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From my earlier comment to the question itself:

egrep '^(pro|con).* /usr/share/dict/words | sed -nr 's/^(pro|con)(.*)/\2/p' | sort | uniq -d 

will give you a list of all the word-bases that have both a pro and con prefix:

The initial egrep grabs all the words with pro and con prefixes. We then use sed to strip off pro and con from the beginning of each word, sort the list, and then use uniq -d to show ony entries on the list that have duplicates.

From my earlier comment to the question itself:

egrep '^(pro|con).* /usr/share/dict/words | sed -nE 's/^(pro|con)(.*)/\2/p' | sort | uniq -d 

will give you a list of all the word-bases that have both a pro and con prefix:

The initial egrep grabs all the words with pro and con prefixes. We then use sed to strip off pro and con from the beginning of each word, sort the list, and then use uniq -d to show ony entries on the list that have duplicates.

From my earlier comment to the question itself:

egrep '^(pro|con).* /usr/share/dict/words | sed 's/^pro//;s/^con//' | sort | uniq -d 

will give you a list of all the word-bases that have both a pro and con prefix:

The initial egrep grabs all the words with pro and con prefixes. We then use sed to strip off pro and con from the beginning of each word, sort the list, and then use uniq -d to show ony entries on the list that have duplicates.

From my earlier comment to the question itself:

egrep '^(pro|con).* /usr/share/dict/words | sed -nr 's/^(pro|con)(.*)/\2/p' | sort | uniq -d 

will give you a list of all the word-bases that have both a pro and con prefix:

The initial egrep grabs all the words with pro and con prefixes. We then use sed to strip off pro and con from the beginning of each word, sort the list, and then use uniq -d to show ony entries on the list that have duplicates.

From my earlier comment to the question itself:

egrep '^(pro|con).* /usr/share/dict/words | sed 's/^...//' | sort | uniq -d 

will give you a list of all the word-bases that have both a pro and con prefix:

The initial egrep grabs all the words with pro and con prefixes. We then use sed to strip off the first three characters of each word, sort the list, and then use uniq -d to show ony entries on the list that have duplicates.

From my earlier comment to the question itself:

egrep '^(pro|con).* /usr/share/dict/words | sed 's/^pro//;s/^con//' | sort | uniq -d 

will give you a list of all the word-bases that have both a pro and con prefix:

The initial egrep grabs all the words with pro and con prefixes. We then use sed to strip off pro and con from the beginning of each word, sort the list, and then use uniq -d to show ony entries on the list that have duplicates.