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linux系統內置命令可以通過以下兩種方式查詢:“cat --help” 或者“man cat”。
cat命令的常用選項和官方解釋如下:
cat file_name 顯示文件全部內容
cat -b file_name 顯示文件非空行內容
cat -E file_name 在文件每行末尾顯示$,常用于管道功能
cat -n file_name 顯示內容和行號
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命令及其選項如下:
head -c10 file_name 顯示一開始的10個字節
head -c-10 file_name 顯示除末尾10個字節之外的內容
head -n10 file_name 顯示一開始的10行內容
head -n-10 file_name 顯示除末尾的10行之外的內容
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命令及其選項如下:
tail -c10 file_name 顯示末尾的10個字節
tail -c-10 file_name 顯示除開頭10個字節之外的內容
tail -n10 file_name 顯示末尾的10行內容
tail -n-10 file_name 顯示除開頭的10行之外的內容
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,這三個命令常常與管道功能搭配,用于文件內容的操作,例如:
對data.txt中的數據進行排序:cat data.txt | sort
對data.txt中的內容匹配:cat data.txt | grep 'a'
輸出data.txt中的非空行數:cat -b data.txt | wc -l
總結
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