perl -Mre=debug -E" $_=q{foo/src/com/stuff/ggbargg.java}; m/(?<!fee).*[Bb]ar.*\.java/ "

 perl -Mre=debug -E" $_=q{foo/src/com/stuff/ggbargg.java}; m{(?<!fee)/.*[Bb]ar.*\.java} "

 perl -Mre=debug -E" $_=q{foo/src/com/stuff/ggbargg.java}; m{^(?<!fee)/.*[Bb]ar.*\.java} "

 perl -Mre=debug -E" $_=q{foo/src/com/stuff/ggbargg.java}; !/fee/ and /[Bb]ar.*\.java$/ "

Just use two regexen:

#! perl
use strict;
use warnings;

while (my $line = <DATA>)
{
    chomp  $line;
    print "$line\n" if $line =~ / [Bb]ar .* \. java $ /x &&
                       $line !~ / ^ fee /x;
}

__DATA__
foo/src/com/stuff/xxxxxx.java
foo/src/com/stuff/ggbargg.java
foo/src/com/stuff/ggBargg.java
fee/src/com/stuff/ggbargg.java
fee/src/com/stuff/ggBargg.java
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Output:

22:32 >perl 531_SoPW.pl
foo/src/com/stuff/ggbargg.java
foo/src/com/stuff/ggBargg.java

22:37 >
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Hope that helps,

Update: No need for $line:

while (<DATA>)
{
    chomp;
    print "$_\n" if / [Bb]ar .* \. java $ /x && !/ ^ fee /x;
}
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You don't have fixed width of line, look behind or look ahead will only work on fixed width

use strict;
use warnings;

while(my $line = <DATA>)
{
    chomp($line);
    if( $line =~ /(?<!fee\/src\/)(com\/)/ )
    {
        print $line . "\n";
    }
}
__DATA__
foo/src/com/
foo/src/com/
foo/src/com/
fee/src/com/
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Sorry, but that's half wrong. See perldoc perlretut which makes it very clear: look aheads need NOT be fixed width; only the look behind flavor.

If you didn't program your executable by toggling in binary, it wasn't really programming!

I would say only Athanasius has a correct answer yet, I see mistakes in the other answers. So I made sure and tested. This should work (and still uses only one regex):

if( $line =~ /^(?!fee).*[Bb]ar.*\.java/ )
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This is a negative look-ahead fixed at the start of the line (with ^).

I would say only Athanasius has a correct answer yet, I see mistakes in the other answers.

obviously wrong

If you mean to say your fourth answer is correct I beg to differ. !/fee/ aborts for "fee" anywhere in the string instead of only at the start like the OP wanted

UPDATE:

If you mean to say your third answer is correct I beg to differ. It expects a '/' after "fee". While this is always the case in the examples it is not what the OP said (although there is a chance that the OP misstated the problem)

I wanted a single regexp if possible and this looks like it does the trick. Many thanks for the replies !

G'day SirClive,

Another method is to simply skip lines starting with fee then test for [Bb]ar:

$ perl -Mstrict -Mwarnings -E '
    my @data = qw{
        foo/src/com/stuff/xxxxxx.java
        foo/src/com/stuff/ggbargg.java
        foo/src/com/stuff/ggBargg.java
        fee/src/com/stuff/ggbargg.java
        fee/src/com/stuff/ggBargg.java
    };
    for (@data) {
        next if /^fee/;
        say if /[Bb]ar/;
    }
'
foo/src/com/stuff/ggbargg.java
foo/src/com/stuff/ggBargg.java
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