Shell 编程简单例子

 

Shell 编程简单例子：

1.     How to write shell script that will add two numbers, which are supplied as command line argument, and if this two numbers are not given show error and its usage?

#!/bin/bash # sum to nos if [ $# -ne 2 ] then     echo "Usage - $0   x    y"     echo "        Where x and y are two nos for which I will print sum"     exit 1 fi echo "Sum of $1 and $2 is `expr $1 + $2`"

2.     Write Script to find out biggest number from given three numbers. Numbers are supplies as command line argument. Print error if sufficient arguments are not supplied?

#!/bin/bash # find out biggest number if [ $# -ne 3 ]     then          echo "$0: number1 number2 number3 are not given" >&2         exit 1        fi     n1=$1     n2=$2     n3=$3     if [ $n1 -gt $n2 ] && [ $n1 -gt $n3 ]     then          echo "$n1 is Bigest number"     elif [ $n2 -gt $n1 ] && [ $n2 -gt $n3 ]             then          echo "$n2 is Bigest number"     elif [ $n3 -gt $n1 ] && [ $n3 -gt $n2 ]             then         echo "$n3 is Bigest number"     elif [ $1 -eq $2 ] && [ $1 -eq $3 ] && [ $2 -eq $3 ]     then          echo "All the three numbers are equal"        else         echo "I can not figure out which number is biger"        fi

 

3.     Write script to print numbers as 5,4,3,2,1 using while loop?

#!/bin/bash # print numbers as 5,4,3,2,1 using while loop i=5 while test $i != 0 do          echo "$i"          i=`expr $i - 1` done

 

4.     Write Script, using case statement to perform basic math operation. The name of script must be 'q4' which works as follows $ ./q4  20 / 3, Also check for sufficient command line arguments?

#!/bin/bash # using case statement to perform basic math operation if test $# = 3 then         case $2 in          +) let z=$1+$3;;          -) let z=$1-$3;;          /) let z=$1/$3;;          x|X) let z=$1*$3;;          *) echo Warning - $2 invalied operator, only +,-,x,/ operator allowed             exit;;         esac         echo Answer is $z else         echo "Usage - $0   value1  operator value2"         echo "        Where, value1 and value2 are numeric values"         echo "               operator can be +,-,/,x (For Multiplication)" fi

 

5.     Write Script to see current date, time, username, and current directory?

#!/bin/bash # see current date, time, username, and current directory echo "Hello, $LOGNAME" echo "Current date is `date`" echo "User is `who i am`" echo "Current direcotry `pwd`"

 

6.     Write script to print given number in reverse order, for eg, if number is 123 it must print as 321?

#!/bin/bash # print given number in reverse order if [ $# -ne 1 ] then     echo "Usage: $0   number"     echo "       I will find reverse of given number"     echo "       For eg. $0 123, I will print 321"     exit 1 fi   n=$1 rev=0 sd=0   while [ $n -gt 0 ] do     sd=`expr $n % 10`     rev=`expr $rev /* 10  + $sd`     n=`expr $n / 10`     echo "$sd $rev $n" done     echo  "Reverse number is $rev"

 

7.     Write script to print given numbers sum of all digit, For eg. If number is 123 it's sum of all digit will be 1+2+3 = 6?

#!/bin/bash # print given numbers sum of all digit if [ $# -ne 1 ] then     echo "Usage: $0   number"     echo "       I will find sum of all digit for given number"     echo "       For eg. $0 123, I will print 6 as sum of all digit (1+2+3)"     exit 1 fi   n=$1 sum=0 sd=0 while [ $n -gt 0 ] do     sd=`expr $n % 10`     sum=`expr $sum + $sd`     n=`expr $n / 10` done     echo  "Sum of digit for number is $sum"

 

8.     How to perform real number calculation in shell script and store result to
third variable , lets say a=5.66, b=8.67, c=a+b?

#!/bin/bash # perform real number calculation a=5.66 b=8.67 c=`echo $a + $b | bc` echo "$a + $b = $c"

 

9.     Write script to determine whether given file exist or not, file name is supplied as command line argument, also check for sufficient number of command line argument?

