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

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. )

Answer 2

Here is an elaboration on The One True Answer referenced above:

Sometimes I will be downloading using rsync over ssh and have to escape a filename with a ' in it TWICE! (OMG!) Once for bash and once for ssh. The same principle of alternating quotation delimiters is at work here.

For example, let's say we want to get: Louis Theroux's LA Stories ...

1. First you enclose Louis Theroux in single quotes for bash and double quotes for ssh: '"Louis Theroux"'
2. Then you use single quotes to escape a double quote '"'
3. The use double quotes to escape the apostrophe "'"
4. Then repeat #2, using single quotes to escape a double quote '"'
5. Then enclose LA Stories in single quotes for bash and double quotes for ssh: '"LA Stories"'

And behold! You wind up with this:

rsync -ave ssh '"Louis Theroux"''"'"'"'"''"s LA Stories"'

which is an awful lot of work for one little ' -- but there you go

Answer 3

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

Answer 4

Here is another solution. This function will take a single argument and appropriately quote it using the single-quote character, just as the voted answer above explains:

single_quote() {
  local quoted="'"
  local i=0
  while [ $i -lt ${#1} ]; do
    local ch="${1:i:1}"
    if [[ "$ch" != "'" ]]; then
      quoted="$quoted$ch"
    else
      local single_quotes="'"
      local j=1
      while [ $j -lt ${#1} ] && [[ "${1:i+j:1}" == "'" ]]; do
        single_quotes="$single_quotes'"
        ((j++))
      done
      quoted="$quoted'\"$single_quotes\"'"
      ((i+=j-1))
    fi
    ((i++))
  done
  echo "$quoted'"
}

So, you can use it this way:

single_quote "1 2 '3'"
'1 2 '"'"'3'"'"''

x="this text is quoted: 'hello'"
eval "echo $(single_quote "$x")"
this text is quoted: 'hello'

Answer 5

If you're generating the shell string within Python 2 or Python 3, the following may help to quote the arguments:

#!/usr/bin/env python

from __future__ import print_function

try:  # py3
    from shlex import quote as shlex_quote
except ImportError:  # py2
    from pipes import quote as shlex_quote

s = """foo ain't "bad" so there!"""

print(s)
print(" ".join([shlex_quote(t) for t in s.split()]))

This will output:

foo ain't "bad" so there!
foo 'ain'"'"'t' '"bad"' so 'there!'

Answer 6

I just use shell codes.. e.g. \x27 or \\x22 as applicable. No hassle, ever really.