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Shell Learning Notes (2)

Last Update:2018-03-15 Source: Internet

Author: User

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I. Standard input commands read and Practice 1, read basic usage

[root@master4 day3]# vim read.sh

read -p "pls input two number:" var1 var2
echo "the nums you input is: $var1 $var2"

2. Small Script Example

[root@master4 day3]# vim read.sh

read -p "pls input two number:" var1 var2
echo "the nums you input is: $var1 $var2"

3. Set timeout period

[root@master4 day3]# vim read.sh

read -t 5 -p "pls input two number:" var1 var2
echo "the nums you input is: $var1 $var2"

[root@master4 day3]# sh read.sh 
pls input two number:the nums you input is:

4, Echo-n cooperation

[[email protected] day3]# vim echo.shecho -n "please input a num:" read numberecho $number[[email protected] day3]# sh echo.sh please input a num:4545

5, subtraction, read mode


[root@master4 day3]# vim read01.sh

#!/bin/bash
read -p "input input tow num caculate:" num1 num2
echo "$num1-$num2 = $(( $num1 - $num2))"
echo "$num1+$num2 = $(( $num1 + $num2))"
echo "$num1*$num2 = $(( $num1 * $num2))"
echo "$num1/$num2 = $(( $num1 / $num2))"
echo "$num1**$num2 = $(( $num1 ** $num2))"
echo "$num1%$num2 = $(( $num1 % $num2))"

input input tow num caculate:5 2
5-2 = 3
5+2 = 7
5*2 = 10
5/2 = 2
5**2 = 25
5%2 = 1
[root@master4 day3]#

6, conditional judgment, can only pass two parameters

#!/bin/bash
if [ $# -ne 2 ];then
    echo "USAGE:$0 NUM1 NUM2"
    exit 1
fi
#read -p "input input tow num caculate:" num1 num2
num1=$1
num2=$2
echo "$num1-$num2 = $(( $num1 - $num2))"
echo "$num1+$num2 = $(( $num1 + $num2))"
echo "$num1*$num2 = $(( $num1 * $num2))"
echo "$num1/$num2 = $(( $num1 / $num2))"
echo "$num1**$num2 = $(( $num1 ** $num2))"
echo "$num1%$num2 = $(( $num1 % $num2))"

Ii. condition Test 1, Syntax format

1.1 format 1 test< test expression >


Determine if the file exists:
[root@master4 day3]# test -f file && echo true || echo false
False
[root@master4 day3]#

[root@master4 day3]# touch file
[root@master4 day3]# test -f file && echo true || echo false
True

Does not exist, so no error:
[root@master4 day3]# rm -rf file
[root@master4 day3]# test -f file && cat file
[root@master4 day3]#
The file exists:
[root@master4 day3]# echo 1 > file
[root@master4 day3]# test -f file && cat file
1
[root@master4 day3]#

1.2 Test! (non) Usage


[root@master4 day3]# rm -rf file 
[root@master4 day3]# test ! -f file && cat file
cat: file: No such file or directory
[root@master4 day3]# 

[root@master4 day3]# echo 1 > file
[root@master4 day3]# test ! -f file && cat file
[root@master4 day3]#

1.3 View Test Help

[root@master4 day3]# help test

2, Format 2 [< test expression >]

2.1 Simple example


[root@master4 day3]# rm -rf file 
[root@master4 day3]# [ -f file ] && echo 1 || echo 0
0
[root@master4 day3]# 

存在：
[root@master4 day3]# touch file
[root@master4 day3]# [ -f file ] && echo 1 || echo 0
1
[root@master4 day3]# 

非：
[root@master4 day3]# [ ! -f file ]&&echo 1 ||echo 0
0
[root@master4 day3]#

3. Format 3:[[< test expression >]


[root@master4 day3]# [[ ! -f file ]]&&echo 1 ||echo 0
0
[root@master4 day3]#

4. &&


[root@master4 day3]# [[ -f file && -d folder ]] && echo 1 || echo 0
0
[root@master4 day3]# mkdir folder
[root@master4 day3]# [[ -f file && -d folder ]] && echo 1 || echo 0
1
[root@master4 day3]#

