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


Question

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!

1
20
4/16/2009 9:05:13 PM

Accepted Answer

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
32
4/17/2009 4:51:47 AM

You could use tr:

echo "$string" | tr -d 'chars to delete' 

... also works, however 'tr' is known to be problematic on much older (circa Redhat 9-ish) distributions. tr is an abbreviation for 'translate', commonly used in pipes to transform input. The -d option simply means 'delete'.

Most modern versions also contain predefined macros to transform upper to lower, lower to upper, kill white space, etc. Hence, if you use it, take a second to poke at what else it does (see the help output / man page), comes in handy.


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