The IFS mystery

The IFS is involved in the parsing of the command line (word splitting) and in variable assignment during the read built-in execution.

But there is a side effect, which I have only discovered recently, by accident. If you assign positional parameters with set:

$ set a 'b c' d 'e f'

than using the * parameter we can get at the values individually or as one word. To illustrate, try the following:

$ echo $* "$*"

a b c d e f a b c d e f


However, if you 'nullify' the IFS variable:

$ IFS=""

then the behaviour of the shell when referencing the * parameter changes:

$ echo $* "$*"

a b c d e f ab cde f

This only works with the * parameter (not with @) and only if IFS had a null value (if you inset IFS altogether, then the shell will use a space to separate positional parameters.

Finally, I've checked this behaviour in ksh and bash - same (and documented in manual pages, at least in bash).