Bash/sed: delete everything from text file except match(es) - regex

Question

I have a text file which I need to extract a match from in a bash script. There might be more than one match and everything else is supposed to be discarded.
Sample snippet of input.txt file content:
PART TWO OF TWO PARTS-
E RESNO 56/20 56/30 54/40 52/50 TUDEP
EAST LVLS NIL
WEST LVLS 310 320 330 340 350 360 370 380 390
EUR RTS WEST NIL
NAR NIL-
REMARKS.
1.TMI IS 142 AND OPERATORS ARE REMINDED TO INCLUDE THE
TMI NUMBER AS PART OF THE OCEANIC CLEARANCE READ BACK.
2.ADS-C AND CPDLC MANDATED OTS ARE AS FOLLOWS
TRACK A 350 360 370 380 390
TRACK B 350 360 370 380 390
I try to match for 142 from the line
1.TMI IS 142 AND OPERATORS ARE REMINDED TO INCLUDE THE
The match is always a number (one to three digits, may have leading zeroes) and always preceded by TMI IS.
My experiments so far led to nothing: I tried .*TMI IS ([0-9]+).* with the following sed command in my bash script
sed -n 's/.*TMI IS \([0-9]+\).*/\1/g' input.txt > output.txt
but only got an empty output.txt.
My script runs in GNU Bash-4.2. Where do I make my mistake? I ran out of ideas so your input is highly appreciated!
Thanks,
Chris

Answer 1

Two moments about your sed approach to make it work:
+ quantifier should be escaped in sed basic regular expressions
to print matched pattern use p subcommand:
sed -n 's/.*TMI IS \([0-9]\+\).*/\1/gp' input.txt
142
To get only the first match for your current format use:
sed -n 's/^\S\+TMI IS \([0-9]\+\).*/\1/gp' input.txt

Answer 2

With GNU grep:
$ grep -oP 'TMI IS \K([0-9]*)' input.txt
142

Answer 3

You could also do this using perl as an alternative to the above:
$ perl -nle 'print $1 if /TMI IS (\d+)/;' < input.txt
142