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

To Learn something you need to do it, without the fear of being unsuccessful. I believe in practicality and hence will be accompanying you to the practical world of Scripting Language.

Learn Basic Shell Scripting

Learn Basic Shell Scripting

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/bash
MAX_NO=0
echo -n "Enter Number between (5 to 9) : "
read MAX_NO
if ! [ $MAX_NO -ge 5 -a $MAX_NO -le 9 ] ; then
   echo "WTF... I ask to enter number between 5 and 9, Try Again"
   exit 1
fi
clear
for (( 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 ""
done
echo -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
[[email protected] ~]# chmod 755 Special_Pattern.sh
[[email protected] ~]# ./Special_Pattern.sh
Enter 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/bash
clear 
echo -e "33[1m Hello World"
# bold effect
echo -e "33[5m Blink"
# blink effect
echo -e "33[0m Hello World"
# back to normal
echo -e "33[31m Hello World"
# Red color
echo -e "33[32m Hello World"
# Green color
echo -e "33[33m Hello World"
# See remaining on screen
echo -e "33[34m Hello World"
echo -e "33[35m Hello World"
echo -e "33[36m Hello World"
echo -e -n "33[0m"
# back to normal
echo -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
[[email protected] ~]# chmod 755 Colorfull.sh
[[email protected] ~]# ./Colorfull.sh

Hello World
Blink
Hello World
Hello World
Hello World
Hello World
Hello World
Hello World
Hello World
Hello World
Hello World
Hello World
Hello World
Hello World
Hello World
Hello 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.

[[email protected] ~]# yum install pinentry-gui
[[email protected] ~]# 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/bash
echo "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 $file
echo "I have encrypted the file successfully..."
echo "Now I will be removing the original file"
rm -rf $file

Sample Output

[[email protected] ~]# chmod 755 Encrypt.sh
[[email protected] ~]# ./Encrypt.sh

Welcome, I am ready to encrypt a file/folder for you
currently I have a limitation, Place me to the same folder, where a file to be

encrypted is present
Enter the Exact File Name with extension

package.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
    echo
	top -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
[[email protected] ~]# chmod 755 Server-Health.sh
[[email protected] ~]# ./Server-Health.sh

Tue Jul 16 22:01:06 IST 2013
uptime:
 22:01:06 up 174 days,  4:42,  1 user,  load average: 0.36, 0.25, 0.18
Currently connected:
 22:01:06 up 174 days,  4:42,  1 user,  load average: 0.36, 0.25, 0.18
USER     TTY      FROM              [email protected]   IDLE   JCPU   PCPU WHAT
tecmint   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    116.72.134.162
tecmint   pts/0        Tue Jul 16 21:24 - 21:43  (00:19)     116.72.134.162
--------------------
Disk and memory usage:
Free/total disk: 292G / 457G
Free/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, 0.18
Tasks: 149 total,   1 running, 148 sleeping,   0 stopped,   0 zombie
Cpu(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=95
[email protected]
PART=sda1
USE=`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" $EMAIL
fi

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.

Best Affordable Linux and WordPress Services For Your Business
Outsource Your Linux and WordPress Project and Get it Promptly Completed Remotely and Delivered Online.

If You Appreciate What We Do Here On TecMint, You Should Consider:

  1. Stay Connected to: Twitter | Facebook | Google Plus
  2. Subscribe to our email updates: Sign Up Now
  3. Get your own self-hosted blog with a Free Domain at ($3.45/month).
  4. Become a Supporter - Make a contribution via PayPal
  5. Support us by purchasing our premium books in PDF format.
  6. Support us by taking our online Linux courses

We are thankful for your never ending support.

RedHat RHCE and RHCSA Certification Book
Linux Foundation LFCS and LFCE Certification Preparation Guide

You may also like...

90 Responses

  1. Hritik Maurya says:

    Please give the decryption code i had tried writing but not working..

  2. mithran says:

    Hi, what does cut -d % -f1 represent?

  3. Just_A_Newbie says:

    Hi! Thanks for this article. It is very useful. However, I have found that for Centos6 or Centos7, you have to add "\" into the command for the Colourful Script to activate the -e command.

  4. Amit Alone says:

    ### Below is the decryption script####

    #!/bin/bash
    echo "Welcome, I am ready to decrypt a file/folder for you"
    echo "currently I have a limitation, Place me to the same folder, 
    where a file to be decrypt is present"
    echo "Enter the Exact File Name with extension"
    read file;
    gpg -d $file > decpt.txt
    echo "I have decrypt the file successfully..."
    echo "Please confirm should we remove the original file. Please answer in Y or N"
    read answer
    if [ "$answer" == Y ];
    then
     rm -rf $file
     echo " We have removed the file successfully..."
    else
     echo "Thank You."
    fi
    
  5. qazi abid says:

    Hello,

    Actually I tried file encrypt script but when I execute the code it gives me error. Can you please send me how to do it will really appreciate your help.

    Thank you

  6. Petterock says:

    Hi.
    You can try this.

    #!/bin/bash
    #Creador Alfredo Pettengill – Rollout-IT

    df=”$(df -hP | egrep ‘^/dev/’ | awk ‘{ print $6 “_:_” $5 }’ )”
    hostname=”$HOSTNAME”
    CPU=”$(top -bn1 | grep load)”
    free=”$(free -mt | grep Mem: )”
    THRESHOLD=75
    user=”$(who)”
    if [[ “$df” > “$THRESHOLD” ]]
    then

    mail -s ‘Disk Alert ‘$hostname’ ‘ [email protected] << EOF
    Server Disk Space $hostname. Usado:

    $df

    —Server RAM Memory—

    Total Used Free Shared Buffer Cache
    $free

    —Server CPU usage—

    $CPU

    —Loggin Users—

    $user
    EOF
    fi

  7. Francesco says:

    Hi, good article. Perhaps when you are searching for OOM messages it is better to search the string “Out of memory” as with “kill” you would find more output then required.
    Thanks

  8. Dede says:

    Hello,
    A friend show me a website named UsiScript (http://www.usiscript.com). It’s a tool that help you to create a bash script, even you don’t know the syntax. It’s simple and fast.

  9. mandeep says:

    You all guys are the best….
    One request to all of you pls explain every field in script for more understanding to the readers.
    Thank you all.

Got something to say? Join the discussion.

Your email address will not be published. Required fields are marked *

This site uses Akismet to reduce spam. Learn how your comment data is processed.