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Comment by taeric | Hacker News Reader

Out of curiosity, I'm interested in how folks would do the "in this not that" folder query. At a gut shot, I'd assume that diff would be used. I'm about to dig through the find man page to see if it has something directly to help.

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One tool for this is the 'comm' utility: given two files containing sorted lines, it can output one or more of (1) lines only in file 1, (2) lines only in file 2, and (3) lines common to both files.

Assuming no dups in file1, this outputs lines in file1 that aren't in file2:

    sort file1 file2 file2 | uniq -u

(double file2 is not a typo :)

Or (a little faster):

  comm -23 <(sort file1) <(sort file2)

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