Unix print pattern between the Strings - unix

Question

I have a file which has got content like below. START and STOP stand for a block.
START
X | 123
Y | abc
Z | +=-
STOP
START
X | 456
Z | +%$
STOP
START
X | 789
Y | ghi
Z | !##
STOP
I would like to get the values of X and Y printed in the format below for each block:
123 ~~ abc
456 ~~
789 ~~ ghi
If it is single occurrence of START/STOP, sed -n '/START/,/STOP/p' would have helped. Since this is repetitive, I need your help.

Answer 1

Based on my own solution to How to select lines between two marker patterns which may occur multiple times with awk/sed:
awk -v OFS=" ~~ " '
/START/{flag=1;next}
/STOP/{flag=0; print first, second; first=second=""}
flag && $1=="X" {first=$3}
flag && $1=="Y" {second=$3}' file
Test
$ awk -v OFS=" ~~ " '/START/{flag=1;next}/STOP/{flag=0; print first, second; first=second=""} flag && $1=="X" {first=$3} flag && $1=="Y" {second=$3}' a
123 ~~ abc
456 ~~
789 ~~ ghi

Answer 2

Sed is always the wrong choice for any problem that involves processing multiple lines. All of sed's arcane constructs for doing so became obsolete in the mid-1970s when awk was invented.
Whenever you have name-value pairs in your input I find it useful to create an array that maps each name to it's value and then access the array by the names. In this case, using GNU awk for multi-char RS and delete array:
$ cat tst.awk
BEGIN {
RS = "\nSTOP\n"
OFS=" ~~ "
}
{
delete n2v
for (i=2;i<=NF;i+=3) {
n2v[$i] = $(i+2)
}
print n2v["X"], n2v["Y"]
}
$ gawk -f tst.awk file
123 ~~ abc
456 ~~
789 ~~ ghi

Answer 3

Because I like brain teasers (not because this sort of thing is practical to do in sed), a possible sed solution is
sed -n '/START/,/STOP/ { //!H; // { g; /^$/! { s/.*\nX | \([^\n]*\).*/\1 ~~/; ta; s/.*/~~/; :a G; s/\n.*Y | \([^\n]*\).*/ \1/; s/\n.*//; p; s/.*//; h } } }'
This works as follows:
/START/,/STOP/ { # between two start and stop lines
//! H # assemble the lines in the hold buffer
# note that // repeats the previously
# matched pattern, so // matches the
# start and end lines, //! all others.
// { # At the end
g # That is: When it is one of the
/^$/! { # boundary lines and the hold buffer
# is not empty
s/.*\nX | \([^\n]*\).*/\1 ~~/ # isolate the X value, append ~~
ta # if there is no X value, just use ~~
s/.*/~~/
:a
G # append the hold buffer to that
s/\n.*Y | \([^\n]*\).*/ \1/ # and isolate the Y value so that
# the pattern space contains X ~~ Y
s/\n.*// # Cutting off everything after a newline
# is important if there is no Y value
# and the previous substitution did
# nothing
p # print the result
s/.*// # and make sure the hold buffer is
h # empty for the next block.
}
}
}