Dear Monks, I have to build a substitution regexp, but this case is too hard for me.
We have a data:
 
1stline....pattern1.......pattern1.....
2ndline....pattern1.....pattern2...pattern1...
1a line....pattern1.......pattern1.....
2a line....pattern1........pattern2...pattern1.....

[download]
"\n" and "." doesn't matter (so I can't split it into many lines and process separately). line numbers just for reference, and real data may mix 1st and 2nd type of lines in random way.

what we must get: 
 
1stline....pattern1.......pattern1.....
2ndline....subst...
1a line....pattern1.......pattern1.....
2a line....subst.....

[download]
I realize I should do it with
s/pattern1(not-pattern1)*?pattern2(not-pattern1)*?pattern1/subst/isg
but hung.
What I already tried:

pattern1([^p][^a][^t]...[^1])*?pattern2([^p][^a][^t]...[^1])*?pattern1
pattern1.(pattern1){0}*?pattern2.(pattern1){0}*?pattern1

[download]
and so on.
Of couse tried:
O'Reilly Perl bookshelf
man perlretut
Also I tried to search, but (probably because of my English) I didn't find anything helpful.

perl, v5.8.6, Linux.

Please, help. Thank you very much.

In reply to How can I build regexp with "not" assertion? by putnik

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