Re^3: Reassign STDOUT/STDERR contents to a variable

AHA! I just ran into the same problem in some code I'm writing: I had assigned to the "in memory" variable after opening it. Turns out you can only concatenate to it, otherwise you have to seek to the beginning. Some examples:

# Save old STDIN and STDOUT
open my $oldin, '<&', \*STDIN or die "Can't dup STDIN:$!";
open my $oldout, '>&', \*STDOUT or die "Can't dup STDOUT:$!";

# set up new STDIN
my $invar = "foo\n";
close STDIN;
open STDIN, '<', \$invar or die "Can't open scalar:$!";

# set up new STDOUT
my $outvar;
close STDOUT;
open STDOUT, '>', \$outvar or die "Can't open scalar:$!";

# Try it out!
print <>;
print STDERR $out; # prints "foo"

# But beware:
# $invar = "bar\n"; #BAD! try this instead:
$invar .= "bar\n";
print STDERR <>; #Would have given your manpage. Now works!
# This might work, too, but I'm not sure:
$invar = "baz\n";
seek STDIN, 0, 0;
print STDERR <>; #Not tested, should print "baz\n";

# Another caveat about STDOUT:
$outvar = ""; #This does not do what you think.
print "ding\n";
print STDERR $outvar; #prints same as "foo\nding\n"
# instead, do this:
seek STDOUT, 0, 0;
print "dong\n";
print STDERR $outvar; # this does print "dong\n" only.

# Now restore old filehandles:
close STDIN;
open STDIN, '<&', $oldin or die "Can't redup STDIN\n";
close $oldin;
close STDOUT;
open STDOUT, '<&', $oldout or die "Can't redup STDOUT\n";
close $oldout;
[download]

UPDATE: the seek on STDIN works just fine. I decided to go that route because it scales better (always concatenating to my input scalar would keep increasing my memory usage.

print pack("A25",pack("V*",map{1919242272+$_}(34481450,-49737472,6228,0,-285028276,6979,-1380265972)))

Comment on Re^3: Reassign STDOUT/STDERR contents to a variable Select or Download Code

Replies are listed 'Best First'.
Re^4: Reassign STDOUT/STDERR contents to a variable by lothos (Novice) on Sep 25, 2009 at 22:57 UTC
Good stuff. Doesn't seem to work for my eval though.. print "Script content: $script_content\n"; print "Script input: $script_input\n"; open(SAVEOUT, ">&STDOUT"); open(SAVEERR, ">&STDERR"); close(STDIN); open(STDIN, '<',\my $stdin); #seek STDIN,0,0; # with or without, no diff. $stdin .= $script_input; #seek STDIN,0,0; # with or without, no diff. close(STDOUT); open(STDOUT,'>' , \my $stdout); close(STDERR); open(STDERR,'>' , \my $stderr); select(STDERR); $\| = 1; select(STDOUT); $\| = 1; eval $script_content; my $result_code = $@; close(STDOUT); close(STDERR); open(STDOUT, ">&SAVEOUT"); open(STDERR, ">&SAVEERR"); if ( ! $stderr ) { $stderr = ''; } # my db doesn't like nulls. if ( ! $stdout ) { $stdout = ''; } print "STDERR:" . $stderr; print "STDOUT:" . $stdout; [download] In all variations where I'm using STDIN that is tied to a variable, I still get the manpage. Argh. I'm thinking the difference is that in your scenario you can do your writes to STDIN after the process has it. I think I have to have it set up prior to my eval, or my read of stdin within my evaled script will just return as it would get EOF immediately.	[reply] [d/l]

Replies are listed 'Best First'.

Re^4: Reassign STDOUT/STDERR contents to a variable
by lothos (Novice) on Sep 25, 2009 at 22:57 UTC

Good stuff. Doesn't seem to work for my eval though..

print "Script content: $script_content\n";
print "Script input: $script_input\n";
open(SAVEOUT, ">&STDOUT");
open(SAVEERR, ">&STDERR");
close(STDIN);
open(STDIN, '<',\my $stdin);
#seek STDIN,0,0; # with or without, no diff.
$stdin .= $script_input;
#seek STDIN,0,0; # with or without, no diff.
close(STDOUT);
open(STDOUT,'>' , \my $stdout);
close(STDERR);
open(STDERR,'>' , \my $stderr);
select(STDERR); $| = 1;
select(STDOUT); $| = 1;
eval $script_content;
my $result_code = $@;
close(STDOUT);
close(STDERR);
open(STDOUT, ">&SAVEOUT");
open(STDERR, ">&SAVEERR");
if ( ! $stderr ) { $stderr = ''; } # my db doesn't like nulls.
if ( ! $stdout ) { $stdout = ''; }
print "STDERR:" . $stderr;
print "STDOUT:" . $stdout;
[download]

In all variations where I'm using STDIN that is tied to a variable, I still get the manpage. Argh.

I'm thinking the difference is that in your scenario you can do your writes to STDIN after the process has it. I think I have to have it set up prior to my eval, or my read of stdin within my evaled script will just return as it would get EOF immediately.

[reply]
[d/l]