What's the difference between $@ and $* in UNIX?

Question

What\'s the difference between $@ and $* in UNIX? When echoed in a script, they both seem to produce the same output.

Answer 1

One difference is in how they handle the IFS variable on output.

#!/bin/sh
echo "unquoted asterisk " $*
echo "quoted asterisk $*"
echo "unquoted at " $@
echo "quoted at $@"
IFS="X"
echo "IFS is now $IFS"
echo "unquoted asterisk " $*
echo "quoted asterisk $*"
echo "unquoted at " $@
echo "quoted at $@"

If you run this like this: ./demo abc def ghi, you get this output:

unquoted asterisk abc def ghi
quoted asterisk abc def ghi
unquoted at abc def ghi
quoted at abc def ghi
IFS is now X
unquoted asterisk abc def ghi
quoted asterisk abcXdefXghi
unquoted at abc def ghi
quoted at abc def ghi

Notice that (only) the "quoted asterisk" line shows an X between each "word" after IFS is changed to "X". If the value of IFS contains multiple characters, only the first character is used for this purpose.

This feature can also be used for other arrays:

$ array=(123 456 789)
$ saveIFS=$IFS; IFS="|"
$ echo "${array[*]}"
123|456|789
$ IFS=$saveIFS