Por que o n ' t “ head -1 ” é equivalente a “ head -n -1 ” mas, em vez disso, ' é o mesmo que “ head -n 1 ”?

head -num é o mesmo que head -n num em vez de head -n -num (onde num é qualquer número)

Exemplo:

$ echo -e "a\nb\nc\nd"|head -1 a $ echo -e "a\nb\nc\nd"|head -n 1 a $ echo -e "a\nb\nc\nd"|head -n -1 a b c 

Isso head -1 não parece estar documentado em lugar nenhum.

$ head --help

Usage: head [OPTION]... [FILE]... Print the first 10 lines of each FILE to standard output. With more than one FILE, precede each with a header giving the file name. With no FILE, or when FILE is -, read standard input. Mandatory arguments to long options are mandatory for short options too. -c, --bytes=[-]NUM print the first NUM bytes of each file; with the leading "-", print all but the last NUM bytes of each file -n, --lines=[-]NUM print the first NUM lines instead of the first 10; with the leading "-", print all but the last NUM lines of each file -q, --quiet, --silent never print headers giving file names -v, --verbose always print headers giving file names -z, --zero-terminated line delimiter is NUL, not newline --help display this help and exit --version output version information and exit NUM may have a multiplier suffix: b 512, kB 1000, K 1024, MB 1000*1000, M 1024*1024, GB 1000*1000*1000, G 1024*1024*1024, and so on for T, P, E, Z, Y. GNU coreutils online help: <https://www.gnu.org/software/coreutils/> Full documentation at: <https://www.gnu.org/software/coreutils/head> or available locally via: info "(coreutils) head invocation" 

Página do manual para head (no Fedora 28):

HEAD(1) User Commands HEAD(1) NAME head - output the first part of files SYNOPSIS head [OPTION]... [FILE]... DESCRIPTION Print the first 10 lines of each FILE to standard output. With more than one FILE, precede each with a header giving the file name. With no FILE, or when FILE is -, read standard input. Mandatory arguments to long options are mandatory for short options too. -c, --bytes=[-]NUM print the first NUM bytes of each file; with the leading "-", print all but the last NUM bytes of each file -n, --lines=[-]NUM print the first NUM lines instead of the first 10; with the leading "-", print all but the last NUM lines of each file -q, --quiet, --silent never print headers giving file names -v, --verbose always print headers giving file names -z, --zero-terminated line delimiter is NUL, not newline --help display this help and exit --version output version information and exit NUM may have a multiplier suffix: b 512, kB 1000, K 1024, MB 1000*1000, M 1024*1024, GB 1000*1000*1000, G 1024*1024*1024, and so on for T, P, E, Z, Y. AUTHOR Written by David MacKenzie and Jim Meyering. REPORTING BUGS GNU coreutils online help: <https://www.gnu.org/software/coreutils/> Report head translation bugs to <https://translationproject.org/team/> COPYRIGHT Copyright © 2017 Free Software Foundation, Inc. License GPLv3+: GNU GPL version 3 or later <https://gnu.org/licenses/gpl.html>. This is free software: you are free to change and redistribute it. There is NO WARRANTY, to the extent permitted by law. SEE ALSO tail(1) Full documentation at: <https://www.gnu.org/software/coreutils/head> or available locally via: info "(coreutils) head invocation" GNU coreutils 8.29 December 2017 HEAD(1)