5 Shell Scripts for Linux Newbies to Learn Shell Programming – Part II

This article is an extension of our First article Understand Linux Shell and Basic Shell Scripting – Part I, where we gave you a taste of Scripting, continuing that we won’t disappoint you in this article.

Script 1: Drawing a Special Pattern

#!/bin/bashMAX_NO=0echo -n "Enter Number between (5 to 9) : "read MAX_NOif ! [ $MAX_NO -ge 5 -a $MAX_NO -le 9 ] ; then   echo "WTF... I ask to enter number between 5 and 9, Try Again"   exit 1ficlearfor (( i=1; i<=MAX_NO; i++ )) do     for (( s=MAX_NO; s>=i; s-- ))    do       echo -n " "    done    for (( j=1; j<=i;  j++ ))     do      echo -n " ."      done     echo "" done ###### Second stage ###################### for (( i=MAX_NO; i>=1; i-- ))do    for (( s=i; s<=MAX_NO; s++ ))    do       echo -n " "    done    for (( j=1; j<=i;  j++ ))    do     echo -n " ."    done    echo ""doneecho -e "\n\n\t\t\t Whenever you need help, Tecmint.com is always there"

Most of the above ‘key words‘ would be known to you and most of them are self explanatory. e.g., MAX sets the maximum value of the variable, for is a loop and anything within the loop gets on executing again and again till the loop is valid for given value of input.

Sample Output

[root@tecmint ~]# chmod 755 Special_Pattern.sh[root@tecmint ~]# ./Special_Pattern.shEnter Number between (5 to 9) : 6       .      . .     . . .    . . . .   . . . . .  . . . . . .  . . . . . .   . . . . .    . . . .     . . .      . .       .                         Whenever you need help, Tecmint.com is always there

If you are a little aware of any programming language, learning the above script is not difficult, even if you are new to computation, programming and Linux it is not going to be much difficult.

Download Special_Pattern.sh

Script 2: Creating Colorful Script

Who says, Linux is colorless and boring, save the codes below to anything [dot] sh, make it executable and Run it, don’t forget to tell me how it was, Think what you can achieve, implementing it somewhere.

#!/bin/bashclear echo -e "33[1m Hello World"# bold effectecho -e "33[5m Blink"# blink effectecho -e "33[0m Hello World"# back to normalecho -e "33[31m Hello World"# Red colorecho -e "33[32m Hello World"# Green colorecho -e "33[33m Hello World"# See remaining on screenecho -e "33[34m Hello World"echo -e "33[35m Hello World"echo -e "33[36m Hello World"echo -e -n "33[0m"# back to normalecho -e "33[41m Hello World"echo -e "33[42m Hello World"echo -e "33[43m Hello World"echo -e "33[44m Hello World"echo -e "33[45m Hello World"echo -e "33[46m Hello World"echo -e "33[0m Hello World"

Note: Don't bother about the color code now, Those important to you will be at your tongue, gradually.

Warning: Your terminal might not have the facility of blinking.

Sample Output

[root@tecmint ~]# chmod 755 Colorfull.sh[root@tecmint ~]# ./Colorfull.shHello WorldBlinkHello WorldHello WorldHello WorldHello WorldHello WorldHello WorldHello WorldHello WorldHello WorldHello WorldHello WorldHello WorldHello WorldHello World

Download Colorfull.sh

Script 3: Encrypt a File/Directory

This script will encrypt a file (remember? directory/driver/…. everything is treated as file, in Linux). The current limitation of the above script is that it don’t support auto completion of name using TAB. Moreover, you need to place the script and file to be encrypted in the same folder. You may need to install “pinentry-gui”, using yum or apt the package, if required.

[root@midstage ~]# yum install pinentry-gui[root@midstage ~]# apt-get install pinentry-gui

Crete a file called “Encrypt.sh” and place the following script, make it executable and run it as shown.

#!/bin/bashecho "Welcome, I am ready to encrypt a file/folder for you"echo "currently I have a limitation, Place me to thh same folder, where a file to be encrypted is present"echo "Enter the Exact File Name with extension"read file;gpg -c $fileecho "I have encrypted the file successfully..."echo "Now I will be removing the original file"rm -rf $file

Sample Output

[root@tecmint ~]# chmod 755 Encrypt.sh[root@tecmint ~]# ./Encrypt.shWelcome, I am ready to encrypt a file/folder for youcurrently I have a limitation, Place me to the same folder, where a file to beencrypted is presentEnter the Exact File Name with extensionpackage.xml                                                   ┌─────────────────────────────────────────────────────┐                                                   │ Enter passphrase                                    │                                                   │                                                     │                                                   │                                                     │                                                   │ Passphrase *******_________________________________ │                                                   │                                                     │                                                   │       <OK>                             <Cancel>     │                                                   └─────────────────────────────────────────────────────┘Please re-enter this passphrase                                                   ┌─────────────────────────────────────────────────────┐                                                   │ Please re-enter this passphrase                     │                                                   │                                                     │                                                   │ Passphrase ********________________________________ │                                                   │                                                     │                                                   │       <OK>                             <Cancel>     │                                                   └─────────────────────────────────────────────────────┘I have encrypted the file successfully...Now I will be removing the original file</pre>

gpg -c : This will encrypt your file, using a passkey aka password. In this process of learning you would have never thought that the actual process of learning could be that much easy. So after encrypting a file what you need? Obviously! decrypting the file. And I want you – the learner, the reader to write the decryption script yourself, don’t worry I am not leaving you in the middle, I just want you to gain something out of this article.

