$1 represents parameter 1
$2 represents parameter 2
likewise
For Example:
startup.sh
#!/bin/bash
echo hello $1 $2
on command line :./startup.sh dinesh donthaoutput:hello dinesh donthaFriday, 12 February 2021
How to do I send parameters to bash script / shell script?
You can send parameters from command-line to a bash script using $1 $2 ...
Thursday, 11 February 2021
Most used Linux commands when working on servers / when ssh to remote systems
tail -100f catalina.out
let's say we want to run the latest current running logs with last 100 lines, then you should use the above command.
cd <specific folder>
useful to change to mentioned directory
cd ..
useful to change back to parent directory, one level down
mkdir <dir_name>
creates a new directory with given name <dir_name>
mkdir -p <dir1/dir2/dir3>
creates the directory structure, which fails to do without -p option
rm -r <dir1/dir2/dir3>
removes the complete directory structure, regardless of number of internal directories, which fails to remove without -r option.
How to install correct combination of nodejs and npm on mac / windows ?
I would recommend different installation process on mac rather than installing the nodejs using brew command line.
- Just go to https://nodejs.org/en/download/releases/
- For example, if you want nodejs v6.9.4 and its compatible npm v3.10.10 on MAC, then download the node-v6.9.4.pkg file of specified version, which automatically installs its compatible npm version 3.10.10.
- Likewise, you don't need npm to install nodejs, but you can directly install required nodejs version which brings its compatible npm version automatically.
Note: If you are working on Mac / Windows, then you find the respective installers for installation. If you are working on Linux based OS, you would need to download .tar files.
Index of /download/release/v6.9.4/
../ docs/ 05-Jan-2017 21:30 - win-x64/ 05-Jan-2017 21:04 - win-x86/ 05-Jan-2017 21:23 - SHASUMS256.txt 05-Jan-2017 23:33 3865 SHASUMS256.txt.asc 05-Jan-2017 23:33 4369 SHASUMS256.txt.sig 05-Jan-2017 23:33 287 node-v6.9.4-aix-ppc64.tar.gz 05-Jan-2017 21:08 17397618 node-v6.9.4-darwin-x64.tar.gz 05-Jan-2017 21:29 12041778 node-v6.9.4-darwin-x64.tar.xz 05-Jan-2017 21:30 8316788 node-v6.9.4-headers.tar.gz 05-Jan-2017 21:35 476961 node-v6.9.4-headers.tar.xz 05-Jan-2017 21:35 346992 node-v6.9.4-linux-arm64.tar.gz 05-Jan-2017 20:52 13216193 node-v6.9.4-linux-arm64.tar.xz 05-Jan-2017 20:52 8413528 node-v6.9.4-linux-armv6l.tar.gz 05-Jan-2017 21:27 13058040 node-v6.9.4-linux-armv6l.tar.xz 05-Jan-2017 21:33 8291812 node-v6.9.4-linux-armv7l.tar.gz 05-Jan-2017 21:03 13040155 node-v6.9.4-linux-armv7l.tar.xz 05-Jan-2017 21:05 8304476 node-v6.9.4-linux-ppc64.tar.gz 05-Jan-2017 20:49 13994448 node-v6.9.4-linux-ppc64.tar.xz 05-Jan-2017 20:50 8522364 node-v6.9.4-linux-ppc64le.tar.gz 05-Jan-2017 20:48 13749594 node-v6.9.4-linux-ppc64le.tar.xz 05-Jan-2017 20:48 8655784 node-v6.9.4-linux-s390x.tar.gz 05-Jan-2017 20:46 14201628 node-v6.9.4-linux-s390x.tar.xz 05-Jan-2017 20:46 8933844 node-v6.9.4-linux-x64.tar.gz 05-Jan-2017 20:50 13928019 node-v6.9.4-linux-x64.tar.xz 05-Jan-2017 20:51 9348020 node-v6.9.4-linux-x86.tar.gz 05-Jan-2017 20:52 13411488 node-v6.9.4-linux-x86.tar.xz 05-Jan-2017 20:53 8935060 node-v6.9.4-sunos-x64.tar.gz 05-Jan-2017 21:10 14679106 node-v6.9.4-sunos-x64.tar.xz 05-Jan-2017 21:11 9442348 node-v6.9.4-sunos-x86.tar.gz 05-Jan-2017 23:31 13617149 node-v6.9.4-sunos-x86.tar.xz 05-Jan-2017 23:31 8765124 node-v6.9.4-win-x64.7z 05-Jan-2017 21:05 6868142 node-v6.9.4-win-x64.zip 05-Jan-2017 21:05 12239442 node-v6.9.4-win-x86.7z 05-Jan-2017 21:24 5982803 node-v6.9.4-win-x86.zip 05-Jan-2017 21:24 11026266 node-v6.9.4-x64.msi 05-Jan-2017 21:06 12791808 node-v6.9.4-x86.msi 05-Jan-2017 21:24 11489280 node-v6.9.4.pkg 05-Jan-2017 21:24 15526075 node-v6.9.4.tar.gz 05-Jan-2017 21:31 26379683 node-v6.9.4.tar.xz 05-Jan-2017 21:32 15519264
Monday, 8 February 2021
How to create a Kafka Topic using command line utility ?
Just a quick introduction, we can create Kafka Topic. using command line utility and also using programming APIs.
