How to escape single quotes within single quoted strings

If you really want to use single quotes in the outermost layer, remember that you can glue both kinds of quotation. Example:

 alias rxvt='urxvt -fg '"'"'#111111'"'"' -bg '"'"'#111111'"'"
 #                     ^^^^^       ^^^^^     ^^^^^       ^^^^
 #                     12345       12345     12345       1234

Explanation of how '"'"' is interpreted as just ':

1. ' End first quotation which uses single quotes.
2. " Start second quotation, using double-quotes.
3. ' Quoted character.
4. " End second quotation, using double-quotes.
5. ' Start third quotation, using single quotes.

If you do not place any whitespaces between (1) and (2), or between (4) and (5), the shell will interpret that string as a one long word.

I don't see the entry on his blog (link pls?) but according to the gnu reference manual:

Enclosing characters in single quotes (‘'’) preserves the literal value of each character within the quotes. A single quote may not occur between single quotes, even when preceded by a backslash.

so bash won't understand:

alias x='y \'z '

however, you can do this if you surround with double quotes:

alias x="echo \'y "
> x
> 'y

How to escape single quotes (') and double quotes (") with hex and octal chars

If using something like echo, I've had some really complicated and really weird and hard-to-escape (think: very nested) cases where the only thing I could get to work was using octal or hex codes!

Here are some basic examples just to demonstrate how it works:

1. Single quote example, where ' is escaped with hex \x27 or octal \047 (its corresponding ASCII code):

1. hex \x27

   echo -e "Let\x27s get coding!"
   # OR
   echo -e 'Let\x27s get coding!'
   

   Result:

   Let's get coding!
   

2. octal \047

   echo -e "Let\047s get coding!"
   # OR
   echo -e 'Let\047s get coding!'
   

   Result:

   Let's get coding!
   

2. Double quote example, where " is escaped with hex \x22 or octal \042 (its corresponding ASCII code).

Note: bash is nuts! Sometimes even the ! char has special meaning, and must either be removed from within the double quotes and then escaped "like this"\! or put entirely within single quotes 'like this!', rather than within double quotes.

# 1. hex; also escape `!` by removing it from within the double quotes 
# and escaping it with `\!`
$ echo -e "She said, \x22Let\x27s get coding"\!"\x22"
She said, "Let's get coding!"

# OR put it all within single quotes:
$ echo -e 'She said, \x22Let\x27s get coding!\x22'
She said, "Let's get coding!"


# 2. octal; also escape `!` by removing it from within the double quotes 
$ echo -e "She said, \042Let\047s get coding"\!"\042"
She said, "Let's get coding!"

# OR put it all within single quotes:
$ echo -e 'She said, \042Let\047s get coding!\042'
She said, "Let's get coding!"


# 3. mixed hex and octal, just for fun
# also escape `!` by removing it from within the double quotes when it is followed by
# another escape sequence
$ echo -e "She said, \x22Let\047s get coding! It\x27s waaay past time to begin"\!"\042"
She said, "Let's get coding! It's waaay past time to begin!"

# OR put it all within single quotes:
$ echo -e 'She said, \x22Let\047s get coding! It\x27s waaay past time to begin!\042'
She said, "Let's get coding! It's waaay past time to begin!"

Note that if you don't properly escape !, when needed, as I've shown two ways to do above, you'll get some weird errors, like this:

$ echo -e "She said, \x22Let\047s get coding! It\x27s waaay past time to begin!\042"
bash: !\042: event not found

OR:

$ echo -e "She said, \x22Let\x27s get coding!\x22"
bash: !\x22: event not found

One more alternative: this allows mixed expansion and non-expansion all within the same bash string

Here is another demo of an alternative escaping technique.

First, read the main answer by @liori to see how the 2nd form below works. Now, read these two alternative ways of escaping characters. Both examples below are identical in their output:

CMD="gs_set_title"

# 1. 1st technique: escape the $ symbol with a backslash (\) so it doesn't 
# run and expand the command following it
echo "$CMD '\$(basename \"\$(pwd)\")'"

# 2. 2nd technique (does the same thing in a different way): escape the 
# $ symbol using single quotes around it, and the single quote (') symbol
# using double quotes around it
echo "$CMD ""'"'$(basename "$(pwd)")'"'"

Sample output:

gs_set_title '$(basename "$(pwd)")'
gs_set_title '$(basename "$(pwd)")'

Note: for my gs_set_title bash function, which I have in my ~/.bash_aliases file somewhere around here, see my other answer here.

References:

1. https://en.wikipedia.org/wiki/ASCII#Printable_characters
2. https://serverfault.com/questions/208265/what-is-bash-event-not-found/208266#208266
3. See also my other answer here: How do I write non-ASCII characters using echo?.

A minimal answer is needed so that people can get going without spending a lot of time as I had to sifting through people waxing eloquent.

There is no way to escape single quotes or anything else within single quotes.

The following is, perhaps surprisingly, a complete command:

$ echo '\'

whose output is:

\

Backslashes, surprisingly to even long-time users of bash, have no meaning inside single quotes. Nor does anything else.