Note: gpg -d filename.gpg > filename is what you need to implement in your decryption script. You may post you script in comment if successful, if not you may ask me to write it for you.

Download Encrypt.sh

Script 4: Checking Server Utilization

Checking the server utilization is one of the important task of an administrator, and a good administrator is one who knows how to automate his day to day task. Below is the script that will give many such information about your server. Check it yourself.

#!/bin/bash    date;    echo "uptime:"    uptime    echo "Currently connected:"    w    echo "--------------------"    echo "Last logins:"    last -a |head -3    echo "--------------------"    echo "Disk and memory usage:"    df -h | xargs | awk '{print "Free/total disk: " $11 " / " $9}'    free -m | xargs | awk '{print "Free/total memory: " $17 " / " $8 " MB"}'    echo "--------------------"    start_log=`head -1 /var/log/messages |cut -c 1-12`    oom=`grep -ci kill /var/log/messages`    echo -n "OOM errors since $start_log :" $oom    echo ""    echo "--------------------"    echo "Utilization and most expensive processes:"    top -b |head -3    echotop -b |head -10 |tail -4    echo "--------------------"    echo "Open TCP ports:"    nmap -p- -T4 127.0.0.1    echo "--------------------"    echo "Current connections:"    ss -s    echo "--------------------"    echo "processes:"    ps auxf --width=200    echo "--------------------"    echo "vmstat:"    vmstat 1 5

Sample Output

[root@tecmint ~]# chmod 755 Server-Health.sh[root@tecmint ~]# ./Server-Health.shTue Jul 16 22:01:06 IST 2013uptime: 22:01:06 up 174 days,  4:42,  1 user,  load average: 0.36, 0.25, 0.18Currently connected: 22:01:06 up 174 days,  4:42,  1 user,  load average: 0.36, 0.25, 0.18USER     TTY      FROM              LOGIN@   IDLE   JCPU   PCPU WHATtecmint   pts/0    116.72.134.162   21:48    0.00s  0.03s  0.03s sshd: tecmint [priv]--------------------Last logins:tecmint   pts/0        Tue Jul 16 21:48   still logged in    116.72.134.162tecmint   pts/0        Tue Jul 16 21:24 - 21:43  (00:19)     116.72.134.162--------------------Disk and memory usage:Free/total disk: 292G / 457GFree/total memory: 3510 / 3838 MB--------------------OOM errors since Jul 14 03:37 : 0--------------------Utilization and most expensive processes:top - 22:01:07 up 174 days,  4:42,  1 user,  load average: 0.36, 0.25, 0.18Tasks: 149 total,   1 running, 148 sleeping,   0 stopped,   0 zombieCpu(s):  0.1%us,  0.0%sy,  0.0%ni, 99.3%id,  0.6%wa,  0.0%hi,  0.0%si,  0.0%st  PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND    1 root      20   0  3788 1128  932 S  0.0  0.0   0:32.94 init    2 root      20   0     0    0    0 S  0.0  0.0   0:00.00 kthreadd    3 root      RT   0     0    0    0 S  0.0  0.0   0:14.07 migration/0

Note: I have given you the script that gives the output in the terminal itself, how about getting the output in a file for future reference. Implement it using redirect operator.

1. ‘>‘ : the redirection operator causes a file creation, and if it does exist, the contents are overwritten.
2. ‘>>‘ : when you use >>, you are adding information, rather than replacing it.
3. ‘>>‘ is safe, as compared to ‘>‘

Download Server-Health.sh

Script 5: Check Disk Space and Sends an Email Alert

How about getting an email when disk use in partition PART is bigger than Maximum allowed, it is a life saver script for web administrators with little modification.

MAX=95EMAIL=[e-mail]=sda1USE=`df -h |grep $PART | awk '{ print $5 }' | cut -d'%' -f1`if [ $USE -gt $MAX ]; then  echo "Percent used: $USE" | mail -s "Running out of disk space" $EMAILfi

Note: Remove “USER” with your user name. You can check mail using using ‘mail‘ command.

Download Check-Disk-Space.sh

Script writing and programming is beyond boundaries, anything and everything could be implemented as required. That’s all for now, In my very next article I will be giving your some different flavors of scripting. Till then stay cool and tuned, enjoy.