Use awk with a flag to trigger the print when necessary:

$ awk '/abc/{flag=1;next}/mno/{flag=0}flag' file
def1
ghi1
jkl1
def2
ghi2
jkl2

How does this work?

/abc/ matches lines having this text, as well as /mno/ does.
/abc/{flag=1;next} sets the flag when the text abc is found. Then, it skips the line.
/mno/{flag=0} unsets the flag when the text mno is found.
The final flag is a pattern with the default action, which is to print $0: if flag is equal 1 the line is printed.

For a more detailed description and examples, together with cases when the patterns are either shown or not, see How to select lines between two patterns?.

Ce tuto est bien fait
Mais j'ai un peu de mal avec awk : pour des tâches simple je m'en sors avec cut, et pour des tâches plus complexes je passe à un vrai langage de scripting comme python

| awk '{total = total + $1}END{print total}'

find . ! -newer /tmp/file2015 -exec ls -l --block-size=M {} \; |cut -d' ' -f5|sed 's/M//'| awk '{total = total + $1}END{print total}'

exemple de split file avec awk