I've tested your code with this input : 
 
my @in = (
        'S_FER_SCAM1_ARRESTO;ARRESTO;ST;0;ST;1;0;TS;0;0',
    'S_VINREU_RLIP1_ALLARMEZONA3;ALLARME ZONA  3;SU LI IR ST;0;SU LI I
+R ST;1;0;TS;0;0',
    'S_VINREU_RLIP1_ANOMBAT;ANOMALIA BATTERIA;SU LI IR ST;0;SU LI IR S
+T;1;0;TS;0;0',
    'S_FER_VENT1_ERRCOLINV;ERRORE PROFIBUS COLL INVERTER;SU LI IR ST;0
+;SU LI IR ST;1;0;TS;0;0',
    'S_VINREU_RLIP1_CIRCZONE1;CIRCUITO ZONA 1 FUNZONANTE;SU LI IR ST;0
+;SU LI IR ST;1;0;TS;0;0',
    'S_VINREU_RLIP1_CIRCZONE2;CIRCUITO ZONA 2 FUNZONANTE;SU LI IR ST;0
+;SU LI IR ST;1;0;TS;0;0',
        'S_FER_SCAM1_ARRESTO;ARRESTO;SU LI IR ST;0;SU LI IR ST;1;0;TS;
+0;0',
    'S_FER_VENT1_ERRCOLINV;ERRORE PROFIBUS COLL INVERTER;ST;0;ST;1;0;T
+S;0;0'
);

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I print  @have array and it shows 7 lines with  S_FER_VENT1_ERRCOLINV is duplicated (should show only 6), it hide only one, in my data file I've lines that have the same id ($1) two times and others are normal (no duplicate id)

In reply to Re^4: How to check lines that start with the same word then delete one of them by agnes00
in thread How to check lines that start with the same word then delete one of them by agnes00

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