How to use comments in the shell
1. Single line comment
Single-line comments are the most common, and they are implemented through a '#'. Note that the # sign at the beginning of the shell script "#! / Bin / bash" is not for comments.
2. Multi-line comments
There is also a multi-line comment method in the shell script, which we call the "HERE DOCUMENT" feature. The format is as follows:
<<xxxx
comment 1
comment 2
啊啊啊啊
xxxx
Where xxxx can be any string. The middle part is a note. This method is often used to indicate the usage of the function, as shown in the following figure:
#########################################################################
# File Name: hereDocument.sh
# Author: sun
# mail: [email protected]
# Created Time: 2020年03月01日 星期日 11时00分27秒
#########################################################################
#!/bin/bash
<<comment
1. 可以用来多行注释
2. 常用来描述一个函数的用法说明
3. 使用任意个字符串括起来就行，不一定是comment
comment
usage(){
#如果添加一个'-'，则用来说明忽略行首的制表符
cat <<EOF
usage:commond [-x] [-v] [-z] [file ...]
a short explation of the opteration goes here;
It might be a few lines long, but shouldn't be excessive.
EOF
}
if [ $# -ne 1 ];
then
usage
exit 0
fi
length=$1
#生成随机密码
tr -dc A-Za-z0-9_ < /dev/urandom | head -c${length} | xargs
exit