#!/bin/bash # determine whether given file exist or not if [ $# -ne 1 ] then     echo "Usage - $0  file-name"     exit 1 fi   if [ -f $1 ] then     echo "$1 file exist" else     echo "Sorry, $1 file does not exist" fi

 

10.  Write script to determine whether given command line argument ($1) contains "*" symbol or not, if $1 does not contains "*" symbol add it to $1, otherwise show message "Symbol is not required"?

#!/bin/bash # determine whether given command line argument ($1) contains "*" cat "$1" > /tmp/file.$$   2>/tmp/file0.$$ grep "*"  /tmp/file.$$    >/tmp/file0.$$   if [ $? -eq 1 ] then     echo "Required i.e. $1/*" else     echo "Symbol is Not required"    fi      rm -f /tmp/file.$$ rm -f /tmp/file0.$$

 

11.  Write script to print contains of file from given line number to next given number of lines?

#!/bin/bash # # Print error / diagnostic for user if no arg's given # if [ $# -eq 0 ] then     echo "$0:Error command arguments missing!"     echo "Usage: $0 start_line   uptoline   filename"     echo "Where start_line is line number from which you would like to print file"     echo "uptoline is line number upto which would like to print"     echo "For eg. $0 5 5 myfile"     echo "Here from myfile total 5 lines printed starting from line no. 5 to"     echo "line no 10."     exit 1 fi   # # Look for sufficent arg's #     if [ $# -eq 3 ]; then         if [ -e $3 ]; then             tail +$1 $3 | head -n$2          else             echo "$0: Error opening file $3"             exit 2         fi     else         echo "Missing arguments!"     fi

 

12.  Write script to implement getopts statement, your script should understand following command line argument called this script Q12, Where options work as
-c clear the screen
-d show list of files in current working directory
-m start mc (midnight commander shell) , if installed
-e { editor } start this { editor } if installed?

#!/bin/bash # implement getopts statement # # Function to clear the screen # cls() {     clear     echo "Clear screen, press a key . . ."     read     return }   # # Function to show files in current directory # show_ls() {       ls     echo "list files, press a key . . ."     read     return }   # # Function to start mc # start_mc() {     if which mc > /dev/null ; then          mc          echo "Midnight commander, Press a key . . ."          read     else          echo "Error: Midnight commander not installed, Press a key . . ."          read     fi                 return }   # # Function to start editor # start_ed() {     ced=$1     if which $ced > /dev/null ; then          $ced          echo "$ced, Press a key . . ."          read     else          echo "Error: $ced is not installed or no such editor exist, Press a key . . ."          read     fi                 return }   # # Function to print help # print_help_uu() {             echo "Usage: $0 -c -d -m -v {editor name}";             echo "Where -c clear the screen";             echo "      -d show dir";             echo "      -m start midnight commander shell";             echo "      -e {editor}, start {editor} of your choice";             return }   # # Main procedure start here # # Check for sufficent args #   if [ $# -eq 0 ] ; then     print_help_uu     exit 1 fi      # # Now parse command line arguments # while getopts cdme: opt do     case "$opt" in          c) cls;;          d) show_ls;;          m) start_mc;;          e) thised="$OPTARG"; start_ed $thised ;;          /?) print_help_uu; exit 1;;     esac done

 

13.  Write script called sayHello, put this script into your startup file called .bash_profile, the script should run as soon as you logon to system, and it print any one of the following message in infobox using dialog utility, if installed in your system, If dialog utility is not installed then use echo statement to print message : Good Morning,Good Afternoon,Good Evening , according to system time?

#!/bin/bash # sayHello using dialog utility   temph=`date | cut -c12-13` dat=`date +"%A %d in %B of %Y (%r)"`   if [ $temph -lt 12 ] then     mess="Good Morning $LOGNAME, Have nice day!" fi   if [ $temph -gt 12 -a $temph -le 16 ] then     mess="Good Afternoon $LOGNAME" fi   if [ $temph -gt 16 -a $temph -le 18 ] then     mess="Good Evening $LOGNAME" fi   if which dialog > /dev/null then     dialog --backtitle "Linux Shell Script Tutorial"/     --title "(-: Welcome to Linux :-)"/     --infobox "/n$mess/nThis is $dat" 6 60     echo -n "                            Press a key to continue. . .                        "     read     clear else     echo -e "$mess/nThis is $dat" fi