implement "mem" command into LAMMPS shell to print current and max memory use

doc/src/Tools.rst

@@ -502,6 +502,7 @@ regular LAMMPS commands:
    clear_history  wipe out the current command history list
    pwd            print current working directory
    cd <directory> change current working directory (same as pwd if no directory)
+   mem            print current and maximum memory usage
    \|<command>     execute <command> as a shell command and return to the command prompt
    exit           exit the LAMMPS shell cleanly (unlike the "quit" command)
 

tools/lammps-shell/README

@@ -89,6 +89,7 @@ regular LAMMPS commands:
 - clear_history  wipe out the current command history list
 - pwd            print current working directory
 - cd <directory> change current working directory (same as pwd if no directory)
+- mem            print current and maximum memory usage
 - |<command>     execute <command> as a shell command and return to the command prompt
 - exit           exit the LAMMPS shell cleanly (unlike the "quit" command)
 

tools/lammps-shell/lammps-shell.cpp

@@ -463,6 +463,7 @@ static void init_commands()
     commands.push_back("exit");
     commands.push_back("pwd");
     commands.push_back("cd");
+    commands.push_back("mem");
     commands.push_back("history");
     commands.push_back("clear_history");
 
@@ -562,6 +563,13 @@ static int shell_cmd(const std::string &cmd)
         lammps_command(lmp, shellcmd.c_str());
         free(text);
         return 0;
+    } else if (words[0] == "mem") {
+        double meminfo[3];
+        lammps_memory_usage(lmp,meminfo);
+        std::cout << "Memory usage.  Current: " << meminfo[0] << " MByte, "
+                  << "Maximum : " << meminfo[2] << " MByte\n";
+        free(text);
+        return 0;
     } else if (words[0] == "history") {
         free(text);
         HIST_ENTRY **list = history_list();