If you want to output a string consisting of the elements of an array delimited by a particular character, then use

words=(a b c)

( IFS=,; printf '%s\n' "${words[*]}" )

Using * in place of @ in "${words[*]}" will create a single string out of the concatenation of all elements of the array words. The elements will be delimited by the first character of $IFS, which is why we set this to a comma before doing the expansion.

I set IFS in a subshell to avoid inadvertently setting it for any other operation than the single expansion needed to create the comma-delimited string for the printf call.

If you want to output a string consisting of the elements of an array delimited by a particular character, then use

words=(a b c)

( IFS=,; printf '%s\n' "${words[*]}" )

Using * in place of @ in "${words[*]}" will create a single string out of the concatenation of all elements of the array words. The elements will be delimited by the first character of $IFS, which is why we set this to a comma before doing the expansion.

I set IFS in a subshell to avoid inadvertently setting it for any other operation than the single expansion needed to create the comma-delimited string for the printf call.

Instead of using a subshell to set IFS locally, you may instead set it and then reset it:

words=(a b c)

IFS=,$IFS
printf '%s\n' "${words[*]}"
IFS=${IFS#?}

This first adds a comma as the first character of $IFS, retaining the old value of the variable as the characters after the comma.

The parameter substitution ${IFS#?} would delete the first character (the comma that we added).

If you want to output a string consisting of the elements of an array delimited by a particular character, then use

words=(a b c)

( IFS=,; printf '%s\n' "${words[*]}" )

Using * in place of @ in "${words[*]}" will create a single string out of the concatenation of all elements of the array words. The elements will be delimited by the first character of $IFS, which is why we set this to a comma before doing the expansion.

I set IFS in a subshell to avoid setting it for any other operation than the expansion needed for the printf call.

If you want to output a string consisting of the elements of an array delimited by a particular character, then use

words=(a b c)

( IFS=,; printf '%s\n' "${words[*]}" )

Using * in place of @ in "${words[*]}" will create a single string out of the concatenation of all elements of the array words. The elements will be delimited by the first character of $IFS, which is why we set this to a comma before doing the expansion.

I set IFS in a subshell to avoid inadvertently setting it for any other operation than the single expansion needed to create the comma-delimited string for the printf call.