Writing short utilities in other languages

You can of course write short command-line utilities and scripts to automate tasks in almost any programming language.

C / C++

C++ Reference

Compiling a C++ program in UNIX / Linux

"Hello World" program

 edit prog.cxx
 g++ prog.cxx

This creates a binary executable file called a.out
To make the output a file called prog do this:

 g++ prog.cxx -o prog

You may need to: chmod +x prog
Then run:

 prog (args)

g++ - GNU C++ compiler
gcc - GNU C-only compiler
CC - Sun C++ compiler
cc - Sun C-only compiler
cxx - DEC C++ compiler

Accessing the command-line from C++

In a HLL, calling other programs (and access to the command-line in general) is usually more awkward than in a command-line-oriented script.

Example 1

In C/C++ you use the system() call:

  #include <stdlib.h>

  main()
  {
   system ( "rm file7.txt" );
  }

which is more complex than the Shell:

  rm file7.txt

You also have to compile the program, and keep track of 2 files - the source and the binary. In Shell, there is only 1 file.

Example 2

Also, the above is alright if filenames are static. But consider where the file name is variable. In Shell:

  for i in 96 97 98 99 00
  do
   rm $i.log $i.txt
  done

In C++ this is much more complex:

  #include <stdio.h>
  #include <stdlib.h>

  main()
  {
   char buf [ 30 ];

   for ( int i=96; i<=99; i++ )
   {
    sprintf ( buf, "rm %d.log %d.txt", i, i );
    system ( buf );
   }

   system ( "rm 00.log 00.txt" );
  }

Question

And if you want to get directory listings Shell is much easier.
Q. How would you code the following Shell script in C++?

  for i in */*doc */*xls
  do
   cp $i $HOME/backups/$i
  done

Environment variables

Access to environment variables is usually a bit more awkward in the HLL:

  #include <stdlib.h>

  char *homestring = getenv ( "HOME" );

Advantages and Disadvantages of C++ compared to Shell

Disadvantages of C++ compared to shell (for writing short utilities):
1. Constructing command-lines in general, with environment variables, variable and wildcard filenames, and piping and redirection, is more cumbersome.
2. The programs have to be recompiled any time you move to a new system.
Advantages of C++ compared to shell:
1. Execution speed much faster.
2. High-level programming features - types, data structures, arrays, object-oriented classes with inheritance, class libraries.
  Support for GUIs, threads, etc.
  Shell is only useful for simple programs.

GUI in Shell

There are some clever projects to get some limited GUI support into Shell.

Packages to allow shell scripts pop up GUI dialogs (and retrieve results):

Color selection dialog in Zenity, launched from Shell, return value captured in Shell.
Usage like:
COLOR=`zenity --color-selection --show-palette`
Screenshot from here.

Other HLLs

Of course, Java and a range of other HLLs could be used for the tasks above.

Java

Perl

Interpreted language. Direct access to command-line. More advanced than Shell.

Perl

PHP

PHP can be used as a command-line scripting language.

Can use a mix

I tend to write my short utilities in Shell.
For more complex utilities, I use C++.
For simpler utilities I try to express them as aliases.

Often, I use both HLL and Shell:

I surround a C++ utility with a small Shell wrapper that prepares the filenames and environment variables, calls the C++ program, and then possibly does some processing of the output.
In some of my online scripts, I surround Shell utilities with C++ character by character input processing for security.

A hierarchy of languages

I want to customise my system, and automate many tasks.
Like any programmer, I am always starting to write programs. How should I approach writing small utilities?

Very simple customisation - Check out program preferences or command-line arguments.
1-liner utilities - aliases
Command-line utilities with some logic - Shell
Complex command-line utilities - Perl (or other)
Small applications doing lots of calculations - C++ (or HLL of your choice)
Complex applications - Before investing a load of time in writing it yourself, maybe look online for freeware, shareware, or even (gasp) something you might buy.