grep – show lines until certain pattern

You can use sed for that:

sed -n '/if/,/endif/p' myfile

• -n don't print anything until we ask for it
• /if/ find the first line with this
• , keep going until...
• /endif/ this is the last line we want
• p print the matched lines

Traditional grep is line-oriented. To do multiline matches, you either need to fool it into slurping the whole file by telling it that your input is null terminated e.g.

grep -zPo '(?s)\nif.*\nendif' file

or use a more flexible tool such as pcregrep

pcregrep -M '(?s)\nif.*?\nendif' file

or perl itself

perl -00 -ne 'print if m/^if.*?endif/s' file

Alternatively, for matching structured input in a grep-like way, there's sgrep

sgrep '"if" .. ("endif") containing "SOME CODE"' file

A solution awk could look like: awk '/if/,/endif/' file

Of course, it is similar to the solution with sed.