shift.1 - nroff source : Read shift(I) in pdf, ps, or txt form.
shift - adjust Shell arguments
Shift is used in Shell command files to shift the argument list left by
1, so that old $2 can now be referred to by $1 and so forth. Shift is
useful to iterate over several arguments to a command file. For exam-
ple, the command file
if $1x = x exit
pr -3 $1
prints each of its arguments in 3-column format.
Shift is executed within the Shell.