linux系統(tǒng)內(nèi)置命令可以通過(guò)以下兩種方式查詢：“cat --help” 或者“man cat”。
cat命令的常用選項(xiàng)和官方解釋如下：
cat file_name 顯示文件全部?jī)?nèi)容
cat -b file_name 顯示文件非空行內(nèi)容
cat -E file_name 在文件每行末尾顯示$，常用于管道功能
cat -n file_name 顯示內(nèi)容和行號(hào)
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命令及其選項(xiàng)如下：
head -c10 file_name 顯示一開(kāi)始的10個(gè)字節(jié)
head -c-10 file_name 顯示除末尾10個(gè)字節(jié)之外的內(nèi)容
head -n10 file_name 顯示一開(kāi)始的10行內(nèi)容
head -n-10 file_name 顯示除末尾的10行之外的內(nèi)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命令及其選項(xiàng)如下：
tail -c10 file_name 顯示末尾的10個(gè)字節(jié)
tail -c-10 file_name 顯示除開(kāi)頭10個(gè)字節(jié)之外的內(nèi)容
tail -n10 file_name 顯示末尾的10行內(nèi)容
tail -n-10 file_name 顯示除開(kāi)頭的10行之外的內(nèi)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，這三個(gè)命令常常與管道功能搭配，用于文件內(nèi)容的操作，例如：
對(duì)data.txt中的數(shù)據(jù)進(jìn)行排序：cat data.txt | sort
對(duì)data.txt中的內(nèi)容匹配：cat data.txt | grep 'a'
輸出data.txt中的非空行數(shù)：cat -b data.txt | wc -l
總結(jié)
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