if语句和case语句用法展示
SHELL脚本编程条件选择(if语句)和条件判断(case语句)
作者：尹正杰
版权声明：原创作品，谢绝转载！否则将追究法律责任。
一.条件选择if语句
[root@node101.yinzhengjie.org.cn ~]# help if
if: if COMMANDS; then COMMANDS; [ elif COMMANDS; then COMMANDS; ]... [ else COMMANDS; ] fi
Execute commands based on conditional. The `if COMMANDS' list is executed. If its exit status is zero, then the
`then COMMANDS' list is executed. Otherwise, each `elif COMMANDS' list is
executed in turn, and if its exit status is zero, the corresponding
`then COMMANDS' list is executed and the if command completes. Otherwise,
the `else COMMANDS' list is executed, if present. The exit status of the
entire construct is the exit status of the last command executed, or zero
if no condition tested true. Exit Status:
Returns the status of the last command executed.
[root@node101.yinzhengjie.org.cn ~]#
[root@node101.yinzhengjie.org.cn ~]#
[root@node101.yinzhengjie.org.cn ~]# help if #查看if语句的帮助信息
1>.单分支if语句
语法格式一(推荐)
if [ 条件测试表达式 ];then
源代码
fi 语法格式二
if [ 条件测试表达式 ]
then
源代码
fi 温馨提示:
条件选择语句顾名思义就是根据条件测试表达式是否为true选择执行。
if语句可嵌套。
if语句使用fi结尾，和一般语言使用大括号结尾不同；
[ 条件测试表达式 ]就是使用test命令测试，所以中括号和条件判断式之间必须有空格；
then后面跟符合条件之后执行的程序，可以放在[]之后，用";"分割。也可以换行写入，就不需要";"啦；
[root@node101.yinzhengjie.org.cn ~]# vim shell/partitions.sh #编写一个监控boot分区的脚本
[root@node101.yinzhengjie.org.cn ~]#
[root@node101.yinzhengjie.org.cn ~]# cat shell/partitions.sh
#!/bin/bash
#
#********************************************************************
#Author: yinzhengjie
#QQ:
#Date: --
#FileName： shell/partitions.sh
#URL: http://www.cnblogs.com/yinzhengjie
#Description： The test script
#Copyright notice: original works, no reprint! Otherwise, legal liability will be investigated.
#******************************************************************** res=$(df -h | grep "/dev/sda1" | awk '{print $5}'| cut -d "%" -f1) if [ $res -ge ]
then
echo "Warning! /dev/sda2 is full!!!"
fi
[root@node101.yinzhengjie.org.cn ~]#
[root@node101.yinzhengjie.org.cn ~]# chmod +x shell/partitions.sh
[root@node101.yinzhengjie.org.cn ~]#
[root@node101.yinzhengjie.org.cn ~]# ll shell/partitions.sh
-rwxr-xr-x root root Nov : shell/partitions.sh
[root@node101.yinzhengjie.org.cn ~]#
[root@node101.yinzhengjie.org.cn ~]# df -h
Filesystem Size Used Avail Use% Mounted on
/dev/mapper/centos-root 50G .5G 49G % /
devtmpfs .9G .9G % /dev
tmpfs .9G .9G % /dev/shm
tmpfs .9G 8.6M .9G % /run
tmpfs .9G .9G % /sys/fs/cgroup
/dev/sda1 1014M 146M 869M % /boot
/dev/mapper/centos-home 941G .0G 938G % /home
tmpfs 783M 783M % /run/user/
[root@node101.yinzhengjie.org.cn ~]#
[root@node101.yinzhengjie.org.cn ~]# ./shell/partitions.sh
[root@node101.yinzhengjie.org.cn ~]#
[root@node101.yinzhengjie.org.cn ~]# dd if=/dev/zero of=/boot/bigfile bs=1M count= #为了达到测试效果，为我们可以把在"/boot"分区里写入一个大文件从而达到快速达到脚本报警阈值。
+ records in
+ records out
bytes ( MB) copied, 1.78826 s, MB/s
[root@node101.yinzhengjie.org.cn ~]#
[root@node101.yinzhengjie.org.cn ~]# df -h
Filesystem Size Used Avail Use% Mounted on
/dev/mapper/centos-root 50G .5G 49G % /
devtmpfs .9G .9G % /dev
tmpfs .9G .9G % /dev/shm
tmpfs .9G 8.6M .9G % /run
tmpfs .9G .9G % /sys/fs/cgroup
/dev/sda1 1014M 948M 67M % /boot
/dev/mapper/centos-home 941G .0G 938G % /home
tmpfs 783M 783M % /run/user/
[root@node101.yinzhengjie.org.cn ~]#
[root@node101.yinzhengjie.org.cn ~]# ./shell/partitions.sh
Warning! /dev/sda2 is full!!!
