show specific lines from all files with .txt extension

Question

How can I print specific lines (say the 7th and 15th) of each file in the current directory whose name ends in .txt?

Answer 1

There are many ways. Here are a few:

• awk

  awk 'FNR==7 || FNR==15' *.txt
  

  FNR is the line number of the current file. Because the default action in awk when an expression evaluates to true is to print the current line, this will print lines 7 and 15 of each .txt file.

Awk is the only tool I know that can easily (others can do it but not quite so simply) distinguish between the line number of all input and the line number of the current file. Therefore, the other suggestions involve shell loops:

• sed

  for f in *.txt; do sed -n '7p;15p' "$f"; done
  

• Perl

  for f in *.txt; do perl -ne 'print if $.==7 or $.==15' "$f"; done
  

  Or, to avoid the shell loop:

  perl -ne '$c++; print if $c==7 or $c==15; $c=0 if eof' *.txt