Stripping single and double quotes in a string using bash / standard Linux commands only

Question

Hello Stack Overflow :-)

I'm looking for something that will translate a string as follows, using only bash / standard Linux commands:

1. Single-quotes surrounding a string should be removed
2. Double-quotes surrounding a string should be removed
3. Unquoted strings should remain the same
4. Strings with unmatched surrounding quotes should remain the same
5. Single-quotes that don't surround the string should remain
6. Double-quotes that don't surround the string should remain

For example:

• 'Food' should become Food
• "Food" should become Food
• Food should remain the same
• 'Food" should remain the same
• "Food' should remain the same
• 'Fo'od' should become Fo'od
• "Fo'od" should become Fo'od
• Fo'od should remain the same
• 'Fo"od' should become Fo"od
• "Fo"od" should become Fo"od
• Fo"od should remain the same

Thank you!

Answer 1

python -c "import sys;a=sys.stdin.read();a=a.strip();print (a[1:-1] if a[0]==a[-1] and a[0] in \"'\\\"\" else a)"

it doesn't handle edge cases extremely well (such as an empty string), but it will serve as a starting point. It works by striping the front and back character if they are the same and if they are ' or "

Answer 2

You probably want to use sed...

echo $mystring | sed -s "s/^\(\(\"\(.*\)\"\)\|\('\(.*\)'\)\)\$/\\3\\5/g"

Answer 3

This should do it:

sed "s/^\([\"']\)\(.*\)\1\$/\2/g" in.txt

Where in.txt is:

"Fo'od'
'Food'
"Food"
"Fo"od'
Food
'Food"
"Food'
'Fo'od'
"Fo'od"
Fo'od
'Fo"od'
"Fo"od"
Fo"od

And expected.txt is:

"Fo'od'
Food
Food
"Fo"od'
Food
'Food"
"Food'
Fo'od
Fo'od
Fo'od
Fo"od
Fo"od
Fo"od

You can check they match with:

diff -s <(sed "s/^\([\"']\)\(.*\)\1\$/\2/g" in.txt) expected.txt

Answer 4

echo $string | tr -d 'chars to delete' also works, however 'tr' is known to be problematic on much older distros.

Answer 5

Just using Bash builtins (i.e. Bash parameter expansion):

IFS=' ' 

food_strings=( "'Food'" '"Food"' Food "'Food\"" "\"Food'" "'Fo'od'" "\"Fo'od\"" "Fo'od" "'Fo\"od'" '"Fo"od"' 'Fo"od'  )  

for food in ${food_strings[@]}; do 

   [[ "${food#\'}" != "$food" ]] && [[ "${food%\'}" != "$food" ]] && { food="${food#\'}"; food="${food%\'}"; } 

   [[ "${food#\"}" != "$food" ]] && [[ "${food%\"}" != "$food" ]] && { food="${food#\"}"; food="${food%\"}"; } 

   echo "$food"

done

For yet another example of Bash parameter expansion see:

http://codesnippets.joyent.com/posts/show/1816