[root@node101.yinzhengjie.org.cn ~]#
[root@node101.yinzhengjie.org.cn ~]# vim shell/partitions.sh #编写一个监控boot分区的脚本
[root@node101.yinzhengjie.org.cn ~]# declare -f | grep if #不难发现系统中定义的脚本也有很多if嵌套使用案例
if [[ ${!} == \~* ]]; then
if [[ ${!} == */* ]]; then
if [[ $index -gt 0 && ( -n $lead && -n ${lead//[[:space:]]} ) ]]; then
if [[ $i -lt $cword ]]; then
if [[ "$1" == *:* && "$COMP_WORDBREAKS" == *:* ]]; then
if [[ $option =~ (\[((no|dont)-?)\]). ]]; then
if [[ -n $1 ]]; then
if [[ -n $exclude ]]; then
if _complete_as_root; then
if _complete_as_root; then
if [[ ${1:-} == -w ]]; then
if [[ ${1:-} == -a ]]; then
cmd="{ ifconfig || ip link show up; }";
cmd="{ ifconfig -a || ip link show; }";
COMPREPLY=($( eval $cmd 2>/dev/null | awk '/^[^ \t]/ { if ($1 ~ /^[0-9]+:/) { print $2 } else { prin
t $1 } }' )); if [[ -z "${CDPATH:-}" || "$cur" == ?(.)?(.)/* ]]; then
if [[ ( -n $mark_symdirs && -h $j || -n $mark_dirs && ! -h $j ) && ! -d ${j#$i/} ]]; then
if [[ ${#COMPREPLY[@]} -eq 1 ]]; then
if [[ "$i" == "$cur" && $i != "*/" ]]; then
if [[ "${COMP_WORDS[i]}" != -* ]]; then
if [[ $COMP_CWORD -eq ]]; then
if [[ ! -n $cspec && $cmd == */* ]]; then
if [[ ! -n $cspec ]]; then
if [[ -n $cspec ]]; then
if [[ ${cspec#* -F } != $cspec ]]; then
if [[ ${#COMP_WORDS[@]} -ge 2 ]]; then
if [[ ${#COMPREPLY[@]} -eq 0 ]]; then
if [[ -f /etc/debian_version ]]; then
COMPREPLY=($( compgen -W "$( sed -ne 's|^iface \([^ ]\{1,\}\).*$|\1|p' /etc/network/interface
s )" -- "$cur" )); if [[ -f /etc/SuSE-release ]]; then
COMPREPLY=($( compgen -W "$( printf '%s\n' /etc/sysconfig/network/ifcfg-* |
sed -ne 's|.*ifcfg-\(.*\)|\1|p' )" -- "$cur" )); if [[ -f /etc/pld-release ]]; then
COMPREPLY=($( compgen -W "$( command ls -B /etc/sysconfig/interfaces | s
ed -ne 's|.*ifcfg-\(.*\)|\1|p' )" -- "$cur" )); COMPREPLY=($( compgen -W "$( printf '%s\n' /etc/sysconfig/network-scripts/ifcfg-* |
sed -ne 's|.*ifcfg-\(.*\)|\1|p' )" -- "$cur" )); if [[ "$cur" == \~*/* ]]; then
if [[ "$cur" == \~* ]]; then
if [[ "$1" != -d ]]; then
if [[ ${#toks[@]} -ne ]]; then
if [[ $xspec == !* ]]; then
if [[ ${#toks[@]} -ne ]]; then
if [[ -e /proc/filesystems ]]; then
if [[ -n ${//[^0-9]/} ]]; then
if [[ "${#words[cword]}" -eq || "$COMP_POINT" == "${#COMP_LINE}" ]]; then
if [[ "$i" -lt "$cword" ]]; then
if [[ "${words[cword]:0:${#cur}}" != "$cur" ]]; then
if [[ "${COMP_WORDS[i]}" != -* ]]; then
if [[ $COMP_CWORD -ge ]]; then
if type getent &>/dev/null; then
if type perl &>/dev/null; then
if [[ $cur == $redir* || $prev == $redir ]]; then
if [[ ${words[i]} == $redir* ]]; then
COMPREPLY=($( compgen -W "$( PATH="$PATH:/sbin" lsmod | awk '{if (NR != 1) print $1}' )" -- "$1" ))
COMPREPLY+=($( compgen -W "$( { LC_ALL=C ifconfig -a || ip addr show; } 2>/dev/null |
[[ $# -ge $OPTIND ]] && echo "error: $FUNCNAME("$@"): unprocessed arguments:" $(while [[ $# -ge $OPTIND ]];
do printf '%s\n' ${!OPTIND}; shift; done); if [[ -n $configfile ]]; then
if [[ ${#config[@]} -gt ]]; then
if [[ -z $configfile ]]; then
if [[ ${#kh[@]} -gt || ${#khd[@]} -gt ]]; then
if [[ "$awkcur" == [-]*[.:]* ]]; then
if [[ "$awkcur" == [-]* ]]; then
if [[ -z $awkcur ]]; then
if [[ ${#kh[@]} -gt ]]; then
if ($i !~ /[*?]/ && $i ~ /'"$awkcur"'/) {print $i} \
if [[ ${#khd[@]} -gt ]]; then
if [[ "$i" == *key_22_$curd*.pub && -r "$i" ]]; then
if [[ ${#config[@]} -gt && -n "$aliases" ]]; then
if [[ -n ${COMP_KNOWN_HOSTS_WITH_AVAHI:-} ]] && type avahi-browse &>/dev/null; then
if [[ -n ${COMP_KNOWN_HOSTS_WITH_HOSTFILE-} ]]; then
if [[ "$cur" == -* ]]; then
if [[ "$1" == @(mk|rm)dir ]]; then
COMPREPLY+=($( { ifconfig -a || ip link show; } >/dev/null | sed -ne "s/.*[[:space:]]HWaddr[[:space
:]]\{,\}\($re\)[[:space:]].*/\/p" -ne "s/.*[[:space:]]HWaddr[[:space:]]\{,\}\($re\)[[:space:]]*$/\/p" -ne "s|.*[[:space:]]\(link/\)\{,\}ether[[:space:]]\{,\}\($re\)[[:space:]].*|\|p" -ne "s|.*[[:space:]]\(link/\)\{,\}ether[[:space:]]\{,\}\($re\)[[:space:]]*$|\|p" if [[ $1 == \'* ]]; then
if type -p realpath > /dev/null; then
if type -p greadlink > /dev/null; then
if type -p readlink > /dev/null; then
if [[ $cword -eq && $prev == ?(*/)service ]]; then
if [[ "$cur" == --?*=* ]]; then
if [[ $ == \~* && $ != */* ]]; then
if type getent &>/dev/null; then
if type perl &>/dev/null; then
