Use of shell scripts---if condition judgment

Testing and judging of shell scripts

1. Testing

Grammar:

[operator condition] = = Test operator condition

1) test file-level directory

Type of File:

F, File

Ls-l # #只查看字段的第一个字符, file "-"

D, Catalogue

Ls-ld

L, Link file

Ls-l

C, character device

Ls-l/dev/tty

B, block device

Ls-l/dev/sda1

s, socket file, General Service using MySQL

Ls-l/tmp/mysql.socket

P, Pipe

Mkfifo hehe # #创建管道文件

Ls-l hehe

Test operator:-f file,-D directory, whether E exists,-R is readable,-w is writable,-X is executable

Case LIST:

[-d/tmp]

echo $? # #返回值为0代表/tmp is a directory

2) Comparison of integers

Operator:

-eq equals,-ne not equal to,-gt greater than,-lt, less than, ge greater than equals, le less than equals

Case LIST:

[10-gt 11]

[$?-eq 0] # #上一条命令是否执行成功

3) string comparison

String: Refers to a data type that can be interpreted as plain text type

Operator: = = is equal,! = is not equal,-Z is empty

Case LIST:

Str1=hehe

[$STR 1 = = hehe]

[$LANG = = en]

[$STR 1! = linuxfan.cn]

str2= # #直接回车

[-Z $STR 2]

[-Z $ "/root/a"] # #这个文件是否为空

4) Logical Judgment

Logical judgment is the same as or non-

Grammar:

[Expression 1] && (and), | | (OR),! (non) [expression 2]

Case LIST:

Compiling the installation

./configure &&make &&make

[1–ge 2] | | [1–lt 2] # #测试结果为真

[$LANG! = en]

2. If judgment

1) Single Branch

Grammar:

if [Condition];then

Command

Fi

Case: Determine if the LFTP is installed if not installed

VI install_lftp.sh

#!/bin/bash

Rpm-qa |grep lftp 1>/dev/null

If [$?-ne 0];then # #若上调命令执性不成功说明没有安装lftp, install

Yum-y Install lftp &>/dev/null &&echo "lftp installed."

Fi

: Wq

2) if dual branch

Grammar:

if [Condition];then

Command

Else

Command 1

Fi

Use single-branch case script overwrite if installed and put back already installed, not installed

3) If multi-branch

Grammar:

if [Condition 1];then

Command 1

elif [Condition 2];then

Command 2

...

else [Condition 3];then

Command

Fi

Case LIST:

VI s60.sh

#!/bin/bash

Ls/etc/rc.d/rc3.d/s60vsftpd

If [$?-ne 0]

Then

Chkconfig vsftpd on

elif [-X/ETC/INIT.D/VSFTPD]

Then

chmod +x/etc/init.d/vsftpd

Else

/ETC/INIT.D/VSFTPD restart

Fi

: Wq

Consolidated Case List

VI if_then_fi.sh

#!/bin/bash

name=$ (basename)

If [$#-ne 2-a $#-ne 3];then

echo "Usage: $name vaule1 value2"

echo "$name value1 value2 vaule3"

Exit 1

Fi

If [$#-eq 2];then

echo "Args:$1,$2"

Else

echo "Three args:$1,$2,$3"

Fi

If [$#-eq 2];then

If [$1-gt $];then

echo "$ > $"

elif [$1-lt $];then

echo "$ < $"

Else

echo "$ = $"

Fi

Else

If [$1-ge $2-a $1-ge $];then

echo "$ >=$2,$1 >=$3"

elif [$1-ge $2-a $1-le $];then

echo "$ >=$2,$1 <="

elif [$1-lt $2-a $1-ge $];then

echo "$ < $2,$1 >="

Else

echo "$ < $2,$1 < $"

Fi

Fi

Exit 0

: Wq

This article from "Lp-linux" blog, declined reprint!

Use of shell scripts---if condition judgment