Add Head and Tail operations

src/core/config/OperationConfig.js

@@ -3196,7 +3196,69 @@ const OperationConfig = {
         outputType: "html",
         args: [
         ]
-    }
+    },
+    "Head": {
+        description: [
+            "Like the UNIX head utility.",
+            "<br>",
+            "Gets the first $Number of lines.",
+            "<br>",
+            "Optionally you can select all but the last $Number of lines.",
+            "<br>",
+            "The delimiter can be changed so that instead of lines, fields (i.e. commas) are selected instead.",
+        ].join("\n"),
+        run: StrUtils.runHead,
+        inputType: "string",
+        outputType: "string",
+        args: [
+            {
+                name: "Delimiter",
+                type: "option",
+                value: StrUtils.DELIMITER_OPTIONS
+            },
+            {
+                name: "Number",
+                type: "number",
+                value: 10,
+            },
+            {
+                name: "All but last $Number of lines",
+                type: "boolean",
+                value: false,
+            },
+        ]
+    },
+    "Tail": {
+        description: [
+            "Like the UNIX tail utility.",
+            "<br>",
+            "Gets the last $Number of lines.",
+            "<br>",
+            "Optionally you can select all lines after line $Number.",
+            "<br>",
+            "The delimiter can be changed so that instead of lines, fields (i.e. commas) are selected instead.",
+        ].join("\n"),
+        run: StrUtils.runTail,
+        inputType: "string",
+        outputType: "string",
+        args: [
+            {
+                name: "Delimiter",
+                type: "option",
+                value: StrUtils.DELIMITER_OPTIONS
+            },
+            {
+                name: "Number",
+                type: "number",
+                value: 10,
+            },
+            {
+                name: "Start from line $Number",
+                type: "boolean",
+                value: false,
+            },
+        ]
+    },
 };
 
 export default OperationConfig;

src/core/operations/StrUtils.js

@@ -537,6 +537,61 @@ const StrUtils = {
         return output;
     },
 
+    /**
+     * Head lines operation.
+     *
+     * @param {string} input
+     * @param {Object[]} args
+     * @returns {string}
+     */
+    runHead: function(input, args) {
+        let delimiter = args[0],
+            number = args[1],
+            allBut = args[2];
+
+        delimiter = Utils.charRep[delimiter];
+        let splitInput = input.split(delimiter);
+
+        return splitInput
+        .filter((line, lineIndex) => {
+            lineIndex += 1;
+
+            if (allBut) {
+                return lineIndex <= splitInput.length - number;
+            } else {
+                return lineIndex <= number;
+            }
+        })
+        .join(delimiter);
+    },
+
+    /**
+     * Tail lines operation.
+     *
+     * @param {string} input
+     * @param {Object[]} args
+     * @returns {string}
+     */
+    runTail: function(input, args) {
+        let delimiter = args[0],
+            number = args[1],
+            allBut = args[2];
+
+        delimiter = Utils.charRep[delimiter];
+        let splitInput = input.split(delimiter);
+
+        return splitInput
+        .filter((line, lineIndex) => {
+            lineIndex += 1;
+
+            if (allBut) {
+                return lineIndex >= number;
+            } else {
+                return lineIndex > splitInput.length - number;
+            }
+        })
+        .join(delimiter);
+    },
 };
 
 export default StrUtils;