How to convert MSSQL trigger to postgresql trigger

 CREATE TRIGGER Exampaperdetails_AUDIT ON Exampaperdetail FOR
BEGIN UPDATE,DELETE
AS

DECLARE v_bit INT ;
       v_field INT ;
       v_maxfield INT ;
       v_char INT ;
       v_fieldname VARCHAR(128) ;
       v_TableName VARCHAR(128) ;
       v_PKCols VARCHAR(1000) ;
       v_sql VARCHAR(2000); 
       v_UpdateDate VARCHAR(21) ;
       v_UserName VARCHAR(128) ;
       v_Type CHAR(1) ;
       v_PKSelect VARCHAR(1000)


--You will need to change @TableName to match the table to be audited. 
-- Here we made GUESTS for your example.
 v_TableName := 'EXAMPAPERDETAIL'

-- date and user
         v_UserName := SYSTEM_USER ,
       v_UpdateDate := TO_CHAR (NOW(), 112) 
               || ' ' || TO_CHAR (NOW(), 114)

-- Action
IF EXISTS (SELECT * FROM inserted) THEN
       IF EXISTS (SELECT * FROM deleted) THEN
               v_Type := 'U';
       ELSE
               v_Type := 'I';
       END IF;
ELSE
       v_Type := 'D';
END IF;

-- get list of columns
SELECT * INTO #ins FROM inserted
SELECT * INTO #del FROM deleted


-- Get primary key columns for full outer join
SELECT COALESCE(v_PKCols || ' and', ' on') 
               || ' i.' || c.COLUMN_NAME || ' = d.' || c.COLUMN_NAME INTO v_PKCols
       FROM    INFORMATION_SCHEMA.TABLE_CONSTRAINTS pk ,

              INFORMATION_SCHEMA.KEY_COLUMN_USAGE c
       WHERE   pk.TABLE_NAME = v_TableName
       AND     CONSTRAINT_TYPE = 'PRIMARY KEY'
       AND     c.TABLE_NAME = pk.TABLE_NAME
       AND     c.CONSTRAINT_NAME = pk.CONSTRAINT_NAME

-- Get primary key select for insert
SELECT COALESCE(v_PKSelect||'+','') 
       || '''<' || COLUMN_NAME 
       || '=''+convert(varchar(100),
coalesce(i.' || COLUMN_NAME ||',d.' || COLUMN_NAME || '))+''>''' INTO v_PKSelect 
       FROM    INFORMATION_SCHEMA.TABLE_CONSTRAINTS pk ,
               INFORMATION_SCHEMA.KEY_COLUMN_USAGE c
       WHERE   pk.TABLE_NAME = v_TableName
       AND     CONSTRAINT_TYPE = 'PRIMARY KEY'
       AND     c.TABLE_NAME = pk.TABLE_NAME
       AND     c.CONSTRAINT_NAME = pk.CONSTRAINT_NAME

IF v_PKCols IS NULL
THEN
       RAISERROR('no PK on table %s', 16, -1, v_TableName)
       RETURN;
END IF;

SELECT         0, 
       MAX(ORDINAL_POSITION) INTO v_field, v_maxfield 
       FROM INFORMATION_SCHEMA.COLUMNS WHERE TABLE_NAME = v_TableName
WHILE v_field < v_maxfield
LOOP
       SELECT MIN(ORDINAL_POSITION) INTO v_field 
               FROM INFORMATION_SCHEMA.COLUMNS 
               WHERE TABLE_NAME = v_TableName 
               AND ORDINAL_POSITION > v_field
       v_bit := (v_field - 1 )% 8 + 1
       v_bit := POWER(2,v_bit - 1)
       v_char := ((v_field - 1) / 8) + 1
       IF SUBSTRING(COLUMNS_UPDATED(),v_char, 1) & v_bit THEN >
       END IF; 0
                                       OR v_Type IN ('I','D')
       BEGIN
               SELECT COLUMN_NAME INTO v_fieldname 
                       FROM INFORMATION_SCHEMA.COLUMNS 
                       WHERE TABLE_NAME = v_TableName 
                       AND ORDINAL_POSITION = v_field
               v_sql := '
insert LogExamPaperMarks (RegNo, 
			   SubPaperCode,
			   ExamSession,
			   TableName,
               FieldName,
               OldValue, 
               NewValue, 
               Date,
               UserID)
select convert(varchar(100),  coalesce(i.RegNo,d.RegNo)), 
convert(varchar(100),  coalesce(i.SubPaperCode,d.SubPaperCode)),
convert(varchar(100),  coalesce(i.ExamSession,d.ExamSession)),'''
       || v_TableName || ''','''
       || v_fieldname || ''''
       || ',convert(varchar(1000),d.' || v_fieldname || ')'
       || ',convert(varchar(1000),i.' || v_fieldname || ')'
       || ',''' || v_UpdateDate || ''''
       || ',convert(varchar(100),  coalesce(i.opt1,d.opt1))'
       || ' from #ins i full outer join #del d'
       || v_PKCols
       || ' where i.' || v_fieldname || ' <> d.' || v_fieldname 
       || ' or (i.' || v_fieldname || ' is null and  d.'
                                || v_fieldname
 || ' is not null)' 
       || ' or (i.' || v_fieldname || ' is not null and  d.' 
                                || v_fieldname
                                || ' is null)' 
               EXECUTE (v_sql)
       END
END LOOP;
 

ALTER TABLE dbo.Exampaperdetail ENABLE TRIGGER Exampaperdetails_AUDIT
GO