perlbrew exec perl -wle 'print " A" x 1e0 for 1 .. 1e2' | less -S
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But if I try with slightly changed line:

perlbrew exec perl -wle 'print " A" x 1e0 for 1 .. 1e2' | less -S
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There is no warning, although I didn't scroll the whole output.

perl -wle 'print " A" x 1e0 for 1 .. 1e2' is 300 bytes, while perl -wle 'print " A" x 1e3 for 1 .. 1e2' is 200100 bytes. Since you're piping the output of perl to another program, perl's output isn't line-based (see e.g. Suffering from Buffering), and so what I'm fairly certain is happening is that perl is simply outputting the 300 bytes in one go. Update: Because perl -wle '$|++; print " A" x 1e0 for 1 .. 1e2' isn't killed by SIGPIPE either, it may also have something to do with how much data a pipe can buffer, but I'm not an expert on that.

I think Linux pipes can usually hold 128 KiB. This surely configurable.

Update:

$ perl -e'
   $|=1;
   $SIG{PIPE} = sub { die("SIGPIPE") };
   print "x" x 1..15_328;
' | sleep 0.25   # Child needs to be alive when the print occurs.

$ perl -e'
   $|=1;
   $SIG{PIPE} = sub { die("SIGPIPE") };
   print "x" x 1..15_329;
' | sleep 0.25
SIGPIPE at -e line 3.
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It's 15,328 on my Ubuntu (over WSL2) system. What a weird number. That's 1,056 bytes less than 16 KiB (16,384).

Seeking work! You can reach me at ikegami@adaelis.com