Use of IFS in "for loop"

Question

lis="a:b:c:d:"
IFS=:

If I run the following code,

for i in "a:b:c:d:";
do 
 echo the output is $i
done

I get:

the output is a b c d

If I replace "a:b:c:d:" with $lis instead:

for i in $lis;
do 
 echo the output is $i
done

I have the expected output:

the output is a
the output is b
the output is c
the output is d

I wonder what is wrong, $lis is basically the same as "a:b:c:d"

• muru: Possible duplicate of When is double-quoting necessary?
• muru: '$lis is basically the same as "a:b:c:d"' ... "$lis" might be, but $lis isn't.

Answer 1

The big difference is where word splitting is performed. Double quotes ensure that a literal string or quoted variable like "$lis" would be treated as single item

for i in "a:b:c:d:";
do 
 echo the output is $i
done

Therefore in this loop the double quoted "a:b:c:d:" is a single item, hence why you see only one line of output

the output is a b c d

---

for i in $lis;
do 
 echo the output is $i
done

Here the $lis is unquoted, hence the shell will perform word splitting according to the IFS value you've set. The shell will see there's 4 items provided to the for loop. Hence why you see four lines of output.

If you double quote "$lis" variable, the word splitting won't be performed, hence you should see identical output - only one line - to the first case.

• Mehdi Charife: How can you set IFS only within the scope of the for block?
• David Ongaro: a:b:c:d: is a literal, regardless if quotes are used or not. So in this case, the issue doesn't have anything to do with the quotes, but rather with the fact word splitting doesn't apply to literals.