Format 2 error:
[root@master4 day3]# [ -f file && -d folder ] && echo 1 || echo 0
-bash: [: missing `] ‘
0
[root@master4 day3]#
Need to use this:

[root@master4 day3]# [ -f file -a -d folder ] && echo 1 || echo 0
1
[root@master4 day3]#

or
[root@master4 day3]# [ -f file ] && [ -d folder ] && echo 1 || echo 0
1
[root@master4 day3]#

3. File test operator

3.1 memory method

4, String test operators 4.1

5, two yuan comparison

5.1 two yuan comparison of special conditions example

5.2 Two-dollar string comparison

6, the logical operator 6.1 example three, example 1, the condition Test 1 is true, 0 means false

Condition and if statement comparison
[root@master4 day3]# [ -f "$file1" ] && echo 1 || echo 0
0
[root@master4 day3]# if [ -f "$file1" ];then echo 1;else echo 0;fi
0

If [ -f "$file1" ]; then
     Echo 1
Else
     Echo 0
Fi

prompt:
1. The functions of the above two statements are equivalent.
2, the variable $file added double quotes, this is a good habit of programming, can prevent many unexpected errors.

2. Document Test Example

[root@master4 day3]# file1=/etc/services
[root@master4 day3]# file2=/etc/rc.local

True if it exists and is a file
[root@master4 day3]# [ -f "$file1" ] && echo 1 || echo 0
1

True if it exists and is a directory
[root@master4 day3]# [ -d "$file1" ] && echo 1 || echo 0
0

True if the file exists and is not empty
[root@master4 day3]# [ -s "$file1" ] && echo 1 || echo 0
1

True if it exists
[root@master4 day3]# [ -e "$file1" ] && echo 1 || echo 0
1

If you remove the quotes, the test is normal:
[root@master4 day3]# [ -f $file1 ] && echo 1 || echo 0
1
[root@master4 day3]# [ -f $file2 ] && echo 1 || echo 0
1

[root@master4 day3]# [ -f /etc/services ] && echo 1 || echo 0
1
[root@master4 day3]# [ -f /etc/rc.locl ] && echo 1 || echo 0
0
[root@master4 day3]#
[root@master4 day3]# [ -f /etc/rc.local ] && echo 1 || echo 0
1

How to use it? A: Look at the system script

If the execution is unsuccessful, execute the following
[ -x /usr/sbin/rpc.nfsd ] || exit 5

If the execution is successful, execute the following
[ -x /usr/sbin/rpc.nfsd ] && exit 5

2.1 Script Examples

3. Multi-condition file Test 3.1 example

[root@master4 day3]# [ -f $file1 -a -f $file2 ] && echo 1 || echo 0
1

[root@master4 day3]# [ -f $file1 -a -f ${file:-null} ] && echo 1 || echo 0
0

The effect of double quotes came out
[root@master4 day3]# [ -f "$file1" -a -f "$file" ] && echo 1 || echo 0
0
[root@master4 day3]# [ -f "$file1" -o -f "$file" ] && echo 1 || echo 0
1
[root@master4 day3]#

[root@master4 day3]# [ -f "$file1" -a -d "$file2" ] && echo 1 || echo 0
0

Summary:
1. "-A" and "-o" logic operators are used in [], syntax [$m-a $n]
2. "&&" and "| |" are used in [[]] to use [$m && $n]. If single brackets are used [] && []
3, note the brackets at both ends, must have a space

After the condition, you need to execute multiple statements, you need to use braces
[root@master4 day3]# vim test.sh

[ 3 -ne 3 ] || {
     Echo "I am oldboy"
     Echo "I am coming"
     Exit 1
}

If using one line, separate them with a semicolon:
[root@master4 day3]# [ 3 -ne 3 ] || { echo "I am oldboy";echo "I am coming";exit 1; }

4, String Test Example 4.1 example

Strings should be quoted [ -n "$file1" ]

[root@master4 day3]# echo $file2
/etc/rc.local
[root@master4 day3]# echo $file1
/etc/services
[root@master4 day3]# echo $file0