if unset -v "$1"; then
if (( $# == 2 )); then
if ! (( $# )); then
echo "bash: ${FUNCNAME[0]}: \`$1': missing" "number specifier" 1>&2;
echo "bash:" "${FUNCNAME[0]}: \`$1': invalid number specifier" 1>&2;
[[ -n "$2" ]] && unset -v "$2" && eval $2=\(\"\${@:3:${1#-a}}\"\) && shift $((${1#-a} + 2)) || {
[[ -n "$2" ]] && unset -v "$2" && eval $2=\"\$3\" && shift 3 || {
if [[ $cur == *@* ]]; then
if [[ $cur = *\\\\* || $cur = *:*:* ]]; then
if [[ $cur = *\\:* ]]; then
if [[ $1 == -u ]]; then
if [[ $cur = *:* ]]; then
if [[ $1 == -u ]]; then
if [[ $1 == -u ]]; then
if [[ $cur =~ ^(\$\{?)([A-Za-z0-9_]*)$ ]]; then
shift;
if [[ -d $xinetddir ]]; then
[root@node101.yinzhengjie.org.cn ~]#
[root@node101.yinzhengjie.org.cn ~]#
[root@node101.yinzhengjie.org.cn ~]# declare -f | grep if #不难发现系统中定义的脚本也有很多if嵌套使用案例
2>.双分支if语句
if [ 条件测试表达式 ]
then
条件成立时，执行的源代码。
else
条件不成立时，执行的另一个程序。
fi
[root@node101.yinzhengjie.org.cn ~]# vim shell/file_backup.sh #备份服务器的某个目录
[root@node101.yinzhengjie.org.cn ~]#
[root@node101.yinzhengjie.org.cn ~]# ll
total
drwxr-xr-x root root Nov : shell
[root@node101.yinzhengjie.org.cn ~]#
[root@node101.yinzhengjie.org.cn ~]# cat shell/file_backup.sh
#!/bin/bash
#
#********************************************************************
#Author: yinzhengjie
#QQ:
#Date: --
#FileName： shell/file_backup.sh
#URL: http://www.cnblogs.com/yinzhengjie
#Description： The test script
#Copyright notice: original works, no reprint! Otherwise, legal liability will be investigated.
#******************************************************************** #同步系统时间，可以先ping通再选择服务器，.cn.pool.ntp.org；.asia.pool.ntp.org；.asia.pool.ntp.org
ntpdate .asia.pool.ntp.org &> /dev/null FilePath="/boot"
BackSave="/root/backup"
date=`date +%F`
size=$(du -sh $FilePath) filename=boot_${date}.tar.gz if [ -d $BackSave ]
then
usleep
else
mkdir $BackSave
fi echo "Date is:$date" > ${BackSave}/backup.log
echo "Size is:$size" >> ${BackSave}/backup.log
tar -zcf ${BackSave}/${filename} ${FilePath} ${BackSave}/backup.log &> /dev/null
rm -f ${BackSave}/backup.log
[root@node101.yinzhengjie.org.cn ~]#
[root@node101.yinzhengjie.org.cn ~]# bash shell/file_backup.sh
[root@node101.yinzhengjie.org.cn ~]#
[root@node101.yinzhengjie.org.cn ~]# ll
total
drwxr-xr-x root root Nov : backup
drwxr-xr-x root root Nov : shell
[root@node101.yinzhengjie.org.cn ~]#
[root@node101.yinzhengjie.org.cn ~]# cd backup/
[root@node101.yinzhengjie.org.cn ~/backup]#
[root@node101.yinzhengjie.org.cn ~/backup]# ll
total
-rw-r--r-- root root Nov : boot_2019--.tar.gz
[root@node101.yinzhengjie.org.cn ~/backup]#
[root@node101.yinzhengjie.org.cn ~/backup]# tar zxf boot_2019--.tar.gz
[root@node101.yinzhengjie.org.cn ~/backup]# ll
total
dr-xr-xr-x root root Nov : boot
-rw-r--r-- root root Nov : boot_2019--.tar.gz
drwxr-xr-x root root Nov : root
[root@node101.yinzhengjie.org.cn ~/backup]#
[root@node101.yinzhengjie.org.cn ~/backup]# cat root/backup/backup.log
Date is:--
Size is:113M /boot
[root@node101.yinzhengjie.org.cn ~/backup]#
[root@node101.yinzhengjie.org.cn ~/backup]# ll boot
total
-rw-r--r-- root root Nov config-3.10.-.el7.x86_64
drwxr-xr-x root root Jul : efi
drwxr-xr-x root root Jul : grub
drwx------ root root Jul : grub2
-rw------- root root Jul : initramfs--rescue-9ccdf621e5984f3b8626614f6fa15a48.img
-rw------- root root Jul : initramfs-3.10.-.el7.x86_64.img
-rw------- root root Jul : initramfs-3.10.-.el7.x86_64kdump.img
-rw-r--r-- root root Nov symvers-3.10.-.el7.x86_64.gz
-rw------- root root Nov System.map-3.10.-.el7.x86_64
-rwxr-xr-x root root Jul : vmlinuz--rescue-9ccdf621e5984f3b8626614f6fa15a48
-rwxr-xr-x root root Nov vmlinuz-3.10.-.el7.x86_64
[root@node101.yinzhengjie.org.cn ~/backup]#
[root@node101.yinzhengjie.org.cn ~]# vim shell/file_backup.sh #备份服务器的某个目录
[root@node101.yinzhengjie.org.cn ~]# vim shell/server_alarm.sh #判断某个服务是否启动
[root@node101.yinzhengjie.org.cn ~]#
[root@node101.yinzhengjie.org.cn ~]# cat shell/server_alarm.sh
#!/bin/bash
#
#********************************************************************
#Author: yinzhengjie
#QQ:
#Date: --
#FileName： shell/server_alarm.sh
#URL: http://www.cnblogs.com/yinzhengjie
#Description： The test script
#Copyright notice: original works, no reprint! Otherwise, legal liability will be investigated.
