Use the block form of grep and separate your regexes:

my $matches = grep {/1=$TAB_1/ && /5=$TAB_5/} @contents ;
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Also, the question is, are those variables supposed to be literal strings? If so, then you need to use quotemeta or \Q..\E to escape regular expression special characters:

my $matches = grep {/1=\Q$TAB_1\E/ && /5=\Q$TAB_5\E/} @contents ;
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And finally, if those strings are supposed to match in a particular order, then just put them back in a single regex with .* between them, not &&:

my $matches = grep {/1=\Q$TAB_1\E.*5=\Q$TAB_5\E/} @contents ;
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