[ILUG] [TOTD] set operations on the command line

[Pádraig Brady]

Following on from my previous mail
about finding cruft on a debian system with:
(cat /var/lib/dpkg/info*.list ; find / -type f ) | LANG=C sort | uniq -u

I find set operations like that quite common on the command line:

For unsorted files:

LANG=C sort file1 file2 | uniq              #Union
LANG=C sort file1 file2 | uniq -d           #Intersection
LANG=C sort file1 file1 file2 | uniq -u     #Difference
LANG=C sort file1 file2 | uniq -u           #Symmetric Difference

For sorted files:

LANG=C comm file1 file2 | sed 's/^\t*//'    #Union
LANG=C comm -12 file1 file2                 #Intersection
LANG=C comm -13 file1 file2                 #Difference
LANG=C comm -3 file1 file2 | sed 's/^\t*//' #Symmetric Difference

Note the LANG=C for speed as we're not interested
in the actual order of the items.

Pádraig.