#******************************************************************** Host=127.0.0.1 res=`rpm -qa | grep nmap | head -` if [ -z $res ]
then
yum -y install nmap &> /dev/null
else
echo “准备开始扫描主机服务！”
fi ServiceStatus=$(nmap -sT $Host |grep tcp | grep http|awk '{print $2}') #使用nmap可以准确的判断一台服务器的服务是否正常。 if [ "$ServiceStatus" == "open" ]
then
echo "$(date) httpd is ok !" >> /tmp/HttpdAlarm-acc.log
else
systemctl restart httpd &>/dev/null #注意，如果不是你本机的话，不能直接这么干哟，需要先远程上去再执行命令！
echo "`date` restart httpd!!" >> /tmp/HttpdAlarm-err.log
fi
[root@node101.yinzhengjie.org.cn ~]#
[root@node101.yinzhengjie.org.cn ~]# ss -ntl
State Recv-Q Send-Q Local Address:Port Peer Address:Port
LISTEN *: *:*
LISTEN ::: :::*
[root@node101.yinzhengjie.org.cn ~]#
[root@node101.yinzhengjie.org.cn ~]# bash shell/server_alarm.sh
“准备开始扫描主机服务！”
[root@node101.yinzhengjie.org.cn ~]#
[root@node101.yinzhengjie.org.cn ~]# ss -ntl
State Recv-Q Send-Q Local Address:Port Peer Address:Port
LISTEN *: *:*
LISTEN *: *:*
LISTEN ::: :::*
[root@node101.yinzhengjie.org.cn ~]#
[root@node101.yinzhengjie.org.cn ~]# cat /tmp/HttpdAlarm-err.log
Sat Nov :: CST restart httpd!!
[root@node101.yinzhengjie.org.cn ~]#
[root@node101.yinzhengjie.org.cn ~]# bash shell/server_alarm.sh
“准备开始扫描主机服务！”
[root@node101.yinzhengjie.org.cn ~]#
[root@node101.yinzhengjie.org.cn ~]# cat /tmp/HttpdAlarm-acc.log
Sat Nov :: CST httpd is ok !
[root@node101.yinzhengjie.org.cn ~]#
[root@node101.yinzhengjie.org.cn ~]#
[root@node101.yinzhengjie.org.cn ~]# vim shell/server_alarm.sh #判断某个服务是否启动
[root@node101.yinzhengjie.org.cn ~]# vim shell/ip_judge.sh #判断IP是否合法
[root@node101.yinzhengjie.org.cn ~]#
[root@node101.yinzhengjie.org.cn ~]# cat shell/ip_judge.sh
#!/bin/bash
#
#********************************************************************
#Author: yinzhengjie
#QQ:
#Date: --
#FileName： shell/ip_judge.sh
#URL: http://www.cnblogs.com/yinzhengjie
#Description： The test script
#Copyright notice: original works, no reprint! Otherwise, legal liability will be investigated.
#******************************************************************** read -p "Please input a ip address >>>: " IP
if [[ "$IP" =~ ^(([-]?[-]|[-]{}|[-][-]|[-])\.){}([-]?[-]|[-]{}|[-][-]|[-])$ ]]
then
echo "$IP is legal"
else
echo "$IP is illegal" [root@node101.yinzhengjie.org.cn ~]#
[root@node101.yinzhengjie.org.cn ~]# bash shell/ip_judge.sh
Please input a ip address >>>: 127.0.0.1
shell/ip_judge.sh: line : syntax error: unexpected end of file
[root@node101.yinzhengjie.org.cn ~]#
[root@node101.yinzhengjie.org.cn ~]# vim shell/ip_judge.sh
[root@node101.yinzhengjie.org.cn ~]# cat shell/ip_judge.sh
#!/bin/bash
#
#********************************************************************
#Author: yinzhengjie
#QQ:
#Date: --
#FileName： shell/ip_judge.sh
#URL: http://www.cnblogs.com/yinzhengjie
#Description： The test script
#Copyright notice: original works, no reprint! Otherwise, legal liability will be investigated.
#******************************************************************** read -p "Please input a ip address >>>: " IP
if [[ "$IP" =~ ^(([-]?[-]|[-]{}|[-][-]|[-])\.){}([-]?[-]|[-]{}|[-][-]|[-])$ ]]
then
echo "$IP is legal"
else
echo "$IP is illegal"
fi [root@node101.yinzhengjie.org.cn ~]# bash shell/ip_judge.sh
Please input a ip address >>>: 127.0.0.1
127.0.0.1 is legal
[root@node101.yinzhengjie.org.cn ~]# bash shell/ip_judge.sh
Please input a ip address >>>: 172.30.1.101
172.30.1.101 is legal
[root@node101.yinzhengjie.org.cn ~]# bash shell/ip_judge.sh
Please input a ip address >>>: 192.168.100.1
192.168.100.1 is legal
[root@node101.yinzhengjie.org.cn ~]#
[root@node101.yinzhengjie.org.cn ~]# bash shell/ip_judge.sh
Please input a ip address >>>: 256.256.256.256
256.256.256.256 is illegal
[root@node101.yinzhengjie.org.cn ~]#
[root@node101.yinzhengjie.org.cn ~]# bash shell/ip_judge.sh
Please input a ip address >>>: 255.255.255.255
255.255.255.255 is legal
[root@node101.yinzhengjie.org.cn ~]# bash shell/ip_judge.sh
Please input a ip address >>>:
is illegal
[root@node101.yinzhengjie.org.cn ~]#
[root@node101.yinzhengjie.org.cn ~]# vim shell/ip_judge.sh #判断IP是否合法
[root@node101.yinzhengjie.org.cn ~]# vim shell/createuser.sh #编写创建脚本的案例
[root@node101.yinzhengjie.org.cn ~]# cat shell/createuser.sh
#!/bin/bash
#
#********************************************************************
#Author: yinzhengjie
#QQ:
#Date: --
#FileName： shell/createuser.sh
#URL: http://www.cnblogs.com/yinzhengjie
#Description： The test script
#Copyright notice: original works, no reprint! Otherwise, legal liability will be investigated.
