$unshift(<variable name> <word list>)

• If the <variable name> argument is omitted the empty string is returned.
• If the <word list> argument is omitted the rvalue of $<variable name> is returned.
• If the value of $<variable name> is the empty string, then the value of $<variable name> is set to <word list>.
• If the value of $<variable name> is not the empty string, then the value of $<variable name> is set to <word list> plus a space plus the old value of $<variable name>.
• The new value of $<variable name> is returned.
• <variable name> must not be prefixed with a $.

Whereas the “shift” operation removes the first word from a word list (or variable), the “unshift” operation prepends words to the beginning of a word list in a variable and assigns the result back to the variable.

The new value of $<variable name> after the unshift.

assign -foo
$unshift(foo blah)      assigns "blah" to $foo and returns "blah"
$unshift(foo booya)     prepends "booya " to $foo and returns "booya blah"