '''aaa""bbb''''ccc\ddd'''
                        ==>  "''aaa""bbb''ccc\\ddd''"

so that you example could be expanded with the following:


echo ''aaa''' "bbb"'
echo "'aaa' "bbb""

sudo su enzotib -c 'echo ''''aaa''''''' "bbb"''
sudo su enzotib -c 'echo "'''aaa''' "bbb""'

sudo su enzotib -c "echo \''aaa'\'' "bbb"'"
sudo su enzotib -c "echo "'aaa' \"bbb\"""

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