mjhjmtu

So what I would need is for grep to match only the text in between (and including) my match pattern.

So something like this (don't mind the text, it's just some garble :D):

asdgfasd gasd gdas g This will be this one day ksjadnbalsdkbgas asd gasdg 
asdgasdgasdg dasg dasg dasg This will be this next day adf gdsf gdsf sdfh dsfhdfsh
asdf asdf asd fesf dsfasd f This will won' not this day asdgadsgaseg as dvf as d vfa se v asd
dasfasdfdas fase fasdfasefase fasdf This not what shoes day asdjbna;sdgbva;sdkbcvd;lasb ;lkbasi hasdli glais g

So what I want is something like this:
cat theabovetext|grep -E "^This * day$"
To output this:

This will be this one day
This will be this next day
This will won' not this day
This not what shoes day

So basically I want to ONLY get the text in between This and Day (including This and day) regardless of how many characters there are in between, and regardless of how many characters there are before This and after Day.
Also this needs to work even if the input is all on a single line, so this:

asdgfasd gasd gdas g This will be this one day ksjadnbalsdkbgas asd gasdg asdgasdgasdg dasg dasg dasg This will be this next day adf gdsf gdsf sdfh dsfhdfsh asdf asdf asd fesf dsfasd f This will won' not this day asdgadsgaseg as dvf as d vfa se v asd dasfasdfdas fase fasdfasefase fasdf This not what shoes day asdjbna;sdgbva;sdkbcvd;lasb ;lkbasi hasdli glais g

Has to output this:

This will be this one day This will be this next day This will won' not this day This not what shoes day

N.B. the output here is still on a single line.

If you want lines to be processed separately (your first example) but for multiple matches per line to be output on a single line (as in your second example), then I don't think that's possible with grep alone.

However using the same This.*?day non-greedy match in perl itself you can do

$ perl -lne 'print join " ", /This.*?day/g' theabovetext1
This will be this one day
This will be this next day
This will won' not this day
This not what shoes day

while for the single-line input

$ perl -lne 'print join " ", /This.*?day/g' theabovetext2
This will be this one day This will be this next day This will won' not this day This not what shoes day

With GNU grep you could do the following:

grep -o 'This.*day' theabovetext

(note that you don't need cat since grep knows how to read files)

The -o flag says to show only the parts of the line that match the pattern.

I suspect other versions of grep support this flag as well, but it's not in POSIX, so it's not portable necessarily.

Eric Renouf's response does most of the work. And steeldriver's comment cuts out the extra text within a given line by making it non-greedy.

So it seems like: grep -oP 'This.*?day' theabovetext does everything you want except the output is on multiple lines.

To put the output on one line you could do grep -oP 'This.*?day' theabovetext | tr 'n' ' '. This addition simply replaces newline breaks with spaces*

*This will replace all output newlines with spaces. So if your initial input is line separated, these newline breaks will be lost.