In comp.lang.awk, Ed Morton offers advise on how to print ranges of Awk records.
Problem
Suppose you are looking to extract a section of code from a text file based on
two regular expressions.
Say the file looks like this:
newspaper
magazing
hiking
hiking trails in the city
muir hike
black mountain hike
summer meados hike
end hiking
phone
cell
skype
and you want to
extract
hiking trails in the city
muir hike
black mountain hike
summer meados hike
The following regular expression won't work right:
awk '/hiking/,/end hiking/{print}' myfile
since that returns some spurious information.
What do do?
Solution
Personally, I rarely if ever use
/start/,/end/
as I'm never immediately sure what it'd output for input such as:
start
a
start
b
end
c
end
and whenever you want to do something just slightly different with the
selection you need to change the script a lot.
Not being sure of the semantics is probably a catch 22 since I rarely
use it but the benefit of using that syntax vs spelling it out:
/start/{f=1} f; /end/{f=0}
just doesn't really seem worthwhile, and then if you want to do
something extra like test for some other condition over the block
this:
/start/{f=1} f&&cond; /end/{f=0}
is about as brief as:
/start/,/end/{if (cond) print}
and if you want to exclude the start (or end) of the block you're
printing then you just move the "f" test to the obvious place and you
don't need to duplicate the condition:
f; /start/{f=1} /end/{f=0}
vs
/start/,/end/{if (!/start/) print}
and note the different semantics now. This:
f; /start/{f=1} /end/{f=0}
will exclude the line at the start of the block you're printing,
whereas this:
/start/,/end/{if (!/start/) print}
will exclude that line plus every other occurrence of "start" within
the block which is probably not what you'd want. To simply exclude
only the first line of the block but stay with the /start/,/end/
approach you'd need to do something like:
