Shell流程控制(if,else,case【88bf必发娱乐】,while,for,until)

1.条件选择


1.1.if
语句

  语法十分简单

#!/bin/bash

MATH_SCORES="$1"
NAME="$2"

if [ -z "${MATH_SCORES}" ]
then
  printf "The command requires that options have a scores.\n"
  printf "What's ths scores of your math? :"
  read MATH_SCORES
fi

if [ -z "${NAME}" ]
then
  printf "The command requires that options have a student's name.\n"
  printf "What's your name? :"
  read NAME
fi

if [ "${NAME}" = "sunny" ]
then
  printf "No, sunny is a teacher.\nPleae input your name,ok? "
  read NAME
  printf "My god,i think, you are bann sunny, excuse me.\n\n"
else
  printf "\n"
fi

if [ "${MATH_SCORES}" -ge 90 ]
then
  echo "Your scores is very good.Congratulations to you, ${NAME}."
  echo "I hope that you are't sunny."
else if [ "${MATH_SCORES}" -ge 60 ]
then
  echo "Congratulations. ${NAME}"
elif [ "${MATH_SCORES}" -ge 50 ]
then
  echo "Come on ${NAME}."
else
  echo "What are you interested in? Please tell me, maybe i can help you, "${NAME}" ?"
fi;fi

echo
[web@h p]$ ./if_then_else.sh 37
The command requires that options have a student's name.
What's your name? :sunny
No, sunny is a teacher.
Pleae input your name,ok? sunny
My god,i think, you are bann sunny, excuse me.

What are you interested in? Please tell me, maybe i can help you, sunny ?

  语句体,以fi结束。

 

  利用选择语句判断变量获取成功与否

JAVA_PATH=`which java 2>/dev/null`
if [ "x$JAVA_PATH" != "x" ]; then
    JAVA_PATH=`dirname $JAVA_PATH 2>/dev/null`
    JRE_HOME=`dirname $JAVA_PATH 2>/dev/null`
fi

 

1.2.case
语句

  双分号不能少;跟if一样,语句体也需要结束符。

  找工作时,根据应聘岗位不同,给出不同应征者相应的联系人信息。

#!/bin/bash

echo -e "\v\tRecruitment Announcement"
echo "Are you ready to apply for any job?"
echo "1 accounting"
echo "2 cashier"
echo "3 secretary"
echo -e "\vPlease enter a number to select the corresponding positions."

read NUM
case $NUM in
  1)
    printf "call mr wang. number is 1124\n"
    ;;
  2)
    printf "call miss li. number is 1233.\n"
    ;;
  3)
    printf "call miss ji. number is 1367.\n"
    ;;
  *)
    printf "If you want to make a lot of money, to be a seller. call 1498.\n"
    ;;
esac

 

  在输出交互信息时,使用了echo命令。当要格式化输出时,需要来回调试。这里仅仅为了熟悉下case语句的语法,更好的方法在“cat”博文里重新实现。

   使用case语句,处理坐标移动的结果。

#!/bin/bash

echo $(date)
X1=0
Y1=0

echo "L - turn left"
echo "R - turn right"
echo "U - turn up"
echo "D - turn down"
read INS

case $INS in
  L)
    X1=$[${X1}-1]
    ;;
  R)
    X1=$[${X1}+1]
    ;;
  U)
    Y1=$[${Y1}+1]
    ;;
  D)
    Y1=$[${Y1}-1]
    ;;
  [[:lower:]])
    printf "Uppers, please.\n"
    ;;
  *)
    ;;
esac

echo "x = ${X1} y = ${Y1}"

 

  输出脚本的帮助信息:

case "$1" in
    "")
        run_it
        ;;
    -r|--read)
        read_it
        ;;
    -v|--version)
        display_version
        ;;
    --clear)
        clear_TMPFILE
        ;;
    -h|--help)
        display_help
        ;;
    *)
        echo "findTom -h"
        display_help
        ;;
esac

如果“”-v|–version””,以双引号表示,会出现意外。要是想用,就该这么写:“”-v”|”–version””。

 

