Shell Basic Learning

From Shell13 asked

-E: Activate the conversion of the backslash control character (refer to the following table)

-e: Turn off anti-skew control character conversion (preset)

-N: Cancel line end of line symbol (with the \c character under the-e option)

To cancel a variable, you can use the unset command in bash to handle it:
Code: unset A
For EP:A=BCD

Echo $a

Unset $a

Variable set mode str not set STR has been set whether it is not an empty string
VAR=${STR=EXPR} str=expr Str invariant
var=expr var= $str

VAR=${STR:=EXPR} Whether or not Str has a definition, it will be redefined to assign a value

$# 是传给脚本的参数个数

$0是脚本本身的名字

$1 是传递给该shell脚本的第一个参数 $2 是传递给该shell脚本的第二个参数 [email protected] 是传给脚本的所有参数的列表 $* 是以一个单字符串显示所有向脚本传递的参数，与位置变量不同，参数可超过9个 $$ 是脚本运行的当前进程ID号 $? 是显示最后命令的退出状态，0表示没有错误，其他表示有错误

In the last two echo commands, you will find that the argument part is displayed in your fluorescence screen, and the line break
There is no difference between the "-n" option.
Obviously, the second echo is canceled by the line break, and the next shell prompt is connected to the
The results of the same line ... ^_^
In fact, Echo, in addition to the-N options, has the following common choices:
7-E: Activate the inverse of the control character conversion (refer to the following table)-e: Close the inverse of the control character conversion (this is the case)-N: Cancel line end of the line symbol (with the-e option under the \c character consent)
The following table lists the anti-skew control characters supported by the echo command:

\a:alert/bell (from the system speaker)

\b:backspace, that is, to the left to remove keys

\c: Cancel line end of line break

\e:escape, jump Keys

\f:formfeed, page character

\n:newline, replacing line characters

\r:return, back to the car keys

\t:tab, table-hopping keys

\v:vertical TAB, Vertical table-hopping keys

\N:ASCII Eight Import code (16-bit X first)

\ \: The backslash itself (tabular information from O ' Reilly publishing house learning the Bash Shell, 2nd Ed.)

Shell Basic Learning