for such conversions you can use a2p

> echo '/user@example.com/ {print $2}' |a2p 
#!/usr/bin/perl
eval 'exec /usr/bin/perl -S $0 ${1+"$@"}'
    if $running_under_some_shell;
            # this emulates #! processing on NIH machines.
            # (remove #! line above if indigestible)
 
eval '$'.$1.'$2;' while $ARGV[0] =~ /^([A-Za-z_0-9]+=)(.*)/ && shift;
            # process any FOO=bar switches
 
$, = ' ';        # set output field separator
$\ = "\n";        # set output record separator
 
while (<>) {
    ($Fld1,$Fld2) = split(' ', $_, -1);
    if (/user@example.com/) {
    print $Fld2;
    }
}
[download]

anyway you're not checking the first column but the whole line for an email address.

consider prepending an ^ in your regex.

UPDATE: IMHO the @ in the regex should be escaped to avoid array interpolation, seems to be a bug in a2p.