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Select only those lines containing matches that form whole words. The test is that the matching substring must
either be at the beginning of the line, or preceded by a non-word constituent character. Similarly, it must be
either at the end of the line or followed by a non-word constituent character. Word-constituent characters are
letters, digits, and the underscore.
grep's regex also supports four special zero-width patterns: "\<","\>","\b", and "\B".
The first three match the zero-width transition between a word and a non-word character. The arrows only match in one direction (i.e. [nonword]\<[word], and [word]\>[nonword]), while "\b" matches both. They can also match at the beginning or ending of the string, like "^" and "$".
"\B" is the opposite of "\b", and only matches the transition between two characters of the same type, that is two word characters together or two non-word characters together. I only mention it for completeness, as it isn't useful here.
Finally, remember that a "word" character is a-z, A-Z, 0-9, and _ (underscore). This cannot be changed, so things can get trickier if you have to redefine what a word is.