Not so. Unlike read (which waits for all 4096 characters to be read in) and <FILE> (which waits for a whole line to be read in), sysread returns as soon as possible. For example, 
perl -e "$|=1; print 'test1'; sleep 1; print 'test2'" | perl -e "sysre
+ad(STDIN, $buf='', 1000); print(qq{[$buf]})"

[download]

outputs 

[test1]

[download]

If what you claimed is true, it would output [test1test2].

( And I'm working on the caveat. And I've addressed the caveat in an update. )

In reply to Re^5: Filtering passwords from the output of a script by ikegami
in thread Filtering passwords from the output of a script by quester

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