#******************************************************************** if [ -z "$1" ];then
read -p "Please input a username >>>: " USER
if [ -z "$USER" ];then
echo "INPUT FLASE"
exit
else
USERNAME=$USER
fi
else
USERNAME=$
fi if id $USERNAME &> /dev/null;then
echo "$USERNAME is exist"
exit
else
useradd $USERNAME && echo "$USERNAME is created"
echo "yinzhengjie" | passwd --stdin $USERNAME &> /dev/null && echo "$USERNAME defalut password: yinzhengjie"
passwd -e $USERNAME
echo userinfo: `id $USERNAME`
fi
[root@node101.yinzhengjie.org.cn ~]# bash -n shell/createuser.sh
[root@node101.yinzhengjie.org.cn ~]# bash shell/createuser.sh
Please input a username >>>: root
root is exist
[root@node101.yinzhengjie.org.cn ~]#
[root@node101.yinzhengjie.org.cn ~]# bash shell/createuser.sh
Please input a username >>>: yinzhengjie
yinzhengjie is exist
[root@node101.yinzhengjie.org.cn ~]#
[root@node101.yinzhengjie.org.cn ~]# bash shell/createuser.sh
Please input a username >>>: jason
jason is created
jason defalut password: yinzhengjie
Expiring password for user jason.
passwd: Success
userinfo: uid=(jason) gid=(jason) groups=(jason)
[root@node101.yinzhengjie.org.cn ~]#
[root@node101.yinzhengjie.org.cn ~]# id jason
uid=(jason) gid=(jason) groups=(jason)
[root@node101.yinzhengjie.org.cn ~]#
[root@node101.yinzhengjie.org.cn ~]#
[root@node101.yinzhengjie.org.cn ~]# vim shell/createuser.sh #编写创建脚本的案例
3>.多分支if语句
if [ 条件判断式1 ]
then
当条件判断式1成立时，执行的程序1
elif [ 条件判断式2 ]
then
当条件判断式2成立时，执行程序2
else
当所有条件都不成立时，最后执行此程序
fi 温馨提示:
逐条件进行判断，第一次遇为“真”条件时，执行其分支，而后结束整个if语句
[root@node101.yinzhengjie.org.cn ~]# cat shell/judge_filetype.sh #判断用户输入的文件类型
#!/bin/bash
#
#********************************************************************
#Author: yinzhengjie
#QQ:
#Date: --
#FileName： shell/judge_filetype.sh
#URL: http://www.cnblogs.com/yinzhengjie
#Description： The test script
#Copyright notice: original works, no reprint! Otherwise, legal liability will be investigated.
#******************************************************************** read -p "Please input a filename:" file if [ -z "$file" ]
then
echo "Eorr,please input a filename!"
exit
elif [ ! -e "$file" ]
then
echo "Your input is not a file!"
elif [ -f "$file" ]
then
echo "$file is a regulare file!"
elif [ -d "$file" ]
then
echo "$file is direcory!"
else
echo "$file is an other file!"
fi
[root@node101.yinzhengjie.org.cn ~]#
[root@node101.yinzhengjie.org.cn ~]# bash shell/judge_filetype.sh
Please input a filename:/etc/passwd
/etc/passwd is a regulare file!
[root@node101.yinzhengjie.org.cn ~]#
[root@node101.yinzhengjie.org.cn ~]# bash shell/judge_filetype.sh
Please input a filename:/root
/root is direcory!
[root@node101.yinzhengjie.org.cn ~]#
[root@node101.yinzhengjie.org.cn ~]# bash shell/judge_filetype.sh
Please input a filename:/root2
Your input is not a file!
[root@node101.yinzhengjie.org.cn ~]#
[root@node101.yinzhengjie.org.cn ~]#
[root@node101.yinzhengjie.org.cn ~]# cat shell/judge_filetype.sh #判断用户输入的文件类型
[root@node101.yinzhengjie.org.cn ~]# vim shell/song_of_five_rings.sh #五环之歌小脚本
[root@node101.yinzhengjie.org.cn ~]#
[root@node101.yinzhengjie.org.cn ~]# cat shell/song_of_five_rings.sh
#!/bin/bash
#
#********************************************************************
#Author: yinzhengjie
#QQ:
#Date: --
#FileName： shell/song_of_five_rings.sh
#URL: http://www.cnblogs.com/yinzhengjie
#Description： The test script
#Copyright notice: original works, no reprint! Otherwise, legal liability will be investigated.
