$ cat <<EOF > test.in
one o n e
two t w o
three t h r e e
EOF

$ perl -pe 's/(\w+)/\U$1/' < test.in > test.out

$ cat test.out
ONE o n e
TWO t w o
THREE t h r e e


##</code><code>##

$ cat <<EOF > upcase-firstword
#!/usr/bin/perl -p
s/(\w+)/\U$1/;
EOF

$ chmod +x upcase-firstword

$ upcase-firstword < test.in > test2.out

$ diff test.out test2.out