lowercase

To print all lines that contain only lower case characters, we used the following regular expression in grep:

egrep '^[[:lower:]]+$' <file>;
#If you do not have egrep, use
grep -e '^[[:lower:]]+$' <file>;

Breakdown of the above regular expression:

• ^ instructs the regular expression parser that the pattern should always start with the beginning of the line
• [[:lower:]] this special instruction informs us that only lower case characters can match it
• + the plus sign causes the preceding token to be matched one or more times
• $ signifies the end of the line