#******************************************************************** read -p "Please input your site >>>: " NUM
[[ ! "$NUM" =~ ^[-]+$ ]] && { echo "Please input a digit";exit ;}
if [ "$NUM" -gt ];then
echo "Input false,please a [1-6] interger"
exit
elif [ "$NUM" -eq ];then
echo "more 1 circle than 5"
elif [ "$NUM" -eq ];then
echo "song of five rings"
elif [ "$NUM" -eq ];then
echo "less 1 circle than 5"
elif [ "$NUM" -eq ];then
echo "less 2 circle than 5"
elif [ "$NUM" -eq ];then
echo "less 3 circle than 5"
else
echo "二环是马路,一环是紫禁城!"
fi
[root@node101.yinzhengjie.org.cn ~]#
[root@node101.yinzhengjie.org.cn ~]# bash shell/song_of_five_rings.sh
Please input your site >>>:
Input false,please a [-] interger
[root@node101.yinzhengjie.org.cn ~]# bash shell/song_of_five_rings.sh
Please input your site >>>:
Input false,please a [-] interger
[root@node101.yinzhengjie.org.cn ~]#
[root@node101.yinzhengjie.org.cn ~]# bash shell/song_of_five_rings.sh
Please input your site >>>:
二环是马路,一环是紫禁城!
[root@node101.yinzhengjie.org.cn ~]# bash shell/song_of_five_rings.sh
Please input your site >>>:
less circle than
[root@node101.yinzhengjie.org.cn ~]# bash shell/song_of_five_rings.sh
Please input your site >>>:
less circle than
[root@node101.yinzhengjie.org.cn ~]# bash shell/song_of_five_rings.sh
Please input your site >>>:
less circle than
[root@node101.yinzhengjie.org.cn ~]# bash shell/song_of_five_rings.sh
Please input your site >>>:
song of five rings
[root@node101.yinzhengjie.org.cn ~]#
[root@node101.yinzhengjie.org.cn ~]#
[root@node101.yinzhengjie.org.cn ~]# vim shell/song_of_five_rings.sh #五环之歌小脚本
[root@node101.yinzhengjie.org.cn ~]# vim shell/yes_or_no.sh #判断用户输入yes或no
[root@node101.yinzhengjie.org.cn ~]#
[root@node101.yinzhengjie.org.cn ~]# cat shell/yes_or_no.sh
#!/bin/bash
#
#********************************************************************
#Author: yinzhengjie
#QQ:
#Date: --
#FileName： shell/yes_or_no.sh
#URL: http://www.cnblogs.com/yinzhengjie
#Description： The test script
#Copyright notice: original works, no reprint! Otherwise, legal liability will be investigated.
#******************************************************************** read -p "Do you agree?(yes or no)" ANSWER #将用户输入的字母统一转换成小写
lower_answer=`echo $ANSWER | tr 'A-Z' 'a-z'` if [ $lower_answer = "yes" -o $lower_answer = "y" ];then
echo YES
elif [ $lower_answer = "no" -o $lower_answer = "n" ];then
echo NO
else
echo "INPUT FALSE!"
fi
[root@node101.yinzhengjie.org.cn ~]#
[root@node101.yinzhengjie.org.cn ~]# bash shell/yes_or_no.sh
Do you agree?(yes or no)y
YES
[root@node101.yinzhengjie.org.cn ~]# bash shell/yes_or_no.sh
Do you agree?(yes or no)yes
YES
[root@node101.yinzhengjie.org.cn ~]# bash shell/yes_or_no.sh
Do you agree?(yes or no)no
NO
[root@node101.yinzhengjie.org.cn ~]# bash shell/yes_or_no.sh
Do you agree?(yes or no)n
NO
[root@node101.yinzhengjie.org.cn ~]#
[root@node101.yinzhengjie.org.cn ~]# bash shell/yes_or_no.sh
Do you agree?(yes or no)yesno
INPUT FALSE!
[root@node101.yinzhengjie.org.cn ~]#
[root@node101.yinzhengjie.org.cn ~]# vim shell/yes_or_no.sh #判断用户输入yes或no
[root@node101.yinzhengjie.org.cn ~]# vim shell/score.sh #根据分数来判断绩效
[root@node101.yinzhengjie.org.cn ~]#
[root@node101.yinzhengjie.org.cn ~]# cat shell/score.sh
#!/bin/bash
#
#********************************************************************
#Author: yinzhengjie
#QQ:
#Date: --
#FileName： shell/score.sh
#URL: http://www.cnblogs.com/yinzhengjie
#Description： The test script
#Copyright notice: original works, no reprint! Otherwise, legal liability will be investigated.
#******************************************************************** read -p "Please input your score: " score if [[ ! "$score" =~ ^[-]+$ ]];then
echo "Please input digit"
exit
elif [ "$score" -gt ];then
echo "Your score is invalid!"
exit
elif [ "$score" -lt ];then
echo "绩效为D,不及格"
elif [ "$score" -lt ];then
echo "绩效为C,继续努力"
elif [ "$score" -lt ];then
echo "绩效为B,超出任务预期"
elif [ "$score" -lt ];then
echo "绩效为A,优秀员工"
else
echo "绩效为S,公司骨干人员"
fi
[root@node101.yinzhengjie.org.cn ~]#
[root@node101.yinzhengjie.org.cn ~]# bash shell/score.sh
Please input your score: abc
Please input digit
[root@node101.yinzhengjie.org.cn ~]# bash shell/score.sh
Please input your score:
Your score is invalid!
