# -*- d -*-

# smallest
# the smallest running program doing nothing
void main() {}

# hello world
# print a simple string on stdout
import std.stdio;
void main() { write("Hello World"); }

# argv
# access command line parameters (no segmentation fault accepted, nor silent exception, so some languages must explicitly check the presence of the argument)
import std.stdio;
void main(string[] a) { if(a.length>1) writeln(a[1]); }

# env
# access environment variable
import std.stdio,std.process;
void main() { writeln(getenv("HOME")); }

# test file exists
# return exit code error (non zero) if a file does not exist
import std.file;
int main() { return !exists("/etc/mtab"); }

# test file readable
# return exit code error (non zero) if a file is not readable
import std.stdio;
void main() { File("/etc/mtab"); }

# formatting
# print integers in a simple formatted string
import std.stdio;
void main() {
    int a=1,b=2;
    writeln(a," + ",b," = ",a+b);
}


# system
# call an external program and check the return value
import std.stdio,std.process;
void main() {
    if (system("false"))
        stderr.writeln("false failed");
    system("echo done");
}


# sed in place
# remove #-comments from a file (modifying the file, i.e. in place)
import std.file,std.regex;
void main(string[] a) {
    a[1].write(a[1].readText().replace(regex("#.*","g"),""));
}


# compile what must be
# find and compile .c files into .o when the .o is old or absent
import std.stdio,std.file,std.process;
void main() {
    foreach (c; listdir("","*.c")) {
        auto o = c[0..$-1]~'o';
        if (lastModified(o,0) < lastModified(c)) {
            writeln("compiling "~c~" to "~o);
            system("gcc -c -o '"~c~"' '"~o~"'");
        }
    }
}


# grep
# grep with -F -i -h handling, usage, grep'ing many files
import std.stdio,std.regex,std.getopt;
int main(string[] a) {
    bool h,F,i;
    getopt(a,"h",&h,"F",&F,"i",&i);
    if (a.length<2 || h) {
        writeln("usage: grep [-F] [-i] regexp [files...]");
        return 1;
    }
    auto e = F ? a[1].replace(regex(r"\W","g"),r"\$&") : a[1];
    foreach (f; a[2..$])
        foreach (l; File(f).byLine())
            if (!l.match(regex(e, i ? "i" : "")).empty)
                writeln(a.length>3 ? f~':'~l : l);
    return 0;
}