Add command line parameters to read and write file

README.md

@@ -23,15 +23,20 @@ sudo chmod +x /usr/local/bin/muenvsubst
 ## Usage
 
 ```
-Substitutes environment variables using one of the templating engines, as 
-envsubst does. 
+Substitutes environment variables using Inja templating engine, as envsubst 
+does. 
 
-USAGE: ./muenvsubst [ -h, --help <arg> ] [ -V, --version ] 
+USAGE: ./muenvsubst [ -h, --help <arg> ] [ -i, --in <arg> ] [ -o, 
+       --out <arg> ] [ -v, --version ] 
 
 OPTIONAL:
  -h, --help <arg> Print this help. 
 
- -V, --version    Output version information and exit
+ -i, --in <arg>   Input file 
+
+ -o, --out <arg>  Output file 
+
+ -v, --version    Output version information and exit
 ```
 
 ## Inja syntax

cli/main.cpp

@@ -13,20 +13,30 @@ int main(int argc, char** argv, char** envp)
 {
     bool showVersion = false;
     CmdLine cmd(argc, argv);
-    cmd.addHelp(
-        true, argv[0], "Substitutes environment variables using one of the templating engines, as envsubst does.");
-    cmd.addArgWithFlagAndName('V', "version", false, false, "Output version information and exit");
+    cmd.addHelp(true, argv[0], "Substitutes environment variables using Inja templating engine, as envsubst does.");
+    cmd.addArgWithFlagAndName('v', "version", false, false, "Output version information and exit");
+    cmd.addArgWithFlagAndName('i', "in", true, false, "Input file");
+    cmd.addArgWithFlagAndName('o', "out", true, false, "Output file");
     try {
         cmd.parse();
 
-        if (cmd.isDefined("-V")) {
+        if (cmd.isDefined("-v")) {
             cout << APP_VERSION << endl;
             return 0;
         }
 
-        auto tmpl = readAllInput();
-        cout << renderWithInja(tmpl, envp);
-
+        string tmpl;
+        if (cmd.isDefined("-i")) {
+            tmpl = readFile(cmd.value("-i"));
+        } else {
+            tmpl = readAllInput();
+        }
+        auto out = renderWithInja(tmpl, envp);
+        if (cmd.isDefined("-o")) {
+            writeFile(cmd.value("-o"), out);
+        } else {
+            cout << out;
+        }
     } catch (const HelpHasBeenPrintedException&) {
         return 0;
     } catch (const BaseException& x) {

lib/tools.cpp

@@ -1,8 +1,11 @@
 #include "tools.h"
 
 #include <algorithm>
+#include <filesystem>
+#include <fstream>
 #include <iostream>
 #include <iterator>
+#include <sstream>
 
 using namespace std;
 
@@ -25,6 +28,32 @@ std::string readAllInput()
     return string(it, end);
 }
 
+std::string readFile(const string& file)
+{
+    try {
+        if (!filesystem::exists(file))
+            throw runtime_error("File does not exists");
+        ifstream ifs(file, ios::in);
+        ifs.exceptions(ifs.exceptions() | ios::failbit | ios::badbit);
+        stringstream ss;
+        ss << ifs.rdbuf();
+        return ss.str();
+    } catch (const exception& e) {
+        throw runtime_error((stringstream() << "Cannot read file: \"" << file << "\". Error: " << e.what()).str());
+    }
+}
+
+void writeFile(const std::string& file, const std::string& content)
+{
+    try {
+        ofstream ofs(file, ios::out);
+        ofs.exceptions(ofs.exceptions() | ios::failbit | ios::badbit);
+        ofs << content;
+    } catch (const exception& e) {
+        throw runtime_error((stringstream() << "Cannot write file: \"" << file << "\". Error: " << e.what()).str());
+    }
+}
+
 vector<string> stringSplit(const string& s, const string& delimiter)
 {
     vector<string> res;

lib/tools.h

@@ -4,6 +4,8 @@
 #include <vector>
 
 std::string readAllInput();
+std::string readFile(const std::string& file);
+void writeFile(const std::string& file, const std::string& content);
 
 struct KeyValue {
     std::string key;