linux系统内置命令可以通过以下两种方式查询：“cat --help” 或者“man cat”。
cat命令的常用选项和官方解释如下：
cat file_name 显示文件全部内容
cat -b file_name 显示文件非空行内容
cat -E file_name 在文件每行末尾显示$，常用于管道功能
cat -n file_name 显示内容和行号
Usage: cat [OPTION]... [FILE]... Concatenate FILE(s) to standard output. With no FILE, or when FILE is -, read standard input. -A, --show-all equivalent to -vET -b, --number-nonblank number nonempty output lines, overrides -n -e equivalent to -vE -E, --show-ends display $ at end of each line -n, --number number all output lines -s, --squeeze-blank suppress repeated empty output lines -t equivalent to -vT -T, --show-tabs display TAB characters as ^I -u (ignored) -v, --show-nonprinting use ^ and M- notation, except for LFD and TAB --help display this help and exit --version output version information and exit Examples: cat f - g Output f's contents, then standard input, then g's contents. cat Copy standard input to standard output. GNU coreutils online help: <http://www.gnu.org/software/coreutils/> Full documentation at: http://www.gnu.org/software/coreutils/cat
head命令及其选项如下：
head -c10 file_name 显示一开始的10个字节
head -c-10 file_name 显示除末尾10个字节之外的内容
head -n10 file_name 显示一开始的10行内容
head -n-10 file_name 显示除末尾的10行之外的内容
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: <http://www.gnu.org/software/coreutils/>
Full documentation at: http://www.gnu.org/software/coreutils/head
tail命令及其选项如下：
tail -c10 file_name 显示末尾的10个字节
tail -c-10 file_name 显示除开头10个字节之外的内容
tail -n10 file_name 显示末尾的10行内容
tail -n-10 file_name 显示除开头的10行之外的内容
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=[+]NUM output the last NUM bytes; or use -c +NUM to
output starting with byte NUM of each file
-f, --follow[={name|descriptor}]
output appended data as the file grows;
an absent option argument means 'descriptor'
-F same as --follow=name --retry
-n, --lines=[+]NUM output the last NUM lines, instead of the last 10;
or use -n +NUM to output starting with line NUM
--max-unchanged-stats=N
with --follow=name, reopen a FILE which has not
changed size after N (default 5) iterations
to 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 if it is inaccessible
-s, --sleep-interval=N with -f, sleep for approximately N seconds
(default 1.0) between iterations;
with inotify and --pid=P, check process P at
least once every N seconds
-v, --verbose always output 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.
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.
GNU coreutils online help: <http://www.gnu.org/software/coreutils/>
Full documentation at: http://www.gnu.org/software/coreutils/tail
搭配管道使用更佳
此外，这三个命令常常与管道功能搭配，用于文件内容的操作，例如：
对data.txt中的数据进行排序：cat data.txt | sort
对data.txt中的内容匹配：cat data.txt | grep 'a'
输出data.txt中的非空行数：cat -b data.txt | wc -l
总结
