i have file containing lines such as

Char(Month(L.prd_cvrg_end_dt)) =
STRIP(substr(V_MON_YR,1,2),L,'0')
AND Char(Year(L.prd_cvrg_end_dt))

which i need to change as:

Char(Month(L.prd_cvrg_end_dt)) =
STRIP(substr(V_MON_YR,1,2),'L','0')
AND Char(Year(L.prd_cvrg_end_dt))

how do i get this done.

i.e. change only the character ,L, to ,'L',

i attempted using sed/awk it looks like i have an error.

the single quote didn't make the changes.

tried double quote(") instead of single quote('), it works

cat t1 | sed -e "s/,L,/,'L',/g" > t2

yeah single quote will cause an error
i.e.
cat in-file | sed -e 's/,L,/,'
then L
then ',/g' > out-file

I'm not 100% on sed but i would imagine you could delimit that to give you :
cat in-file | sed -e 's/,L,/,\'L\',/g' > out-file

Right. Escaping the nested single quotes will work. This is not an sed thing but rather the shell takes care of the escaping.

...and why exactly do you need a 'cat'?