amosli@amosli-pc:~/learn/fd$ 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=[-]K         print the first K bytes of each file;with the leading `-', print all but the lastK bytes of each file-n, --lines=[-]K         print the first K lines instead of the first 10;with the leading `-', print all but the lastK lines of each file-q, --quiet, --silent    never print headers giving file names-v, --verbose            always print headers giving file names--help     display this help and exit--version  output version information and exitK 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.

head [OPTION]... [FILE]...

amosli@amosli-pc:~/learn/fd$ cat -n test.txt 1    a2    b3    c4    d5    e6    f7    g8    h9    i10    j11    k12    l13    m14    n

amosli@amosli-pc:~/learn/fd$ head test.txt
a
b
c
d
e
f
g
h
i
j

amosli@amosli-pc:~/learn/fd$ head -n 3 test.txt
a
b
c

  -n, --lines=[-]K         print the first K lines instead of the first 10;                   

amosli@amosli-pc:~/learn/fd$ head -n -3 test.txt
a
b
c
d
e
f
g
h
i
j
k

  -n, --lines=[-]K         print the first K lines instead of the first 10; with the leading `-', print all but the lastK lines of each file

amosli@amosli-pc:~/learn/fd$ head -c 2 test.txt
a

  -c, --bytes=[-]K         print the first K bytes of each file;

amosli@amosli-pc:~/learn/fd$ head -c -2 test.txt
a
b
c
d
e
f
g
h
i
j
k
l
m

  -c, --bytes=[-]K         print the first K bytes of each file;with the leading `-', print all but the lastK bytes of each file

amosli@amosli-pc:~/learn/fd$ head -q test.txt
a
b
c
d
e
f
g
h
i
j

  -q, --quiet, --silent    never print headers giving file names

amosli@amosli-pc:~/learn/fd$ head -v test.txt
==> test.txt <==
a
b
c
d
e
f
g
h
i
j

  -v, --verbose            always print headers giving file names

amosli@amosli-pc:~/learn/fd$ head --verbose test.txt
==> test.txt <==
a
b
c
d
e
f
g
h
i
j

amosli@amosli-pc:~/learn/fd$ head -n 3 test.txt test2.txt
==> test.txt <==
a
b
c==> test2.txt <==
c
d
e

amosli@amosli-pc:~/learn/fd$ tail --help
Usage: tail [OPTION]... [FILE]...
Print the last 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=K            output the last K bytes; alternatively, use -c +Kto output bytes starting with the Kth of each file-f, --follow[={name|descriptor}]output appended data as the file grows;-f, --follow, and --follow=descriptor areequivalent-F                       same as --follow=name --retry-n, --lines=K            output the last K lines, instead of the last 10;or use -n +K to output lines starting with the Kth--max-unchanged-stats=Nwith --follow=name, reopen a FILE which has notchanged size after N (default 5) iterationsto see if it has been unlinked or renamed(this is the usual case of rotated log files).With inotify, this option is rarely useful.--pid=PID            with -f, terminate after process ID, PID dies-q, --quiet, --silent    never output headers giving file names--retry              keep trying to open a file even when it is orbecomes inaccessible; useful when following byname, i.e., with --follow=name-s, --sleep-interval=N   with -f, sleep for approximately N seconds(default 1.0) between iterations.With inotify and --pid=P, check process P atleast once every N seconds.-v, --verbose            always output headers giving file names--help     display this help and exit--version  output version information and exitIf the first character of K (the number of bytes or lines) is a `+',
print beginning with the Kth item from the start of each file, otherwise,
print the last K items in the file.  K 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.With --follow (-f), tail defaults to following the file descriptor, which
means that even if a tail'ed file is renamed, tail will continue to track
its end.  This default behavior is not desirable when you really want to
track the actual name of the file, not the file descriptor (e.g., log
rotation).  Use --follow=name in that case.  That causes tail to track the
named file in a way that accommodates renaming, removal and creation.

tail [OPTION]... [FILE]...

amosli@amosli-pc:~/learn/fd$ cat -n test2.txt 1    c2    d3    e4    f5    g6    h7    i8    j9    k10    l11    m12    n

  -c, --bytes=K            output the last K bytes; alternatively, use -c +Kto output bytes starting with the Kth of each file

amosli@amosli-pc:~/learn/fd$ tail -c 4 test2.txt
m
n

amosli@amosli-pc:~/learn/fd$ tail -c +4 test2.txt e
f
g
h
i
j
k
l
m
n

 -n, --lines=K            output the last K lines, instead of the last 10;or use -n +K to output lines starting with the Kth--max-unchanged-stats=Nwith --follow=name, reopen a FILE which has notchanged size after N (default 5) iterationsto see if it has been unlinked or renamed(this is the usual case of rotated log files).With inotify, this option is rarely useful.--pid=PID            with -f, terminate after process ID, PID dies

amosli@amosli-pc:~/learn/fd$ tail -n 3 test2.txt
l
m
n

amosli@amosli-pc:~/learn/fd$ tail -n +3 test2.txt
e
f
g
h
i
j
k
l
m
n

 -q, --quiet, --silent    never output headers giving file names--retry              keep trying to open a file even when it is orbecomes inaccessible; useful when following byname, i.e., with --follow=name

amosli@amosli-pc:~/learn/fd$ tail -q  test2.txt
e
f
g
h
i
j
k
l
m
n

amosli@amosli-pc:~/learn/fd$ tail -v test2.txt
==> test2.txt <==
e
f
g
h
i
j
k
l
m
n

amosli@amosli-pc:~/learn/fd$ tail -f test2.txt
g
h
i
j
k
l
m
n
o
p

amosli@amosli-pc:~/learn/fd$ echo  'xyz' >> test2.txt

amosli@amosli-pc:~/learn/fd$ tail -f test2.txt
g
h
i
j
k
l
m
n
o
p
xyz

-s, --sleep-interval=N   with -f, sleep for approximately N seconds(default 1.0) between iterations.With inotify and --pid=P, check process P atleast once every N seconds.

amosli@amosli-pc:~/learn/fd$ tail -f -s 5 test2.txt
j
k
l
m
n
o
p
xyz

$PID=$(pidof Foo)
$tail -f file --pid $PID
#当进程Foo结束之后，tail也会跟着结束

amosli@amosli-pc:~/learn/fd$ PID=$(pidof gedit)
amosli@amosli-pc:~/learn/fd$ tail -f -s 2 test2.txt --pid $PID
h
i
j
k
l
m
n
o
p
xyz

[root@xiaoma /root/mcw] test!
#vim test.txt

[root@xiaoma /root/mcw] test!
#cat test.txt
1 ma
2 chang
3 wei
4 mo
5 jiang

[root@xiaoma /root/mcw] test!
#cat test.txt |head -4|tail -2 >test1.txt

[root@xiaoma /root/mcw] test!
#cat test1.txt
3 wei
4 mo