Little more than a week ago, I began to think about pairs of commands, foobar and unfoobar. They are like yins and yangs, they complete each other, make things come full circle, from Wikipedia:
In Chinese philosophy, the concept of yin-yang (simplified Chinese: 阴阳; traditional Chinese: 陰陽; pinyin: yīnyáng), which is often called “yin and yang”, is used to describe how opposite or contrary forces are interconnected and interdependent in the natural world; and, how they give rise to each other as they interrelate to one another.
Or you can see them as one countering another, if you are negative.
Pairs
1 cat and tac
One concatenates lines in the order of given file list, another reverses order of lines:
$ cat test.txt 123 === ABC $ tac test.txt ABC === 123
2 cat and rev
Differ than above, rev keeps the order, but reverses the order of characters in each line:
$ rev test.txt 321 === CBA
3 cat and split
One concatenates into one, another breaks into pieces:
$ split -l 1 test.txt test- $ more test-* | cat :::::::::::::: test-aa :::::::::::::: 123 :::::::::::::: test-ab :::::::::::::: === :::::::::::::: test-ac :::::::::::::: ABC
4 head and tail
One goes from beginning, another goes for the end, or toss a coin?
5 uniq -u and uniq -d/-D
One option for unique lines, another for duplicate lines:
$ cat test.txt 1 2 2 $ uniq -u test.txt 1 $ uniq -d test.txt 2 $ uniq -D test.txt 2 2
6 expand and unexpand
Tabs to spaces, spaces back to tabs, special case PEP8.
7 true and false
True yin and yang, or false?
8 Other foobars and unfoobars
Commands like compress and uncompress for compressions, encryptions, those sorts of pairs. Or variables, aliases like alias and unalias.
9 Any more?
Leave the pairs in comments below.
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