[root@node101.yinzhengjie.org.cn ~]# bash shell/score.sh
Please input your score:
绩效为D,不及格
[root@node101.yinzhengjie.org.cn ~]# bash shell/score.sh
Please input your score:
绩效为C,继续努力
[root@node101.yinzhengjie.org.cn ~]# bash shell/score.sh
Please input your score:
绩效为B,超出任务预期
[root@node101.yinzhengjie.org.cn ~]# bash shell/score.sh
Please input your score:
绩效为A,优秀员工
[root@node101.yinzhengjie.org.cn ~]# bash shell/score.sh
Please input your score:
绩效为S,公司骨干人员
[root@node101.yinzhengjie.org.cn ~]#
[root@node101.yinzhengjie.org.cn ~]#
[root@node101.yinzhengjie.org.cn ~]# vim shell/score.sh #根据分数来判断绩效
二.条件判断case语句
[root@node101.yinzhengjie.org.cn ~]# help case
case: case WORD in [PATTERN [| PATTERN]...) COMMANDS ;;]... esac
Execute commands based on pattern matching. Selectively execute COMMANDS based upon WORD matching PATTERN. The
`|' is used to separate multiple patterns. Exit Status:
Returns the status of the last command executed.
[root@node101.yinzhengjie.org.cn ~]#
[root@node101.yinzhengjie.org.cn ~]# help case #查看case语句的帮助信息
1>.语法格式
case $变量名 in
"值1")
如果变量的值等于1，则执行程序1
；；
"值2")
如果变量的值等于2，则执行程序2
；；
"值3")
如果变量的值等于3，则执行程序3
；；
*）
如果变量的值都不是以上的值，则执行此程序
；；
esac 温馨提示:
case语句和if...elif...else语句一样都是多分支条件语句，不过if多分支语句不同的是，case语句只能判断一种条件关系，而if语句可以判断多种条件关系。
case支持glob风格的通配符：
*: 任意长度任意字符
?: 任意单个字符
[]：指定范围内的任意单个字符
a|b: a或b
2>.案例展示
[root@node101.yinzhengjie.org.cn ~]# vim shell/choose.sh #编写选择的地方并打印
[root@node101.yinzhengjie.org.cn ~]#
[root@node101.yinzhengjie.org.cn ~]# cat shell/choose.sh
#!/bin/bash
#
#********************************************************************
#Author: yinzhengjie
#QQ:
#Date: --
#FileName： shell/choose.sh
#URL: http://www.cnblogs.com/yinzhengjie
#Description： The test script
#Copyright notice: original works, no reprint! Otherwise, legal liability will be investigated.
#******************************************************************** echo "If you want to beijing,please input [1]"
echo "If you want to shanghai,please input [2]"
echo "If you want to shijiazhuang,please input [3]"
echo "If you want to wenzhou,please input [4]" read -t -p "Where do you want to go ? >>> " choose case "$choose" in
"")
echo "Go to beijing!"
;;
"")
echo "Go to shanghai!"
;;
"")
echo "Go to shijiazhuang!"
;;
"")
echo "Go to wenzhou!"
;;
*)
echo "Please enter 1/2/3/4,Thanks!"
;;
esac
[root@node101.yinzhengjie.org.cn ~]#
[root@node101.yinzhengjie.org.cn ~]# bash shell/choose.sh
If you want to beijing,please input []
If you want to shanghai,please input []
If you want to shijiazhuang,please input []
If you want to wenzhou,please input []
Where do you want to go ? >>>
Go to beijing!
[root@node101.yinzhengjie.org.cn ~]# bash shell/choose.sh
If you want to beijing,please input []
If you want to shanghai,please input []
If you want to shijiazhuang,please input []
If you want to wenzhou,please input []
Where do you want to go ? >>>
Go to shanghai!
[root@node101.yinzhengjie.org.cn ~]# bash shell/choose.sh
If you want to beijing,please input []
If you want to shanghai,please input []
If you want to shijiazhuang,please input []
If you want to wenzhou,please input []
Where do you want to go ? >>>
Go to shijiazhuang!
[root@node101.yinzhengjie.org.cn ~]# bash shell/choose.sh
If you want to beijing,please input []
If you want to shanghai,please input []
If you want to shijiazhuang,please input []
If you want to wenzhou,please input []
Where do you want to go ? >>>
Go to wenzhou!
[root@node101.yinzhengjie.org.cn ~]# bash shell/choose.sh
If you want to beijing,please input []
If you want to shanghai,please input []
If you want to shijiazhuang,please input []
If you want to wenzhou,please input []
Where do you want to go ? >>>
Please enter ///,Thanks!
[root@node101.yinzhengjie.org.cn ~]#
[root@node101.yinzhengjie.org.cn ~]#
[root@node101.yinzhengjie.org.cn ~]# vim shell/choose.sh #编写选择的地方并打印
[root@node101.yinzhengjie.org.cn ~]# vim shell/yes_or_no.sh #case版本判断用户输入的是yes还是no
[root@node101.yinzhengjie.org.cn ~]#
[root@node101.yinzhengjie.org.cn ~]# cat shell/yes_or_no.sh
#!/bin/bash
#
#********************************************************************
#Author: yinzhengjie
#QQ:
#Date: --
#FileName： shell/yes_or_no.sh
#URL: http://www.cnblogs.com/yinzhengjie
#Description： The test script
#Copyright notice: original works, no reprint! Otherwise, legal liability will be investigated.
