Checking in jenkins whether an artefact exists for another job and branch - jenkins-pipeline

Question

I would like to copy an artefact depending on whether it exists in another job. I currently have the following code within a step:
script {
copyArtifacts filter: "dist.tar.gz",
projectName: 'Frontend/${BRANCH_NAME}',
selector: lastSuccessful(),
target: "./public"
}
Now, for example, I want something like this (I realise the syntax is wrong/stupid):
script {
if(file_exists('Frontend/${BRANCH_NAME}').lastSuccessful()) {
copyArtifacts filter: "dist.tar.gz",
projectName: 'Frontend/${BRANCH_NAME}',
selector: lastSuccessful(),
target: "./public"
}
}
So if there is a latest build for the frontend/${BRANCH_NAME}, I would like to execute what it says below. I could now try to perform a check via the browser URL, for example, but isn't there a more elegant solution to do this internally?
I am using a multibranch, thats the reason why I want handle it different.
Edit:
I guess I need to describe my problem a little better after reviewing Geralds suggested solution!
Thank you Gerald for your solution! Unfortunately, it doesn't really fit my problem. You check whether a certain file exists in a project in the branch.
What I need: There is a multi-branch pipeline in which an artefact is created in the respective branch pipeline (e.g. dist.tar.gz) and I would like to check whether this dist.tar.gz is available as an artefact and take the latest version of it.
I can certainly jump over the file system here, but my thought was whether this can be done directly via available methods in Jenkins.
With copyArtifacts, I can simply specify the project name and branch, and it finds the rest on its own. But if the file does not exist, it fails, for example. And finally, depending on the branch, the result is slightly different for my source project, so I need this check if a file exists within another project for a branch. As I said, I am referring to the pipeline and its result (=Artifact) and not to a file in the Git branch.
Edit 2:
Okay, a little progress:
I can definitely retrieve what the last successful build in the multipipeline was with the following code:
def jobName = "My folder/multipipeline/master".
def buildName = Jenkins.instance.getItemByFullName(jobName)
println "Job type: ${buildName.getClass()}"
println "Last success: ${buildName.getLastSuccessfulBuild()}"
println "All builds: ${buildName.getBuilds().collect{ it.getNumber()}}"
println "Last build: ${buildName.getLastBuild()}"
Then displays something like:
Job type: class org.jenkinsci.plugins.workflow.job.WorkflowJob
Last success: my folder/multipipeline/master/dev #21
All builds: [21, 20, 19, 18, 17]
Last build: my folder/multipipeline/master/dev #21
Now I should be able to access an artefact within the Jenkins instance or check if it exists at all

Answer 1

environment {
otherProjectWksp = '../other-project-with-Git-repo/'
otherProjectBranch = 'master'
otherProjectRemoteBranch = 'origin/master'
checkFileExists = 'README.md'
//checkFileExists = 'NOT_EXISTING' // for testing
fileExistsStatus = '-1'
}
stages {
stage('Check if file exists in other project\'s remote branch') {
steps {
dir( otherProjectWksp ) {
script {
fileExistsStatus = sh script: """
#!/bin/bash
git cat-file -e ${otherProjectRemoteBranch}:${checkFileExists} && echo ${checkFileExists} exists
""",
returnStatus: true
}
} // dir
echo "fileExistsStatus: ${fileExistsStatus}"
}
} // stage Check file existence
stage('Copy artifacts') {
when { expression { fileExistsStatus == '0' } }
steps {
echo "Copying artifacts..."
// ...
}
} // stage Copy artifacts
}
Console Output
...
[Pipeline] stage
[Pipeline] { (Check if file exists in other project's remote branch)
[Pipeline] dir
Running in /var/lib/jenkins/workspace/other-project-with-Git-repo
[Pipeline] {
[Pipeline] script
[Pipeline] {
[Pipeline] sh
+ git cat-file -e origin/master:README.md
+ echo README.md exists
README.md exists
[Pipeline] }
[Pipeline] // script
[Pipeline] }
[Pipeline] // dir
[Pipeline] echo
fileExistsStatus: 0
[Pipeline] }
[Pipeline] // stage
[Pipeline] stage
[Pipeline] { (Copy artifacts)
[Pipeline] echo
Copying artifacts...
...