egrep -wi 'am|is|are' daphne.txt
or
egrep -i ' (am|is|are) ' daphne.txt
In this case, | is the `or' operator for egrep, not the pipe. The single quotes protect it from being interpreted as the pipe by the unix shell.
(daphne.txt is in /home/corpora/english/gutenberg/etexts00.)