Parsing list in bash - bash

Question

I have a text file which looks like this:
...
unique_trigger = item1
item2
item3
...
itemN
unique_end_trigger
...
Is there a quick (maybe on-liner if possible) bash script I could use to parse the file and pipe item1 item2 item3... into another command? The number of items is not determined. I looked at other bash scripts to read variables out of a file but they either source it, parse each item manually (predetermined list length) or assign a environment variable to each item based on its name (which is not my case). I am looking for something like this:
parse_command file.txt | other_command

Answer 1

perl:
perl -0777 -pE 's/.*unique_trigger\s*=\s*(.*)unique_end_trigger.*/$1/s; s/^\s+//gm' file.txt
item1
item2
item3
...
itemN

Answer 2

One-liner
cat file.txt | tr -s "[:space:]" " " | \
sed -En "s/(.*)(unique_trigger = )(.*)(unique_end_trigger)/\3/p" | \
other_command

Answer 3

awk '/unique_end_trigger/&&--f||f||/unique_trigger/&&f++ {printf $1 " "}' <(sed 's/unique_trigger =/ & \n /' input_file)
item1 item2 item3 ... itemN

Answer 4

Not quite a one-liner, but it should do the trick as long as your triggers don't contain spaces.
flag=0
while read tr eq it ; do
if [ "$tr" = "unique_trigger" ] ; then
echo "$it"
flag=1
elif [ $flag = 1 ] ; then
if [ "$tr" = "unique_end_trigger" ] ; then
flag=0
else
echo "$tr"
fi
fi
done

Answer 5

Two solutions, using the same concept. When the start trigger is found, add the item (3rd item in the line) to a string. Until the end trigger is found, the item is the only work in the line, so add it to the string. Output the string at the end.
Bash parsing
#!/bin/bash
file="file.txt"
start_trigger="unique_trigger"
end_trigger="unique_end_trigger"
items=''
between_trigger="no"
while IFS= read -r line; do
#echo "-----$line-----"
# Start trigger lines
if [[ "$line" =~ "$start_trigger =" ]]
then
items="$items $(echo "$line" | awk '{print $3}')"
between_trigger="yes"
continue
fi
# End trigger lines
if [[ "$line" =~ "$end_trigger" ]]
then
between_trigger="no"
continue
fi
# Lines between start and end trigger
if [[ "$between_trigger" == "yes" ]]
then
items="$items $line"
continue
fi
done < "$file"
echo ">>$items<<"
Using it: script.bash | xargs echo
Replace echo by any command.
Awk version
BEGIN {
output = ""
between = "no"
}
/unique_end_trigger/ {
between = "no";
}
/.*/ {
if (between == "yes") output = output " " $1
}
/unique_trigger/ {
between = "yes";
output = output " " $3;
}
END { print output }
Using it: awk -f script.awk file.txt | xargs echo
Replace echo with whatever command you want.