Regular expression - SQL manipulation

[pol@fedora data]$ lsb_release -a LSB Version: :core-4.1-amd64:core-4.1-noarch Distributor ID: Fedora Description: Fedora release 34 (Thirty Four) Release: 34 Codename: ThirtyFour I'm trying to convert a sample database file from MS SQL Server to PostgreSQL. So, I'm having two small niggles that I can't resolve. shipname NVARCHAR(40) NOT NULL, That's - (**always**) two spaces - identifier (i.e. field name) - always [a-z] - lower case alphabetical - followed by an unknown number of spaces - followed by NVARCHAR(xy) NOT NULL **or** it may be followed by NVARCHAR(xy) NULL and I want to transform this into shipname TEXT NOT NULL CHECK (LENGTH(shipname) <= xy), or shipname TEXT NULL, What I have so far: sed 's/^ [a-z]+[ ]+NVARCHAR([0-9]+) NOT NULL/TEXT NOT NULL CHECK \(LENGTH\((\1) <= (\2)\)/g' So, - ^ is the beginning of the string - followed by two spaces - followed by my field name [a-z]+ - followed by an arbitrary no. of spaces [ ]+ - NVARCHAR([0-9]+) and substitute in TEXT followed by NOT NULL then CHECK(LENGTH(xy) - back reference 1 - <= back reference 2... I've tried various permutations and combinations of the above, but nothing appears to work for me. [pol@fedora data]$ sed 's/^ [a-z]+[ ]+NVARCHAR([0-9]+) NOT NULL/TEXT NOT NULL CHECK \(LENGTH\((\1) <= (\2)\)/g' sed: -e expression #1, char 87: invalid reference \2 on `s' command's RHS Get invalid back reference... **Ideally**, and I stress **ideally**, if the string following NVARCHAR(xy) is NULL and **not** NOT NULL, I don't want any length check - because it doesn't make sense to take the LENGTH of a NULL... this is conditional behaviour - not sure if it's possible in regexps.... p.s. thought this would be trivial. Have data like this: N'Strada Provinciale 1234', N'Reggio Emilia', NULL, N'10289', N'Italy'); I want to change the N' into just plain apostrophe ' (the N' is a SQL Server thing) but I don't want to change the NULL into the empty string, or worse ULL - so I tried: [pol@fedora data]$ sed 's/N\'\'/g TSQLV5.sql but get sed: -e expression #1, char 7: unterminated `s' command I know that I've used sed a lot, but would be open to any awk commands that could perform the tasks required.