awk if-then-else statement error - if-statement

Question

I am writing an if-then-else statement using awk in a bash script.
What I would like to do is identify lines with col 1 values not matching a particular string (rs or chr) and append a prefix (chr) to the col 1 values for those identified lines. All lines with the matched string should print as they were - no appending.
My line of code so far is:
awk '{if (! ($1 ~ /rs/ || $1 ~ /chr/)) {($1 == "chr"$1); print $0}}; else {print $0}' filename > newfilename
I keep on receiving syntax error messages with this code.
I can perform the identification and the appending successfully on their own but am having problems combining them into one command.

Answer 1

With idiomatic awk you can rewrite this as
awk '$1!~/rs/ && $1!~/chr/ {$1="chr"$1}1'
or if you like
awk '!($1 ~ /rs/ || $1 ~ /chr/) {$1="chr"$1}1'
or, equivalently
awk '!(/^rs/ || /^chr/) {$1="chr"$1}1'
you can avoid assignment since there is no further action other than printing with
awk '!(/^rs/ || /^chr/) {print "chr"$0;next}1'

Answer 2

sometimes, writing codes in multiple lines may help you spot the mistake:
'{
if (! ($1 ~ /rs/ || $1 ~ /chr/)) {
($1 == "chr"$1);
print $0
}
};
else {print $0}'
You will see that the else is out of the {...}
stay with your codes, this will fix the problem:
'{
if (! ($1 ~ /rs/ || $1 ~ /chr/)) {
($1 == "chr"$1);
print $0
}else
print $0
}'
for the code improvement, check karakra's answer.

Answer 3

The way to write your code syntactically correctly is:
awk '!($1 ~ /rs/ || $1 ~ /chr/) {$1="chr"$1} 1' filename > newfilename
but be warned that the assignment might change the white space in your file so what you probably really want is:
awk '!($1 ~ /rs/ || $1 ~ /chr/) {sub(/^[[:space:]]*/,"&chr")} 1' filename > newfilename