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linuxmacoszshtailhead

Negative arguments to head

I was trying using head command, in macOS using zsh, code below,

a.txt:

1
2
3
4
5
6
7
8
9
10

tail -n +5 a.txt   // line 5 to line end

tail -n -5 a.txt   // last line 5 to line end

head -n +5 a.txt // line 1 to line 5

head -n -5 a.txt  // # What did this do?

The last command shows an error.

head: illegal line count -- -5

What did head -n -5 actually do?

Solution

  • Some implementations of head like GNU head support negative arguments for -n

    But that's not standard! Your case is clearly not supported.

    When supported The negative argument should remove the last 5 lines before doing the head