#******************************************************************** read -p "Do you agree?(yes or no)" ANSWER case $ANSWER in
[Yy][Ee][Ss]|[Yy])
echo "YES"
;;
[Nn][Oo]|[Nn])
echo "NO"
;;
*)
echo "NOT YES OR NO"
esac
[root@node101.yinzhengjie.org.cn ~]# bash shell/yes_or_no.sh
Do you agree?(yes or no)y
YES
[root@node101.yinzhengjie.org.cn ~]# bash shell/yes_or_no.sh
Do you agree?(yes or no)yess
NOT YES OR NO
[root@node101.yinzhengjie.org.cn ~]#
[root@node101.yinzhengjie.org.cn ~]# bash shell/yes_or_no.sh
Do you agree?(yes or no)yes
YES
[root@node101.yinzhengjie.org.cn ~]# bash shell/yes_or_no.sh
Do you agree?(yes or no)no
NO
[root@node101.yinzhengjie.org.cn ~]# bash shell/yes_or_no.sh
Do you agree?(yes or no)Y
YES
[root@node101.yinzhengjie.org.cn ~]# bash shell/yes_or_no.sh
Do you agree?(yes or no)Yes
YES
[root@node101.yinzhengjie.org.cn ~]# bash shell/yes_or_no.sh
Do you agree?(yes or no)No
NO
[root@node101.yinzhengjie.org.cn ~]# bash shell/yes_or_no.sh
Do you agree?(yes or no)ye
NOT YES OR NO
[root@node101.yinzhengjie.org.cn ~]#
[root@node101.yinzhengjie.org.cn ~]# vim shell/yes_or_no.sh #case版本判断用户输入的是yes还是no
[root@node101.yinzhengjie.org.cn ~]# vim shell/menu.sh #编写菜单选择案例
[root@node101.yinzhengjie.org.cn ~]#
[root@node101.yinzhengjie.org.cn ~]# cat shell/menu.sh
#!/bin/bash
#
#********************************************************************
#Author: yinzhengjie
#QQ:
#Date: --
#FileName： shell/menu.sh
#URL: http://www.cnblogs.com/yinzhengjie
#Description： The test script
#Copyright notice: original works, no reprint! Otherwise, legal liability will be investigated.
#******************************************************************** cat <<EOF
鲍鱼
海参
佛跳墙
龙虾
帝王蟹
燕窝
EOF read -p "Choose the menu(1-6): " MENU case $MENU in
|)
echo "The price 100"
;;
|)
echo "The price 150"
;;
|)
echo "The price 80"
;;
*)
echo "Choose false"
;;
esac
[root@node101.yinzhengjie.org.cn ~]#
[root@node101.yinzhengjie.org.cn ~]# bash -n shell/menu.sh #对脚本进行语法检查
[root@node101.yinzhengjie.org.cn ~]# bash shell/menu.sh #执行脚本
鲍鱼
海参
佛跳墙
龙虾
帝王蟹
燕窝
Choose the menu(-):
The price
[root@node101.yinzhengjie.org.cn ~]# bash shell/menu.sh
鲍鱼
海参
佛跳墙
龙虾
帝王蟹
燕窝
Choose the menu(-):
The price
[root@node101.yinzhengjie.org.cn ~]# bash shell/menu.sh
鲍鱼
海参
佛跳墙
龙虾
帝王蟹
燕窝
Choose the menu(-):
The price
[root@node101.yinzhengjie.org.cn ~]# bash shell/menu.sh
鲍鱼
海参
佛跳墙
龙虾
帝王蟹
燕窝
Choose the menu(-):
The price
[root@node101.yinzhengjie.org.cn ~]#
[root@node101.yinzhengjie.org.cn ~]# bash shell/menu.sh
鲍鱼
海参
佛跳墙
龙虾
帝王蟹
燕窝
Choose the menu(-):
Choose false
[root@node101.yinzhengjie.org.cn ~]#
[root@node101.yinzhengjie.org.cn ~]# vim shell/menu.sh #编写菜单选择案例
[root@node101.yinzhengjie.org.cn ~]# vim shell/ops_menu.sh #模拟将工作中的任务半自动化，从而提升工作效率。
[root@node101.yinzhengjie.org.cn ~]#
[root@node101.yinzhengjie.org.cn ~]# cat shell/ops_menu.sh
#!/bin/bash
#
#********************************************************************
#Author: yinzhengjie
#QQ:
#Date: --
#FileName： shell/ops_menu.sh
#URL: http://www.cnblogs.com/yinzhengjie
#Description： The test script
#Copyright notice: original works, no reprint! Otherwise, legal liability will be investigated.
#******************************************************************** cat <<EOF
ipaddr
yes_or_no
backup
EOF read -p "Please choose the menu[1-3]: " MENU case $MENU in
)
/root/shell/ip_judge.sh
;;
)
/root/shell/yes_or_no.sh
;;
)
/root/shell/file_backup.sh
;;
*)
echo "你的输入不合法!"
exit
;;
esac
[root@node101.yinzhengjie.org.cn ~]#
[root@node101.yinzhengjie.org.cn ~]# bash shell/ops_menu.sh
ipaddr
yes_or_no
backup
Please choose the menu[-]:
Please input a ip address >>>: 127.0.0.1
127.0.0.1 is legal
[root@node101.yinzhengjie.org.cn ~]# bash shell/ops_menu.sh
ipaddr
yes_or_no
backup
Please choose the menu[-]:
Do you agree?(yes or no)Y
YES
[root@node101.yinzhengjie.org.cn ~]# bash shell/ops_menu.sh
ipaddr
yes_or_no
backup
Please choose the menu[-]:
[root@node101.yinzhengjie.org.cn ~]#
[root@node101.yinzhengjie.org.cn ~]# ll
total
drwxr-xr-x root root Nov : backup
drwxr-xr-x root root Nov : shell
[root@node101.yinzhengjie.org.cn ~]#
[root@node101.yinzhengjie.org.cn ~]# ll backup/
total
-rw-r--r-- root root Nov : boot_2019--.tar.gz
[root@node101.yinzhengjie.org.cn ~]#
[root@node101.yinzhengjie.org.cn ~]# vim shell/ops_menu.sh #模拟将工作中的任务半自动化，从而提升工作效率。
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