perl file test operators and "$_" -

i'm going through o'reilly's "intermediate perl". -s used so:

print map { "    $_\n" } grep { -s < 1000 } @argv; 

which gives warning:

warning: use of "-s" without parentheses ambiguous unterminated <> operator

though, when put parentheses around -s works charm. not sure if perl version related or mistype authors.

perl version: v5.18.2 built darwin-thread-multi-2level

what causing issue , can correct it?

< can start of term readline/glob shortcut.

print "[$_]\n" < b c >; 

< can start of infix operator numeric less-than operator.

print "foo\n" if $x < 3; 

-s can legally followed both, perl has guess 1 wanted when sees <. using of following instead of -s solves issue since none of them can followed term:

• -s($_)
• -s()
• (-s)