Grep for Keyword1Keyword2 but not Keyword1TEXTKeyword2 - Very large grep - bash

Question

I want to be able to grep for exact match results without outputting those with text in between my searched words. the middle being part of the output. For example:
egrep -i "^cat|^dog" list.txt >> startswith.txt
egrep -i "home$|house$" startswith.txt >> final.txt
I want this to return any matches for cathome, cathouse, doghome, doghouse; but not return cathasahome, catneedsahouse, etc. Take note that the files would be wayyy to big for me to go through and say ^word1word2$ in every combination.
Is there a way to do this within grep or egrep.

Answer 1

Use some grouping to specify both parts of your pattern, The anchors (^ and $) will apply to the groups.
$ cat list.txt
cathome
cathouse
catindahouse
dogindahome
doghouse
doghome
$ egrep -i "^(dog|cat)(home|house)$" list.txt
cathome
cathouse
doghouse
doghome
You could try the same thing in Perl regex mode, with non-capturing groups (since you don't care about capturing them):
$ grep -Pi "^(?:dog|cat)(?:home|house)$" list.txt
No idea if that'll make a difference either way, but doesn't hurt to try.

Answer 2

You didn't provide any sample input or expected output so this is an untested guess but this is probably what you're looking for:
awk '
BEGIN {
split("cat dog",beg)
split("home house",end)
for (i in beg)
for (j in end)
matches[beg[i] end[j]]
}
tolower($0) in matches
' file
e.g.:
$ cat file
acathome
CatHome
catinhouse
CATHOUSE
doghomes
dogHOME
dogathouse
DOGhouse
$ awk '
BEGIN {
split("cat dog",beg)
split("home house",end)
for (i in beg)
for (j in end)
matches[beg[i] end[j]]
}
tolower($0) in matches
' file
CatHome
CATHOUSE
dogHOME
DOGhouse