How can i add two fields which contains string value and store it in a new field

[Vishnu_mk (Vishnu)]

For ex:
name: Vishnu
surname_filed : mk

I want a to combine this to filed and in a new field

Name: Vishnu mk

[logger (Malte Leek)]

filter {
mutate {
add_field => { "new_field" => "%{name} %{surname}" }
}
}

this should work. or you look at the mutate filter and have a look at the great options. maybe there is something thats suites you better. like the merge option.

Mutate filter plugin | Logstash Reference [8.11] | Elastic

[Vishnu_mk (Vishnu)]

How can i add field in ingest pipeline:
PUT ingest/pipeline/abc7
{
"description" : "fscrawler res2",
"processors" : [
{
"grok": {
"field": "content",
"patterns": ["(^|\s)(?(\+\d{1,3}[- ]?)?\d{10})($|\s)"]
}
},
{
"grok": {
"field": "path.virtual",
"patterns": ["%{DATA:name1} %{DATA:surname}\%{GREEDYDATA:remaining}"]
}
}

]

This is my code i want to murge name1 and surname filed

[logger (Malte Leek)]

You are talking about elasticsearch and not logstash.

But have a look at this.
https://www.elastic.co/guide/en/elasticsearch/reference/current/accessing-data-in-pipelines.html

there you can access fields with the set parameter.