In the given example, simply used double quotes instead of single quotes as outer escape mechanism:

alias rxvt="urxvt -fg '#111111' -bg '#111111'"

This approach is suited for many cases where you just want to pass a fixed string to a command: Just check how the shell will interpret the double-quoted string through an echo, and escape characters with backslash if necessary.

In the example, you'd see that double quotes are sufficient to protect the string:

$ echo "urxvt -fg '#111111' -bg '#111111'"
urxvt -fg '#111111' -bg '#111111'

in addition to @JasonWoof perfect answer i want to show how i solved related problem

in my case encoding single quotes with '\'' will not always be sufficient, for example if a string must quoted with single quotes, but the total count of quotes results in odd amount

#!/bin/bash

# no closing quote
string='alecxs\'solution'

# this works for string
string="alecxs'solution"
string=alecxs\'solution
string='alecxs'\''solution'

let's assume string is a file name and we need to save quoted file names in a list (like stat -c%N ./* > list)

echo "'$string'" > "$string"
cat "$string"

but processing this list will fail (depending on how many quotes the string does contain in total)

while read file
  do
    ls -l "$file"
    eval ls -l "$file"
done < "$string"

workaround: encode quotes with string manipulation

string="${string//$'\047'/\'\$\'\\\\047\'\'}"

# result
echo "$string"

now it works because quotes are always balanced

echo "'$string'" > list
while read file
  do
    ls -l "$file"
    eval ls -l "$file"
done < list

Hope this helps when facing similar problem

shell_escape () {
    printf '%s' "'${1//\'/\'\\\'\'}'"
}

Implementation explanation:

• double quotes so we can easily output wrapping single quotes and use the ${...} syntax

• bash's search and replace looks like: ${varname//search/replacement}

• we're replacing ' with '\''

• '\'' encodes a single ' like so:

  1. ' ends the single quoting

  2. \' encodes a ' (the backslash is needed because we're not inside quotes)

  3. ' starts up single quoting again

  4. bash automatically concatenates strings with no white space between

• there's a \ before every \ and ' because that's the escaping rules for ${...//.../...} .

string="That's "'#@$*&^`(@#'
echo "original: $string"
echo "encoded:  $(shell_escape "$string")"
echo "expanded: $(bash -c "echo $(shell_escape "$string")")"

P.S. Always encode to single quoted strings because they are way simpler than double quoted strings.

Here are my two cents -- in the case if one wants to be sh-portable, not just bash-specific ( the solution is not too efficient, though, as it starts an external program -- sed ):

• put this in quote.sh ( or just quote ) somewhere on your PATH :

# this works with standard input (stdin)
quote() {
  echo -n "'" ;
  sed 's/\(['"'"']['"'"']*\)/'"'"'"\1"'"'"'/g' ;
  echo -n "'"
}

case "$1" in
 -) quote ;;
 *) echo "usage: cat ... | quote - # single-quotes input for Bourne shell" 2>&1 ;;
esac

An example:

$ echo -n "G'day, mate!" | ./quote.sh -
'G'"'"'day, mate!'

And, of course, that converts back:

$ echo 'G'"'"'day, mate!'
G'day, mate!

Explanation: basically we have to enclose the input with quotes ', and then also replace any single quote within with this micro-monster: '"'"' ( end the opening quote with a pairing ', escape the found single quote by wrapping it with double quotes -- "'", and then finally issue a new opening single quote ', or in pseudo-notation : ' + "'" + ' == '"'"' )

One standard way to do that would be to use sed with the following substitution command:

s/\(['][']*\)/'"\1"'/g 

One small problem, though, is that in order to use that in shell one needs to escape all these single quote characters in the sed expression itself -- what leads to something like

sed 's/\(['"'"']['"'"']*\)/'"'"'"\1"'"'"'/g' 

( and one good way to build this result is to feed the original expression s/\(['][']*\)/'"\1"'/g to Kyle Rose' or George V. Reilly's scripts ).

Finally, it kind of makes sense to expect the input to come from stdin -- since passing it through command-line arguments could be already too much trouble.

( Oh, and may be we want to add a small help message so that the script does not hang when someone just runs it as ./quote.sh --help wondering what it does. )

If you have GNU Parallel installed you can use its internal quoting:

$ parallel --shellquote
L's 12" record
<Ctrl-D>
'L'"'"'s 12" record'
$ echo 'L'"'"'s 12" record'
L's 12" record

From version 20190222 you can even --shellquote multiple times:

$ parallel --shellquote --shellquote --shellquote
L's 12" record
<Ctrl-D>
'"'"'"'"'"'"'L'"'"'"'"'"'"'"'"'"'"'"'"'"'"'"'"'"'"'"'"'"'"'"'"'"'"'s 12" record'"'"'"'"'"'"'
$ eval eval echo '"'"'"'"'"'"'L'"'"'"'"'"'"'"'"'"'"'"'"'"'"'"'"'"'"'"'"'"'"'"'"'"'"'s 12" record'"'"'"'"'"'"'
L's 12" record

It will quote the string in all supported shells (not only bash).