shell学习之条件测试（参考shell脚本编程诀窍）
1关于test测试，查看man文档知
表达式的判断
( EXPRESSION ) #EXPRESSION is true
! EXPRESSION #EXPRESSION is false
EXPRESSION1 -a EXPRESSION2 #both are true,-o means or
字符串是否为空，相等
-n STRING #the length of STRING is nonzero,-n can be removed
-z STRING #the length of STRING is zero（nonexists,or null)
#when comes to string, we use =
STRING1 = STRING2 #the strings are equal
STRING1 != STRING2 #the strings are not equal
数字的比较
#when comes to number,we use different eq ne and so on
INTEGER1 -eq INTEGER2 #INTEGER1 is equal to INTEGER2
-ge greater or equal
-gt greater than
-le -lt -ne I
比较文件是否为链接文件
FILE1 -ef FILE2 #FILE1 and FILE2 have the same device and inode numbers
eg
[root@www shell]# test txt -ef txthardlink [root@www shell]# echo $? 0 [root@www shell]# test txt -ef txtlink(soft) [root@www shell]# echo $? 0
所以这个是测试是否是文件链接（包括软硬），大家可以自己试试
比较文件的修改时间
FILE1 -nt FILE2 #FILE1 is newer/older (modification date) than FILE2，timestamp
FILE1 -ot FILE2 文件有修改时间modify time （强调内容改变） 改变时间change time（本质即相关属性改变） 接触时间access time（被访问）
文件类型
-b FILE #type:block special
-c FILE #type:character special
-d FILE # a directory
-e FILE #FILE exists是否存在
-s FILE #FILE exists and has a size greater than zero是否为空
-f FILE #a regular file
-u FILE #set user-ID SUID
-g FILE #FILE exists and is set-group-ID使用时暂时拥有文件所属组的权限SGID
-G FILE #FILE exists and is owned by the effective group ID真的Group
-h FILE #a symbolic link (same as -L)
-k FILE #FILE exists and has its sticky bit set sticky位其他用户只能添加不能删除
-L FILE #FILE exists and is a symbolic link (same as -h)
-O FILE #FILE exists and is owned by the effective user ID
-p FILE #a named pipe
-S FILE #FILE exists and is a socket
-r FILE #FILE exists and read permission is granted
you can use -w ,write ,-x execute
-t FD #file descriptor FD is opened on a terminal
很多，但有规律，常用的并不多
2 上面的测试还可用于类似[ -e $num ]结构中
3 if/then条件测试结构（还有case，while，等结构可能后面会涉及，不懂请自行baidu）
①if [ condition ]
then
COMMAND
fi
or
if [ condition ];then
COMMAND
fi
②if [ condition ];then
COMMAND1
else
COMMAND2
fi
③if [ condition ];then
COMMAND1
elif [ condition ];then
COMMAND2
else
COMMAND3
fi
big eg.
#if1.sh #!/bin/bash # read -p "guss who am i?" HELLO test -z $HELLO&&echo "wrong argv please reinput!"&&exit 1 if [ "$HELLO" = "Jack" ];then echo "oh,you are jack!" elif [ "$HELLO" = "Kitty" ];then echo "oh,you are Kitty!" elif [ "$HELLO" = "Mike" ];then echo "oh,you are Mike!" else echo "sorry i don't remember." echo "ok,my name is $HELLO" fi
通常if then可以改为[[ conditon ]]&&条件ok||条件不ok
3 [[ ]]与[]的区别
通常表现在以下几个方面
[ ]使用-a，-o连接多个逻辑表达式，而[[ ]]使用&&，||连接多个表达式
[ ]：通配符不起作用，[[ ]]会展开通配符
[ ]不能使用比较运算符，如>，<，而[[ ]]可以4 (())
测试数字表达式
结果为0返回1，结果为其他返回0
[root@www ~]# ((1-1))
[root@www ~]# echo $?
1
[root@www ~]# ((1+1))
[root@www ~]# echo $?
0
5 条件判断与测试的小程序
#-N可以表示文件是否被修改
#所以有下面的一段监控文件是否被修改的shell script
#watchfile.sh
#!/bin/bash
TT=5 #5 seconds
NFILE=$1 #the watched file
#origin length of the file
len=`wc -l $NFILE |awk '{print $1 }'`
echo " $NFILE has $len lines "
while :
do
if [ -N $NFILE ]
then
echo "`date`:new entry in $NFILE"
newlen=`wc -l $NFILE |awk '{print $1 }'`
newlines=`expr $newlen - $len`
tail -$newlines $NFILE
len=$newlen
fi
sleep $TT
done
6 正则表达式的测试程序
#RE.sh #!/bin/bash for deb in /root/shell/* do pkgname=`basename $deb` if [[ $pkgname =~ .*\.deb ]];then #提醒 if紧跟着的[有空格，$前面有一个空格，deb后面有个空格 echo "FILE $pkgname is a debian package" else echo "File $pkgname is not a debian package" fi done
另一个添加捕获的
#如何捕获括号中的字符串
#保存在BASH_REMATCH[]数组中
#RE1.sh
#!/bin/bash
# manage to know your name
read -p "please input your fullname：" NAME
if [[ $NAME =~ (.*)[[:space:]](.*) ]];then
echo "你姓 ${BASH_REMATCH[2]}"
echo "你叫 ${BASH_REMATCH[1]}"
echo "全称 ${BASH_REMATCH[0]}"
fi
执行结果
[root@www shell]# ./RE1.sh
please input your fullname:liancao liu
你姓 liu
你叫 liancao
全称 liancao liu
7 一个猜数字的脚本
#一个猜数字的sh #numguess.sh #!/bin/bash #you may want to guess between 0-50 WORDS=51 GUESS=-1 TIME=0 BELOW=0 TOP=`expr $WORDS - 1 ` let ANSWER=($RANDOM % $WORDS) let ANSWER+=-1 while [ "$GUESS" -ne "$ANSWER" ] do echo "the number is between $BELOW and $TOP" read -p "your guess:" GUESS let TIME+=1 if [ "$GUESS" -lt "$ANSWER" ] ;then echo "please input larger" BELOW=`expr $GUESS + 1` elif [ "$GUESS" -gt "$ANSWER" ];then echo "please input smaller" TOP=`expr $GUESS - 1 ` else echo "right! you guessed $TIME times" fi done