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<input>
<tr><tc>1</tc><tc>2</tc><tc>3</tc></tr>
<tr><tc colspan="2">1and2</tc><tc>3</tc></tr>
<tr><tc>1</tc><tc colspan="2">2and3</tc></tr>
<tr><tc>1</tc><tc>2</tc><tc>3</tc></tr>

<RequiredOutput>
<tr><tc cNum="1">1</tc><tc cNum="2">2</tc><tc cNum="3">3</tc></tr>
<tr><tc cNum="1" colspan="2">1and2</tc><tc cNum="3">3</tc></tr>
<tr><tc cNum="1">1</tc><tc cNum="2" colspan="2">2and3</tc></tr>
<tr><tc cNum="1">1</tc><tc cNum="2">2</tc><tc cNum="3">3</tc></tr>

#!/usr/bin/perl
open(IN, "<data.in") or die ("inFile not found -- $!\n");
...

close(IN);
close(OUT);