Start with certain phrase up to certain phrase - r

Question

I have some texts and some of them actually have pre-defined templates which add no value to the analysis.
I want to use regex to systematically remove the template (which typically consist of a header text like greetings and and closing text like thank you, so that I can focus on the variable text.
Both the header and closing may have variable texts like variable location or variable staff name. So text 1 may have location equals ABC and staff name equals Sofia.
have <- "Hello, thank you for contacting our Pizza Store, <variable location>. \n\r Please find below our available menu:\nMenu 1 USD 1.99\nMenu 2 USD 3.99\n\n\n Sincerely,\nThe Awesome Pizza Team\n<variable staff name>\nDelivering Pizza 24/7"
want <- "\nMenu 1 USD 1.99\nMenu 2 USD 3.99\n"
header <- "Hello, thank you for contacting our Pizza Store, <variable location>. \n\r Please find below our available menu:"
tail <- "\n\n Sincerely,\nThe Awesome Pizza Team\n<variable staff name>\nDelivering Pizza 24/7"
Current attempt I have is as below.
# remove everything before 'menu'
gsub('(.*)menu:','', have)
# want to correct the above to
# remove everything that
# starts with "Hello, thank you for contacting" up to "Please find our available menu"
# remove everything after Sincerely, inclusive
gsub('Sincerely.*','', have)
# want to correct the above to
# remove everything that
# starts with "Sincerely,\nThe Awesome Pizza Team" up to "\nDelivering Pizza 24/7"
2nd attempt
# text
have <- "Hello, thank you for contacting our Pizza Store, <variable location>. \n\r Please find below our available menu:\nMenu 1 USD 1.99\nMenu 2 USD 3.99\n\n\n Sincerely,\nThe Awesome Pizza Team\n<variable staff name>\nDelivering Pizza 24/7"
# remove any text in between 'Hello, thank you for contacting`
# up to 'Please find below our available menu:'
# and also the anchoring texts
(want <- gsub(pattern = '(Hello, thank you for contacting).*(Please find below our available menu:)',''
, x = have))
# remove any text after `\n\n Sincerely,\nThe Awesome Pizza Team\n`, inclusive the text itself
(want <- gsub(pattern = '\n\n Sincerely,\nThe Awesome Pizza Team\n.*',''
, x = want))

Answer 1

An option might be to match all lines before Menu. Then capture all consecutive lines that start with Menu and match the rest of the lines starting at Sincerely.
In the replacement use capture group 1.
^[\s\S]*?\R((?:Menu .*\R+)*)\s*Sincerely,[\s\S]*
The pattern matches:
^Start of string
[\s\S]*?\R Match any char as least as possible followed by a newline
( Capture group 1
(?:Menu .*\R+)* Repeat matching all lines that start with Menu and match a newline
) Close group 1
\s* Match optional whitespace chars
Sincerely, Match literally
[\s\S]* Match the rest of the lines
Regex demo | R demo
Example
have <- "Hello, thank you for contacting our Pizza Store, <variable location>. \n\r Please find below our available menu:\nMenu 1 USD 1.99\nMenu 2 USD 3.99\n\n\n Sincerely,\nThe Awesome Pizza Team\n<variable staff name>\nDelivering Pizza 24/7"
trimws(gsub('^[\\s\\S]*?\\R((?:Menu .*\\R+)*)\\s*Sincerely,[\\s\\S]*','\\1', have, perl = TRUE))
Output
[1] "Menu 1 USD 1.99\nMenu 2 USD 3.99"
A bit longer an more precise pattern could be:
^(?:(?!Menu ).*(?:\R(?!Menu ).*)*\R+)?(Menu .*(?:\RMenu .*)*)\R\s*Sincerely,[\s\S]*
Regex demo | R demo