How does `IFS` affect `*` expansion?

When you use the * expansion (specifically inside double quotes: "${NAMES[*]}"), Bash merges all array elements into a single string.

The IFS (Internal Field Separator) variable determines which character is used to join those elements together. By default, IFS contains a space, a tab, and a newline. Bash uses the first character of IFS as the separator.

How it works in practice

Let's look at an example in the terminal:

# Define an array
NAMES=("John" "Eric" "Jessica")

# Scenario 1: Default IFS (Space)
echo "${NAMES[*]}" 
# Output: John Eric Jessica

# Scenario 2: Change IFS to a comma
IFS=","
echo "${NAMES[*]}" 
# Output: John,Eric,Jessica

# Scenario 3: Change IFS to a colon
IFS=":"
echo "${NAMES[*]}" 
# Output: John:Eric:Jessica

Why this is useful

This is a "secret weapon" for quickly generating CSV (Comma Separated Values) or paths without writing a loop. If you have an array and you need to turn it into a comma-separated list for a report or a command, you just temporarily change IFS.

The "Clean" Way to use it

If you change IFS in a script, it affects everything else in that script too (which can cause bugs!). It is best practice to save the old IFS and restore it:

OLD_IFS=$IFS        # Save the original
IFS="|"             # Set your custom separator
MY_STRING="${NAMES[*]}"
IFS=$OLD_IFS        # Restore the original

Contrast with @

The IFS variable does not affect "${NAMES[@]}".
The @ expansion always keeps elements separate, regardless of what IFS is set to. This is why @ is considered "safe" and * is considered "special purpose."

In summary: IFS acts as the "glue" character when you tell Bash to "squash" an array into a single string using *.