How do I replace certain text with the respective line number using sed?

Question

I have a file where certain (not all) lines look like so:

Sequence: n

I wish to replace n with the respective line number.

How can I do it with sed?

By "do it with sed" do you mean "do it with sed" or "do it with any common tool"? Because people say the former and mean the latter about 98% of the time

enzotib · Answer 1 · 2011-08-26 07:35:13Z

up vote 4 down vote

It is very simple with awk (thanks to @glenn jackman):

awk '/Sequence: n/ { $2 = NR } { print }' input-file

Regarding sed, I've only been able to do this with a two-pass elaboration (tested with GNU sed and with ssed:):

sed '/^Sequence: n$/{s/n$//p;=;d;}' | sed '/^Sequence: $/{N;s/\n//;}'

The first inserts the line number in the row after "Sequence: ", the second joins the two lines.

edited Aug 26 '11 at 7:35

answered Aug 25 '11 at 16:42

enzotib
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2

I'd write your awk command as: awk '/Sequence: n/ {$2 = NR} {print}' – glenn jackman Aug 25 '11 at 21:22

@glenn jackman: well done, my bad. – enzotib Aug 26 '11 at 7:22

1 Answer