$alloutput=`cmd 2>&1`; # This should capture both stdout and stderr.

##</code><code>##

% cat asdf
#!/bin/sh
echo "output to stdout"
echo "output to stderr" >&2

##</code><code>##

% perl -e '$x=`./asdf 2>&1`;print "Captured $x"'
Captured output to stdout
output to stderr

##</code><code>##

    $output = `cmd 2>&1`;                   # either with backticks
    $pid = open(PH, "cmd 2>&1 |");          # or with an open pipe
    while (<PH>) { }                        #    plus a read

##</code><code>##

% perl -e 'open(F,"./asdf 2>&1|");while($x=<F>){print "Captured $x";}'
Captured output to stdout
Captured output to stderr