Paul comment on Famous Awk One-Liners Explained, Part III: Selective Printing and Deleting of Certain Lines

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Perl one-liners explained

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Paul Permalink

July 29, 2009, 16:46

Serious error in #45, #46 and many others.
FNR is the line number in the *current* file.
NR is the cumulative line number across all inputs.

awk 'code' six_lines.txt ten_lines.txt will have
NR == 1 and FNR == 1
NR == 7 and FNR == 1 again
and END will see NR == 16 and FNR == 10.

Programs that check for change in FILENAME would be more efficient to check for FNR == 1.

Awk to print first 10 lines of several files:

awk 'FNR == 1 { print "\n.... " FILENAME; } FNR < 11

If your awk has "nextfile" it saves reading lines after first 10.

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Famous Awk One-Liners Explained, Part III: Selective Printing and Deleting of Certain Lines