Yes, you're right about the unnecessary newlines. I fixed the newline where it feeds the file one line at a time to the child. The perl absolutely reaches "END".

test.js is three simple lines: 

var foo=0;
var bar=1;
var baz=2;

[download]

And I can type these in, one at a time, into the running javascript program from the command line: 

$ js
js> load('jslint.js');
var foo=0;
var bar=1;
var baz=3;
END
jslint: No problems found.

$

[download]

If I drop warns in: 

open FILE, '<', "test.js";
while (<FILE>)
{
    warn "printing $_";
    print $JSWRITE "$_";
}
close(FILE);

warn "printing END\n";
print $JSWRITE "END\n";

[download]

I see: 

$ ./jslint.pl 
printing var foo=0;
printing var bar=1;
printing var baz=3;
printing END

[download]

And strace shows this: 

...
write(4, "load(\'jslint.js\');\n", 19)  = 19
open("test.js", O_RDONLY)               = 3
ioctl(3, SNDCTL_TMR_TIMEBASE or TCGETS, 0x7fff8d5e9440) = -1 ENOTTY (I
+nappropriate ioctl for device)
lseek(3, 0, SEEK_CUR)                   = 0
fstat(3, {st_mode=S_IFREG|0664, st_size=33, ...}) = 0
fcntl(3, F_SETFD, FD_CLOEXEC)           = 0
read(3, "var foo=0;\nvar bar=1;\nvar baz=3;"..., 4096) = 33
write(2, "printing var foo=0;\n", 20printing var foo=0;
)   = 20
write(4, "var foo=0;\n", 11)            = 11
write(2, "printing var bar=1;\n", 20printing var bar=1;
)   = 20
write(4, "var bar=1;\n", 11)            = 11
write(2, "printing var baz=3;\n", 20printing var baz=3;
)   = 20
write(4, "var baz=3;\n", 11)            = 11
read(3, "", 4096)                       = 0
close(3)                                = 0
write(2, "printing END\n", 13printing END
)          = 13
write(4, "END\n", 4)                    = 4
close(4)                                = 0
read(5,  <unfinished ...>

[download]

Which, if I remove reading from $JSREAD, becomes: 

write(4, "load(\'jslint.js\');\n", 19)  = 19
open("test.js", O_RDONLY)               = 3
ioctl(3, SNDCTL_TMR_TIMEBASE or TCGETS, 0x7fff38afb950) = -1 ENOTTY (I
+nappropriate ioctl for device)
lseek(3, 0, SEEK_CUR)                   = 0
fstat(3, {st_mode=S_IFREG|0664, st_size=33, ...}) = 0
fcntl(3, F_SETFD, FD_CLOEXEC)           = 0
read(3, "var foo=0;\nvar bar=1;\nvar baz=3;"..., 4096) = 33
write(2, "printing var foo=0;\n", 20printing var foo=0;
)   = 20
write(4, "var foo=0;\n", 11)            = 11
write(2, "printing var bar=1;\n", 20printing var bar=1;
)   = 20
write(4, "var bar=1;\n", 11)            = 11
write(2, "printing var baz=3;\n", 20printing var baz=3;
)   = 20
write(4, "var baz=3;\n", 11)            = 11
read(3, "", 4096)                       = 0
close(3)                                = 0
write(2, "printing END\n", 13printing END
)          = 13
write(4, "END\n", 4)                    = 4
close(4)                                = 0
close(5)                                = 0
wait4(8790,  <unfinished ...>

[download]

In reply to Re^4: Diagnosing blocking io (or: finding the WHY of my Open2 woes). by Socrates
in thread Diagnosing blocking io (or: finding the WHY of my Open2 woes). by Socrates

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