[root@master4 day3]# [ -n "$file" ] && echo 1 || echo 0
0

The content is empty and true:
[root@master4 day3]# [ -z "$file" ] && echo 1 || echo 0
1

[root@master4 day3]# [ -z "$file1" ] && echo 1 || echo 0
0
[root@master4 day3]# [ -n "$file1" ] && echo 1 || echo 0
1

summary:
     -z STRING string is empty
     -n STRING string is true if it is not empty

5. Multi-condition String Test 5.1 example

[root@master4 day3]# echo $file

[root@master4 day3]# echo $file1
/etc/services
[root@master4 day3]# echo $file2
/etc/rc.local

[root@master4 day3]# [ -n "$file1" -a -z "$file2" ] && echo 1 || echo 0
0

One is true, output 1
[root@master4 day3]# [[ -n "$file1" || -n "$file2" ]] && echo 1 || echo 0
1

[root@master4 day3]# [[ "$file1" = "$file2" ]] && echo 1 || echo 0
0
[root@master4 day3]#

[root@master4 day3]# [[ "$file1" != "$file2" ]] && echo 1 || echo 0
1

Compare length:
[root@master4 day3]# [[ "${#file1}" = "${#file2}" ]] && echo 1 || echo 0
1
[root@master4 day3]#

[root@master4 day3]# [[ "${#file1}" != "${#file2}" ]] && echo 1 || echo 0
0

summary:
String comparisons must be enclosed in double quotes.
[ -z "$file1" ]

[ "$file1" != "$file2" ]

6. Integer Test 6.1 Example

Do not add double quotes to integer comparisons

[root@master4 day3]# a1=10;a2=13
[root@master4 day3]# echo $a1 $a2
10 13

[root@master4 day3]# [ $a1 -eq $a2 ] && echo 1 || echo 0
0

[root@master4 day3]# [ $a1 -gt $a2 ] && echo 1 || echo 0
0
[root@master4 day3]#
[root@master4 day3]# [ $a1 -ge $a2 ] && echo 1 || echo 0
0
[root@master4 day3]#
[root@master4 day3]# [ $a1 -ne $a2 ] && echo 1 || echo 0
1
[root@master4 day3]# [ $a1 -le $a2 ] && echo 1 || echo 0
1

[root@master4 day3]# [[ $a1 -eq $a2 ]] && echo 1 || echo 0
0
[root@master4 day3]# [[ $a1 -gt $a2 ]] && echo 1 || echo 0
0
[root@master4 day3]# [[ $a1 -g\lt $a2 ]] && echo 1 || echo 0
[root@master4 day3]# [[ $a1 -lt $a2 ]] && echo 1 || echo 0
1

[root@master4 day3]# [[ $a1 = $a2 ]] && echo 1 || echo 0
0
[root@master4 day3]# [[ $a1 != $a2 ]] && echo 1 || echo 0
1
[root@master4 day3]# [[ $a1 > $a2 ]] && echo 1 || echo 0
0
[root@master4 day3]# [[ $a1 < $a2 ]] && echo 1 || echo 0
1

Double parenthesis comparison:
[root@master4 day3]# (( $a1 > $a2 )) && echo 1 || echo 0
0
[root@master4 day3]# (( $a1 < $a2 )) && echo 1 || echo 0
1

7. Test Command 7.1 Testing Example

[root@master4 day3]# test -z "$file1" && echo 1 || echo 0
0

[root@master4 day3]# test -n "$file1" && echo 1 || echo 0
1

[root@master4 day3]# test 3 -ne 3 || echo 0
0

[root@master4 day3]# test "dd" != "ff" || echo 0
[root@master4 day3]#

[root@master4 day3]# test "dd" != "dd" || echo 0
0

Test the test of the file:
[root@master4 day3]# test ! -f /etc/rc.local || echo 1
1

[root@master4 day3]# touch file1
[root@master4 day3]# touch file2
[root@master4 day3]#
[root@master4 day3]# [ file1 -nt file2 ] && echo 1 || echo 0
0
[root@master4 day3]# [ file1 -ot file2 ] && echo 1 || echo 0
1
[root@master4 day3]#

[root@master4 day3]# test file1 -ot file2 && echo 1 || echo 0
1

For the use of the operators of test,[],[[]], help test.

