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$ cat ipsum.txt | perl -ne 'print map("$_\n", m/\w+/g);' | tr A-Z a-z | sort | uniq | awk 'length($1) == 4 {print}'
Jan. 29, 2012, 10:28 p.m.
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Janos
Explanation
- The perl regex pattern
m/\w+/g will match consecutive non-word characters, resulting in a list of all the words in the source string
map("$_\n", @list) transforms a list, appending a new-line at the end of each elementtr A-Z a-z transforms uppercase letters to lowercase- In awk,
length($1) == 4 {print} means: for lines matching the filter condition "length of the first column is 4", execute the block of code, in this case simply print
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