Have you ever wondered what files are in one folder and not in
another? Or wondered what numbers are common to two sets of
numbers? Or wanted to know what words are missing from a set?
Here's a quick-and-dirty way to query two sets in bash. Using
filenames as an example:
mkdir a b
touch a/{a,b,c,d}
touch b/{a,c,e,f}
find a b
{ ls a ; ls b ; ls b ; } | sort | uniq -c | sort -n
Now you can use grep to do simple set operations and remove the
leading numbers with "cut -c 9-".
It's not computationally efficient, but is easier to remember than
the "join" command, especially for questions like, "what's in 'a' but
not in 'b'?" Answer:
{ ls a ; ls b ; ls b ; } | sort | uniq -c | sort -n | grep '^ *1' |
cut -c 9-
Regards,
- Robert
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