I am afraid this: 
perl -anle"next unless @L; print if $L[0] eq $F[0]; @L = @F;" in.txt >
+ out.txt

[download]
will never enter into the loop because the next statement at the beginning will prevent @L from ever being set.

Perhaps this instead: 

perl -anwle 'BEGIN{$L = "";}  print if $F[0] eq $L; $L = $F[0];' in.tx
+t > out.txt

[download]
Although the BEGIN block isn't really necessary if the warnings are not activated: 
perl -anle 'print if $F[0] eq $L; $L = $F[0];' in.txt > out.txt

[download]

In reply to Re^2: how to change this code into perl by Laurent_R
in thread how to change this code into perl by perlnewbie012215

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