Replace every " within string - sed

Question

I have lines in a text file which looks like this example:
"2009217",2015,3,"N","N","2","UPPER DARBY FIREFIGHTERS "PAC"","","","","7235 WEST CHESTER PIKE","","UPPER DARBY","PA","19082","","6106220269",4245.0100,650.0000,.0000
I want to replace every double quote in multiple partial strings similar to this "UPPER DARBY FIREFIGHTERS "PAC""across the whole file.
So the result should be as below for each instance of the recurring double quotes:
"2009217",2015,3,"N","N","2","UPPER DARBY FIREFIGHTERS PAC","","","","7235 WEST CHESTER PIKE","","UPPER DARBY","PA","19082","","6106220269",4245.0100,650.0000,.0000
I came to this sed line:
cat file.txt | sed "s/\([^,]*,[^,]*,[^,]*,[^,]*,[^,]*,[^,]*,\)\([^,]*\),\(.*\)/\1\2\3/"
But now I don't know how to replace the double quote within \2.
Is that possible with sed?

Answer 1

I would personally use awk for that because it is more readable:
#!/usr/bin/env awk
BEGIN {
# Use ',' as the input and output field delimiter
FS=OFS=","
}
{
# Iterate through all fields. (NF is the number of fields.)
for(i=1;i<=NF;i++) {
# If the field starts and ends with a '"'
if($i ~ /^".*"$/) {
# Replace all '""
gsub(/"/,"",$i)
# Wrap in '"' again
$i = "\"" $i "\""
}
}
}
print

Answer 2

This might work for you (GNU sed):
sed -r ':a;s/^((([^",]*,)*("[^",]*",([^",]*,)*)*)"[^",]*)"([^,])/\1\6/;ta' file
This removes extra double quotes from strings surrounded by double quotes and delimited by ,'s.
It does this by eliminating properly constructed double quotes strings and non-quoted strings (in this example numbers) and then removes double quotes that are not followed by ,
[^",]*, # non double quoted strings
"[^",]*", # properly quoted strings
(([^",]*,)*("[^",]*",([^",]*,)*)*) # eliminate all properly constructed strings
"[^",]*"([^,]) # improper double quotes
^
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