人需要活得真实，放下面具，活出真实的自己。
SHELL=[ 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 ]
progress:[############## ] 70%
Ax Shell Substitution | 转义
| Sr.No. | Escape & Description |
|---|---|
| 1 | *\\* backslash |反斜杠 |
| 2 | **\a **alert (BEL) | 警告 |
| 3 | \b backspace | 空格 |
| 4 | \c suppress trailing newline | 不换行 |
| 5 | \f form feed | 换页 |
| 6 | **\n **new line | 新的一行 |
| 7 | **\r **carriage return | 回车 |
| 8 | \t horizontal tab | 制表位 |
| 9 | \v vertical tab | 垂直位 |
使用-E禁用反斜杠转义，使用-n禁用新行插入。
Command Substitution
转义为命令
`command`
例
#!/bin/sh
DATE=`date`
echo "Date is $DATE"
USERS=`who | wc -l`
echo "Logged in user are $USERS"
UP=`date ; uptime`
echo "Uptime is $UP"
执行脚本 −
Date is Thu Jul 2 03:59:57 MST 2009
Logged in user are 1
Uptime is Thu Jul 2 03:59:57 MST 2009
03:59:57 up 20 days, 14:03, 1 user, load avg: 0.13, 0.07, 0.15
Variable Substitution
| Sr.No. | Form | Description |
|---|---|---|
| 1 | ${var} | 替换var的值 |
| 2 | ${var:-word} | var未设置或为空，word将替换为var，var值不改变 |
| 3 | ${var:=word} | 如果var为空或未设置，var设置为word的值。 |
| 4 | ${var:?message} | 如果var为空或未设置，message将打印到标准错误。 这将检查变量是否设置正确。 |
| 5 | ${var:+word} | 如果设置了var，则word将替换为var。var的值不会改变。 |
例
#!/bin/sh
echo ${var:-"Variable is not set"}
echo "1 - Value of var is ${var}"
echo ${var:="Variable is not set"}
echo "2 - Value of var is ${var}"
unset var
echo ${var:+"This is default value"}
echo "3 - Value of var is $var"
var="Prefix"
echo ${var:+"This is default value"}
echo "4 - Value of var is $var"
echo ${var:?"Print this message"}
echo "5 - Value of var is ${var}"
执行脚本 −
Variable is not set
1 - Value of var is
Variable is not set
2 - Value of var is Variable is not set
3 - Value of var is
This is default value
4 - Value of var is Prefix
Prefix
5 - Value of var is Prefix
