Pattern to get string between two specific words/characters using grep [duplicate]

Answer 1

Using grep -oP:

s=' from=someuser@somedomain.com, '
grep -oP '(?<=from=).*?(?=,)' <<< "$s"
someuser@somedomain.com

OR else avoid lookbehind by using \K:

grep -oP 'from=\K.*?(?=,)' <<< "$s"
someuser@somedomain.com

In case your grep doesn't support -P (PCRE) use this sed:

sed 's/.*from=\(.*\),.*/\1/' <<< "$s"
someuser@somedomain.com