Shell中的一些常用指令整理汇总（1）
nohup 命令：不中断地运行指令
man nohup查看一下帮助文档：
NOHUP(1) User Commands NOHUP(1)
NAME
nohup - run a command immune to hangups, with output to a non-tty
SYNOPSIS
nohup COMMAND [ARG]...
nohup OPTION
DESCRIPTION
Run COMMAND, ignoring hangup signals.
--help display this help and exit
--version
output version information and exit
If standard input is a terminal, redirect it from /dev/null. If stan-
dard output is a terminal, append output to ‘nohup.out’ if possible,
‘$HOME/nohup.out’ otherwise. If standard error is a terminal, redirect
it to standard output. To save output to FILE, use ‘nohup COMMAND >
FILE’.
NOTE: your shell may have its own version of nohup, which usually
supersedes the version described here. Please refer to your shell’s
documentation for details about the options it supports.
AUTHOR
Written by Jim Meyering.
可以看出，nohup的作用是，让后面执行的cmd不受终端关闭或者账户退出的影响。如果不指定输出，那么默认会把标准输出为terminal的部分内容重定向到一个nohup.out文件，也可以用>对保存输出文件进行指定。如果时远程执行shell指令，且担心关闭xshell等终端后程序跟着自动停止的，可以实用nohup指令避免这种情况。
& 指令：后台运行程序
对于不需要交互的且时间较长的程序，可以放在后台运行，从而空出终端的交互界面。
如：
$ ls &
[1] 30048
anaconda3 anaconda-ks.cfg bash install.log install.log.syslog myinit
[1]+ Done ls --color=auto
对于ls这个指令，后台运行，给了一个pid号，然后运行结束。
head指令：查看文件前面几行
首先创建一个test.txt文件：
vim test.txt
写入如下内容：
123
124
125
通过head命令查看前面2行
head -2 test.txt
123
124
wc : 统计文档字数/行数/字节数/字符数
仍然是对test.txt，我们利用wc查看文档的字符数统计信息：
WC(1) User Commands WC(1)
NAME
wc - print newline, word, and byte counts for each file
SYNOPSIS
wc [OPTION]... [FILE]...
wc [OPTION]... --files0-from=F
DESCRIPTION
Print newline, word, and byte counts for each FILE, and a total line if more than one FILE is specified. With
no FILE, or when FILE is -, read standard input.
-c, --bytes
print the byte counts
-m, --chars
print the character counts
-l, --lines
print the newline counts
--files0-from=F
read input from the files specified by NUL-terminated names in file F; If F is - then read names from
standard input
-L, --max-line-length
print the length of the longest line
-w, --words
print the word counts
--help display this help and exit
--version
output version information and exit
实验一下：
$ wc -lmcw test.txt
3 3 12 12 test.txt
2019-08-01 10:57:20
cat 命令：连接和输入
cat可以用于将两个文件concat起来，也可以用于在键盘创建一个文件
CAT(1) User Commands CAT(1)
NAME
cat - concatenate files and print on the standard output
SYNOPSIS
cat [OPTION]... [FILE]...
DESCRIPTION
Concatenate FILE(s), or standard input, to standard output.
-A, --show-all
equivalent to -vET
-b, --number-nonblank
number nonempty output lines
-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
创建方法如下：
cat > filename.txt
然后键盘接入内容，完成后ctrl+d退出。
比如我们创建了test2.txt：
$ head test2.txt
123
124
125
126
127
133
666
-n 标记行号
-s 压缩多行空行为一行
-b 只对non-blank非空行编号
$ cat -n test2.txt
1 123
2 124
3 125
4 126
5
6
7 127
8
9 133
10 666
$ cat -b test2.txt
1 123
2 124
3 125
4 126
5 127
6 133
7 666
$ cat -s test2.txt
123
124
125
126
127
133
666
2019-08-01 11:15:26