8. Logical operator Test 8.1 example

[root@master4 day3]# [ -f "$file1" -a "$file2" ] && echo 1 || echo 0
1

[root@master4 day3]# [ -f "$file1" -o "$file2" ] && echo 1 || echo 0
1

[root@master4 day3]# [ ! -f "$file1" -o ! "$file2" ] && echo 1 || echo 0
0

[root@master4 day3]# [ -f "$file1" -a -f "$file2" ] && echo 1 || echo 0
1
[root@master4 day3]# [ ! -f "$file1" -a -f "$file2" ] && echo 1 || echo 0
0

[root@master4 day3]# test ! -f "$file1" -a -f "$file2" && echo 1 || echo 0
0

[root@master4 day3]# test ! -f "$file1" && -f "$file23" && echo 1 || echo 0
0

[root@master4 day3]# test -f "$file1" && -o "$file2" && echo 1 || echo 0
-bash: -o: command not found
0
[root@master4 day3]# 
[root@master4 day3]# test -f "$file1" -o -f "$file2" && echo 1 || echo 0
1

Iv. Example 1, read print menu

[root@master4 day3]# cat test01.sh 
cat <<END
    1.DDD
    2.FFF
END
[root@master4 day3]# sh test01.sh 
    1.DDD
    2.FFF

1.1 menu.sh, print a simple menu

[root@master4 day3]# cat menu.sh
Menu(){
Cat <<END
    1.[install lamp]
    2.[install lnmp]
    3.[exit]
    Pls input the num you want:
END
}

Menu

Improve:
[root@master4 day3]# cat menu.sh
Menu(){
Cat <<END
    1.[install lamp]
    2.[install lnmp]
    3.[exit]
    Pls input the num you want:
END
}
Menu
Read num
Echo "you have selected $num"

test:
[root@master4 day3]# sh menu.sh
    1.[install lamp]
    2.[install lnmp]
    3.[exit]
    Pls input the num you want:
2
You have selected 2
[root@master4 day3]#

Continue to improve:
[root@master4 day3]# cat menu.sh
Menu(){
Cat <<END
    1.[install lamp]
    2.[install lnmp]
    3.[exit]
    Pls input the num you want:
END
}
Menu
Read num
Echo "you have selected $num"
[ $num -eq 1 ] && {
    Echo "starting install lamp"
    #/bin/sh /server/scripts/lamp.sh
    Exit
}

[ $num -eq 2 ] && {
    Echo "staring install lnmp"
    #/bin/sh /server/scripts/lnmp.sh
    Exit
}

[ $num -eq 3 ] && {
    Echo "this scripts logout."
    Exit
}

[ ! $num -eq 1 -o ! $num -eq 2 -o ! $num -eq 3 ] &&{
    Echo "bye"
    Exit 1
}

1.2 Multi-level menu

[root@master4 day3]# cat menu1.sh
Menu1(){
Cat <<END
    ********************************
    1.[install lamp]
    2.[install lnmp]
    3.[exit]
    Pls input the num you want:
   *********************************
END
}

Menu2(){
Cat <<END
    ==================================
    1.[install apache]
    2.[install php]
    3.[instal mysql]
    4.[back]
    Pls input the num you want:
    ==================================
END
}

Menu1
Read -p "you input the num is:" num
[ $num -eq 1 ] && {
    Menu2
    Read -p "you input the num is:" num2
    [ $num2 -eq 1 ] && {
    Echo "start installing apache."
    Exit
    }
}

test:
[root@master4 day3]# sh menu1.sh
    ********************************
    1.[install lamp]
    2.[install lnmp]
    3.[exit]
    Pls input the num you want:
   *********************************
You input the num is:1
    ==================================
    1.[install apache]
    2.[install php]
    3.[instal mysql]
    4.[back]
    Pls input the num you want:
    ==================================
You input the num is:1
Start installing apache.

Shell Learning Notes (2)

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