How to get branch name while running azure pipeline?

I am trying to run below command through azure pipeline to get branch name but after execution getting HEAD.

Process process = Runtime.getRuntime().exec("git rev-parse --abbrev-ref HEAD");
    
    process.waitFor();

    BufferedReader reader = new BufferedReader(
            new InputStreamReader(process.getInputStream()));

    return reader.readLine();

I have tried below commands as well but no luck

• git branch | grep '*'
• git symbolic-ref --short HEAD

PS I am not using multi-branching pipeline and the requirements were to not use multi-branching.

If you are trying to get the branch that the build was triggered from there are some built in pipeline variables you can use without needing to write a script

Build.SourceBranch which will return something like refs/heads/main or refs/heads/feature/tools

Build.SourceBranchName which will return main or tools

you can use these in your YAML in various ways

As variables

$(Build.SourceBranch)
$(Build.SourceBranchName)

As expressions

variables: 
  - name: isMain
    value: $[eq(variables['Build.SourceBranch'], 'refs/heads/main')]
  - name: isMaster
    value: $[eq(variables['Build.SourceBranch'], 'refs/heads/master')]
  - name: isDevelop
    value: $[eq(variables['Build.SourceBranch'], 'refs/heads/develop')]
  - name: isFeature
    value: $[startsWith(variables['Build.SourceBranch'], 'refs/heads/feature/')]
  - name: isRelease
    value: $[startsWith(variables['Build.SourceBranch'], 'refs/heads/release/')]
  - name: isHotFix
    value: $[startsWith(variables['Build.SourceBranch'], 'refs/heads/hotfix/')]

As environment variables in a script. With environment variables . is replaced with _

trigger:
- none

pool:
  vmImage: ubuntu-latest

steps:
- task: PowerShell@2
  inputs:
    targetType: 'inline'
    script: |
      write-host $env:BUILD_SOURCEBRANCH
      write-host $env:BUILD_SOURCEBRANCHNAME
    pwsh: true

- task: Bash@3
  inputs:
    targetType: 'inline'
    script: |
      echo $BUILD_SOURCEBRANCH
      echo $BUILD_SOURCEBRANCHNAME

the easiest way to get what you desire is using the built-in variable: Build.SourceBranch or Build.SourceBranchName (if you only need the name, not ref)

https://learn.microsoft.com/en-us/azure/devops/pipelines/build/variables?view=azure-devops&tabs=yaml#build-variables-devops-services