Shell Learning-basics (variables, inputs, outputs, arrays, environment variables)

1, #. /bin/sh Opening

2. Variables:

(1) Definition: variable name = string. Note: = no spaces around; name= "Hello World" for which a string with spaces is assigned;

(2) Citation: Use $nametest, ${name}test.

3. Wildcard characters:

(1) * symbol: Used to match the string 0 times or more occurrences; the matching. and \ symbols must be indicated. such as *test cannot match. EXtest, but to use. Ex*;*test can not match/home/test, to use/*/test.

(2). Symbol: matches only one character in the corresponding position

(3) [] symbol: matches any one of the characters in the range specified by the character group

(4). Symbol: matches any one character that is not within the bounds of the character group

4. Shell input:

Read Variable 1 variable 2

#!/bin/sh
echo "Input your name and age:"
Read Name Age
echo "Name is:" $name
echo "Age is:" $age

5. Shell output:

Echo

6. Shell array: Supports one-dimensional array, but does not qualify the size of the array.

(1) General way to take value: ${array name [subscript value]}

(2) Assignment method: array name [subscript value]= Value

(3) can be assigned a value, but also the overall assignment, but the value and value are separated by a space. Array name = (value1 value2 value3 ... ）。

eg

#!/bin/sh
Name= (I am very happy)
echo "Name[0] is:" ${name[0]}
echo "name[1] is:" ${name[1]}
echo "name[2] is:" ${name[2]}
echo "Name[3] is:" ${name[3]}

(4) You can output the value by subscript, or you can use the * and the @ symbol instead of subscript, such as ${name[*]} to take out the values of all the elements in the array.

#!/bin/sh
Name= (I am very happy)
echo "Name is" ${name[*]}
echo "Name1 is" ${name[@]}

(5) above is how to add, read, the following describes how to modify, delete.

A. Modify the re-assignment of the specified elements to an array;

B, delete need to use an external command: unset. unset name[0] To empty the element labeled 0, or you can use the unset name[@] command to cancel all elements in the array.

#!/bin/sh
Name= (I am very happy)
Name[0]=myself
Echo ${name[@]}

Unset Name[0]
Echo ${name[@]}

Unset name[@]
Echo ${name[*]}

Name[0]=hello
Name[1]=world
Echo ${name[*]}

Operation Result:

Myself am very happy
Am very happy

Hello World

6. Environment variables: There is a public space in Linux that is dedicated to storing environment variables that users can view through printenv.

(1) Basic Environment variables:

PWD, HOME, LOG NAME, SHELL, PATH

(2) Deletion of environment variables:

With the unset command, Eg:unset path is empty.

#!/bin/sh
echo "PWD:" $PWD
echo "Path:" $PATH
echo "LogName:" $LOGNAME
echo "SEHLL:" $SHELL
echo "Home:" $HOME

Operation Result:

Pwd:/home/test/shell
Path:/usr/lib64/qt-3.3/bin:/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin
Logname:root
Sehll:/bin/bash
Home:/root