Shell Learning (i)

One, free of dense interaction

--stdin

1. Reading strings from standard input

such as: passwd--stdin heruguo246

[Email protected] mnt]# passwd--stdin heruiguo246
Changing password for user heruiguo246.
123456 ---Input modified heruiguo246 user password is 123456
Passwd:all authentication tokens updated successfully.

2, can be from the keyboard, can also be given from another command

such as: Echo 1234567 |passwd--stdin herugiu246

[Email protected] mnt]# echo 1234567 | passwd--stdin heruiguo246
Changing password for user heruiguo246.
Passwd:all authentication tokens updated successfully.

This time there is no manual password entered, complete script implementation.

Second, ignore irrelevant output

Black hole Equipment/dev/null

A one-way file that can only be written and unreadable, and the data stored in it will be lost.

Usage: executable statement &>/dev/null

echo 1234567|passwd--stdin heruiguo246 &>/dev/null

[Email protected] mnt]# echo 1234567|passwd--stdin heruiguo246 &>/dev/null
[Email protected] mnt]#

Note that there are no spaces between:& and > and > and/dev/null, or error

Third, record error message

Usage: Executable statement 2>/path/log file name

such as: sh/mnt/adduser.sh 2>/mnt/adderror.log

Iv. Logical Segmentation

1, | | The logical relationship is "or", and any command that executes succeeds is expected, and the subsequent command executes only if the preceding command fails.

such as: ID Test | | Useradd test-Indicates that a user is created when the test user does not exist.

V. The difference between double and single quotation marks

Double quotes:

(1) in double quotes, you can use the $ extension to represent variables, such as:

[Email protected] mnt]# a=5
[[email protected] mnt]# echo "Your value is: $a"
Your value is: 5

(2) When a special character appears, you can use \ to indicate escape, \ t for tab, \ n for line break, such as:

[Email protected] mnt]# a= "a\tb\tc\td\ne\tf\tg\th"
[Email protected] mnt]#
[[email protected] mnt]# ECHO-E $a-e parameter means parsing special escape characters
A B c D
E F g H

(3) When the variable value does not include spaces, tabs, double quotes are usually omitted, such as:

[Email protected] mnt]# a=centos6.5
[Email protected] mnt]# b= $a server
-bash:server:command not found
[Email protected] mnt]# b= "$a server"
[Email protected] mnt]# echo $b
centos6.5 Server

Single quotes:

(1) All strings are treated as characters themselves (no special) such as:

[Email protected] mnt]# A=centos
[Email protected] mnt]# echo ' $a '
$a
[Email protected] mnt]#

(2) do not allow \ Escape

Vi. usage of the read fetch value

Basic format

Read variable name

READ-P "hint Information" variable name

[[email protected] mnt]# Read name
123
[Email protected] mnt]# echo $name
123
[Email protected] mnt]#
[[email protected] mnt]# read-p "Please enter your username:" Name
Please enter user name: Xiaoming
[Email protected] mnt]# echo $name
Xiaoming

Silent Value plus-S does not appear on the screen when you enter a password

[Email protected] mnt]# read-s-P "Please enter your password:" passwd
Please enter your password:
[Email protected] mnt]# echo $passwd
123456

Shell Learning (i)