1.3.通过辑判断实现条件测试

[view@file donatello]$ [ 3 -gt 5 ] && echo "true " || echo "false "
false
[view@file donatello]$ [ ! 3 -gt 5 ] && echo "true " || echo "false "
true


[work@file donatello]$  [ ! 3 -gt 5 ] && ( echo -n "true, "; echo "exit 0" ) || ( echo -n "false, "; echo "exit 1" )
true, exit 0
[work@file donatello]$  [ 3 -gt 5 ] && ( echo -n "true, "; echo "exit 0" ) || ( echo -n "false, "; echo "exit 1" )
false, exit 1

 

2.循环


 

2.1.for循环

  语法格式:

for name[ [in [words…] ] ; ] do commands; done
for ((expr1;expr2;expr3)) ; do commands; done

 

[web@h p]$ ls >> java.dir
[web@h p]$ cat java.sh
#!/bin/bash

for i in $(cat java.dir)
do
  echo $i
done

 

计算1加到10

#!/bin/bash

declare -i sum=0
for i in {1..10}
do
        sum=$((sum+i))
done

echo sum = $sum

#!/bin/bash

sum=0
for i in $(seq 1 10)
do
        sum=$((sum+i))
done

echo sum = $sum

 

for
语句不带列表,就从命令行获取列表信息

[web@h p]$ cat t1.sh
#!/bin/bash

for i
do
  echo $i
done
[web@h p]$ sh t1.sh ls
ls
[web@h p]$ sh t1.sh `ls`

 

类C风格(体现在“for”语句中、以及循环体中;变量不需要“$”符号)

#!/bin/bash

SUM=0
MAX=100
MIN=0

for ((i=MIN; i<= MAX; i++))
do
  SUM=$[SUM+i]
done

echo "From ${MIN} add to ${MAX} is $SUM."

 

**2.2.循环until、while**

  条件判断时如果涉及了命令的返回值,该值不管返回了0还是1之类,都需要跟数字比较来控制程序的运行。

#语法

until test-commands; do consequent-commands; done
while test-commands; do consequent-commands; done

 

  while循环是条件满足时开始执行;until循环是条件不满足时开始循环。

  举个例子,条件为假时,才能执行循环体语句:

#!/bin/bash
until false
do
        echo -n '-'
        sleep 1
        echo -e -n '\b\'
        sleep 1
        echo -e -n '\b-'
        sleep 1
        echo -e -n '\b/'
        sleep 1
        echo -e -n '\b*'
done

 

  若是换作了条件满足时执行循环体语句的情况,就可以选择while语句。

  while还可以直接读取文件,在done语句处“done
< /path/to/file”。查看系统默认挂载的特殊文件系统:

#!/bin/bash
#

while read LINE; do
        echo $LINE | grep -v dev &> /dev/null
        if [ $? -eq 0 ]; then
                echo $LINE | awk '{print $1}' | grep -v boot
        fi
done < /etc/fstab

 


bash脚本调试

  检查脚本语法、调试执行脚本

$ bash -n adduser.sh
$ bash -x adduser.sh

 

  shell脚本追踪

  在测试脚本时,可以使用set命令进行运行时的追踪。在脚本中加入一行“set
-x”;以“+”开头的行,就是获得的追踪内容(程序的执行过程)。

[root@right mag]# cat tes.sh 
#!/bin/bash

set -x
read -p "How old are you? " answer
if [ $answer == "34" ]; then
    echo "Yes, very good."
else
    echo "No, i don't want say anyting."
fi

exit 0
[root@right mag]# ./tes.sh 
+ read -p 'How old are you? ' answer
How old are you? 34
+ '[' 34 == 34 ']'
+ echo 'Yes, very good.'
Yes, very good.
+ exit 0
[root@right mag]# ./tes.sh 
+ read -p 'How old are you? ' answer
How old are you? 33
+ '[' 33 == 34 ']'
+ echo 'No, i don'\''t want say anyting.'
No, i don't want say anyting.
+ exit 0

 

  看看没有追踪的执行过程:

[root@right mag]# ./tes.sh 
How old are you? 32
No, i don't want say anyting.