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
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