Example

[lindex [split [file rootname [file tail [value root.name]]] "_"] end]

[lindex [split [file rootname [file tail [value root.name]]] "_"] 0]

[lindex [split [file rootname [file tail [value root.name]]] "_"] 1]

Example

2055_02400_v001.nk

[lindex [split [file rootname [file tail [value root.name]]] “_”] 0]
→　2055　→さらに 2 だけ抽出する

[string range <開始> <終了>]

[string range [lindex [split [file rootname [value root.name]] “_”] 0] 0 0]
2

[string range [lindex [split [file rootname [value root.name]] “_”] 0] 0 1]
20

[string range [lindex [split [file rootname [value root.name]] “_”] 0] 1 end]
055

[string range [lindex [split [file rootname [value root.name]] “_”] 0] 1 end-1]
05

Reference**:**

TCL FUNCTIONS IN TEXT NODE (https://www.gatimedia.co.uk/tcl-functions)