To check if a folder exists or not, and to write to the file

build.gradle

//To check if a folder exists or not, and to write to the file

// Create a File object representing the folder 'A/B'
def folder = new File( 'A/B' )

// If it doesn't exist
if( !folder.exists() ) {
  // Create all folders up-to and including B
  folder.mkdirs()
}

// Then, write to file.txt inside B
new File( folder, 'file.txt' ).withWriterAppend { w ->
  w << "Some text\n"
}

Not sure which version of gradle you're using here, but I confirm the folder.exists() doesn't work on gradle 7.1 with plugin 4.2.1. Always false no matter what