This post shows command line utility which help us in creating the Kafka Topic.
For your information, under /bin folder of Kafka installation, there are many Kafka Utilities available for various uses, one of which to kafka-topics.sh helps to create topics, describe topics & other topic related stuff.
Before executing the topic command as below, ensure your Zookeeper Server and Kafka Cluster (same order - start Zookeeper 1st then Kafka Cluster service next) has already been started.
Lets say Kafka cluster is having one node with its Kafka Service node running at a default port 9092 & we are trying to create a topic named error-events
$ bin/kafka-topics.sh --create --topic error-events --bootstrap-server localhost:9092Console Output:
Topic created.
To ensure the topic creation, we can describe the topic:
$ bin/kafka-topics.sh --describe --topic error-events --bootstrap-server localhost:9092
Topic:error-events PartitionCount:1 ReplicationFactor:1 Configs:
Topic: error-events Partition: 0 Leader: 0 Replicas: 0 Isr: 0
It prints all the information related to given kafka topic - like partition count, replicator factor, replicas, in-sync replicas (Isr), Leader ...
Saturday, 6 February 2021
What is SPLUNK?
Splunk is a product/tool which captures the real-time data & indexes the data, extracts interesting fields to analyse. We can create various Splunk objects like Alerts, Reports, Dashboards using this real-time data. By doing so, we can analyse various issues happening in Applications that feeds data to the Splunk.
For Example,
- you can find all the 500 errors of your application happened during last 12 Hrs.
- you can find all the intruders or users who are trying to hack the system. For example, if from a particular IP address, if we see some unusual 403 forbidden errors, let say, when the user is trying to enter the password with a lot of trials.
- you can create an alert with the above mentioned scenarios, for example, if we find 500 errors more than 10 in last 4 hrs, we should get an alert.
- We can create Dashboards with all the charts & reports in one place for a better monitoring and analysis.
Splunk provides a search query language of its own, which does have a lot of commands for searching & reporting, often called as "Transforming commands" & "Non-transforming commands". Using these commands - we can analyse & capture the realtime statistics of the application in one place.
Friday, 5 February 2021
How to force the maven to redownload all the packages ?
First Way:
You can use mvn option -U : which forces the maven to download the dependency into local repository (.m2 folder)
Eg:
mvn clean package -U
Second Way:
Use purge-local-repository
Eg:
mvn dependency:purge-local-repository clean package
Third Way:
You can manually directly delete the .m2 folder in computers home directory (like in linux - mac, ~)
@SerializedName annoation: GSON: How to use a different name for serialised fields
you can use GSON annotation @SerializedName annotation for using a different names for serialized fields.
Maven Dependency Needed:
<dependency>
<groupId>com.google.code.gson</groupId>
<artifactId>gson</artifactId>
<version>2.8.6</version>
</dependency> For Example:
import com.google.gson.Gson;
import com.google.gson.GsonBuilder;
import com.google.gson.annotations.SerializedName;
public class GsonExposeAnnotationTest {
public static void main(String[] args) {
Student student = new Student("Dinesh", "ROLL123", "Hyderabad - 500081");
Gson gson = new GsonBuilder().setPrettyPrinting().create();
System.out.println(gson.toJson(student));
}
}
class Student {
@SerializedName("student-name")
String name;
@SerializedName("student-rollno")
String rollNo;
@SerializedName("student-address")
String address;
public Student(String name, String rollNo, String address) {
this.name = name;
this.rollNo = rollNo;
this.address = address;
}
} Output: Serialised output - fields name are different than in POJO { "student-name": "Dinesh", "student-rollno": "ROLL123", "student-address": "Hyderabad - 500081" }
@Expose annotation : GSON : How to exclude / include the fields in serialisation & deserialisation ?
You can use @Expose annotation to exclude or include the fields using GSON library. By default, @Expose serialize & deserialize attributes have true. So you can mention @Expose directly, which intends @Expose(serialize = true, deserialize = true)
Maven Dependency Need: Add this dependency in your pom.xml file.
For Example:<dependency>
<groupId>com.google.code.gson</groupId>
<artifactId>gson</artifactId>
<version>2.8.6</version>
</dependency>
import com.google.gson.Gson;
import com.google.gson.GsonBuilder;
import com.google.gson.annotations.Expose;
public class GsonExposeAnnotationTest {
public static void main(String[] args) {
Customer customer = new Customer("Dinesh", "CID124", new Integer(12));
Gson gson = new GsonBuilder().setPrettyPrinting().create();
System.out.println(gson.toJson(customer));
gson = new GsonBuilder().setPrettyPrinting().excludeFieldsWithoutExposeAnnotation().create();
System.out.println(gson.toJson(customer));
}
}
class Customer {
@Expose(serialize = true, deserialize = true)
public String customerName;
@Expose(serialize = true, deserialize = true)
public String customerId;
@Expose(serialize = false, deserialize = false)
public Integer totalAssets;
public Customer(String customerName, String customerId, Integer totalAssets) {
this.customerName = customerName;
this.customerId = customerId;
this.totalAssets = totalAssets;
}
}
Input:{"customerName": "Dinesh", "customerId": "CID124", "totalAssets": 12 }output: Only exposed fields are in the seen in the output after serialisation.{ "customerName": "Dinesh", "customerId": "CID124" }
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