Insert at the beginning of odd lines

Shell Programming and Scripting
1

Hello people,

I am trying with sed to insert some text at the beginning of each odd line of a file but no luck. Can you please help. Awk is also suitable but I am not very familiar with it.

Thank you in advance for any help.

2

What have you tried with sed?

3

Read in two lines at once with the "N" subcommand, then insert after the "\n", which is the newline separating the lines:

sed 'N;s/\n/&=changes here=/p'

In case of files with uneven numbers of lines you will have to introduce a special rule for the last line ("$"), otherwise the last line will not be printed.

I hope this helps.

bakunin

4

Something simpler and what you require:

cat testfile
ABCD
EFGH
IJKL
MNOP
PQRS

sed 's/.*/NEW TEXT &/;n' testfile
NEW TEXT ABCD
EFGH
NEW TEXT IJKL
MNOP
NEW TEXT PQRS
1 Like
5

with awk..:slight_smile:

awk 'NR%2{$0="some text "$0}1' file
1 Like
6

Another sed variation - if you have GNU sed you could use an address with a step, e.g.

carlo@host:/tmp -> sed '1~2s/.*/NEW TEXT &/' testfile
NEW TEXT ABCD
EFGH
NEW TEXT IJKL
MNOP
NEW TEXT PQRS
7

Thank you all for your help.

8

Yet another sed variation:

sed 's/^/extra text /;n' infile