append (Compute)

When To Use

Use append to concatenate a value to the end of a column's content, on every row of the table. Typical uses are adding a fixed suffix to build an identifier (e.g. appending _0 to a PnP address so it matches another source), merging two columns by appending $n (the content of column n) to another column, or adding empty placeholder columns so the table matches the column layout expected by mapping or by a tableJoin.

Because a table is serialized as semicolon-separated text, appending a value that contains ; effectively creates new columns to the right of the target column — a deliberate and widely used trick in real connectors.

Syntax

sources:
  diskDrives:
    type: wmi
    namespace: root\CIMv2
    query: SELECT Name, PNPDeviceID FROM Win32_DiskDrive
    computes:
      # Add a _0 suffix to the PnP address so that it matches the MPIO ID
      # PhysicalDiskName;PnPAddress_0;
    - type: append
      column: 2
      value: _0

Properties

Table Transformation Example

With column: 2 and value: _0:

Semicolon trick: since rows serialize as semicolon-separated text, - type: append with column: 2 and value: ;; on the row fan1;OK produces:

fan1;OK;;

which re-parses as 4 columns — two new empty columns now follow column 2. Real connectors use this to insert empty Status/StatusInformation placeholders (e.g. value: ;; in IpmiTool) or a constant extra column (value: ;joinValue in SmartMonLinux).

Recommended Pattern

• Keep a # Column1;Column2;... comment before and after each append that adds columns, so the evolving table layout stays readable.
• Use $n values to merge columns (e.g. append $5 to column 1 to build a composite identifier).
• Prefer append with ; padding over more complex sources when mapping simply needs extra empty columns.
• Quote values that start or end with spaces or contain YAML-significant characters: value: ' - '.

Common Mistakes

• Forgetting that column is 1-based: column: 1 targets the first column.
• Not realizing a ; in value changes the column count — every later compute and the mapping section must use the new indexes.
• Writing value: $5 expecting a literal $5: $n is interpreted as a column reference.
• Leaving an unquoted value that YAML truncates or mangles (a # inside the value starts a comment; leading/trailing spaces are stripped — quote such values: value: ' - ').

Community Examples

• WBEMGenLUN^[1]
• IpmiTool^[2]
• GenBatteryNT^[3]

From IpmiTool (adding empty columns with the semicolon trick):

  # Add empty Status and StatusInformation columns
  # Fan;SensorID;SensorName;StatusArray;StatusInformation;Location;FanSpeed;WarningThreshold;AlarmThreshold;
- type: append
  column: 3
  value: ;;