Re^2: How can you sysread an entire file?

[davidrw]

Is push(@array, $_) while <DF>; really that much slower?

Why not just @array = <DF> or push @array, <DF> ?
Hmm.. as i was about to hit 'Create' i think i answered my own question -- those two make a copy of the whole <DF> array first, right? where your push/while avoids it ...


Also, to OP's first part, you can use Perl Idioms Explained - my $string = do { local $/; <FILEHANDLE> }; to slurp the whole file ...

[NeilF]

Unfortunately I don't think I can use that "idioms" as I really do need to use sysread... (Due to IO operations being counted by ISP.)

[ikegami]

my $string = do { local $/; <FILEHANDLE> };
looks nicer than
my $string; { local $/; $string = <FILEHANDLE> }
but takes twice as much memory. That's probably not that wise when dealing with entire files.

[BrowserUk]

I think I made an interesting discovery. As you suggest above, if I do this it only makes one copy of the file in memory:

P:\test>perl -le"
my $s; do{ local $/; $s=<>}; 
print length $s; 
system qq[tasklist /fi \"pid eq $$\" ]" 1000000.dat

11000001

Image Name                   PID Session Name     Session#    Mem Usag
+e
========================= ====== ================ ======== ===========
+=
perl.exe                     604                         0     12,860 
+K

And if I do it this way it uses two copies:

P:\test>perl -le"
my $s=do{ local $/; <>}; 
print length $s; 
system qq[tasklist /fi \"pid eq $$\" ]" 1000000.dat

11000001

Image Name                   PID Session Name     Session#    Mem Usag
+e
========================= ====== ================ ======== ===========
+=
perl.exe                    1372                         0     23,624 
+K

But what fooled me, as I was using my perl shell, is that if you eval the statement, only one copy is made:

P:\test>perl -le"
my $s = eval q[do{ local $/; <>}]; 
print length $s; 
system qq[tasklist /fi \"pid eq $$\" ]" 1000000.dat

11000001

Image Name                   PID Session Name     Session#    Mem Usag
+e
========================= ====== ================ ======== ===========
+=
perl.exe                    1764                         0     12,880 
+K

And I can't quite figure out why that should be so?

[BrowserUk]

takes twice as much memory.

Do you have some evidence of that as it appears to make no difference at all on my system?

Update: I take that back. It does double the memory usage.