Command-Line Tools in Objective-C

$ clang -fobjc-arc -Wall -Wextra -framework Foundation -o shelf shelf.m

#import <Foundation/Foundation.h>

int main(int argc, const char *argv[]) {
    @autoreleasepool {
        NSProcessInfo *info = NSProcessInfo.processInfo;
        NSArray<NSString *> *args = info.arguments;      // args[0] is the program name
        NSDictionary<NSString *, NSString *> *env = info.environment;

        NSString *home = env[@"SHELF_HOME"] ?: @"(unset)";
        printf("process name : %s\n", info.processName.UTF8String);
        printf("argc / count : %d / %lu\n", argc, (unsigned long)args.count);
        printf("SHELF_HOME   : %s\n", home.UTF8String);
        for (NSUInteger i = 1; i < args.count; i++) {
            printf("arg[%lu]      : %s\n", (unsigned long)i, args[i].UTF8String);
        }
        if (args.count < 2) {
            fprintf(stderr, "usage: %s <command> [options]\n", argv[0]);
            return 64;  // EX_USAGE from <sysexits.h>
        }
    }
    return 0;
}

$ SHELF_HOME=/srv/shelf ./args list --all "Dune Messiah"
process name : args
argc / count : 4 / 4
SHELF_HOME   : /srv/shelf
arg[1]      : list
arg[2]      : --all
arg[3]      : Dune Messiah
$ ./args
usage: ./args <command> [options]
$ echo $?
64

#import <Foundation/Foundation.h>

int main(void) {
    @autoreleasepool {
        NSUserDefaults *defaults = NSUserDefaults.standardUserDefaults;
        // Defaults used when neither the command line nor a preferences file sets a key.
        [defaults registerDefaults:@{ @"limit": @20, @"title": @"", @"verbose": @NO }];

        NSInteger limit = [defaults integerForKey:@"limit"];
        NSString *title = [defaults stringForKey:@"title"];
        BOOL verbose = [defaults boolForKey:@"verbose"];
        NSArray *tags = [defaults arrayForKey:@"tags"];

        printf("limit=%ld title='%s' verbose=%s tags=%s\n", (long)limit, title.UTF8String,
               verbose ? "YES" : "NO", tags ? tags.description.UTF8String : "(none)");
    }
    return 0;
}

$ ./defaults
limit=20 title='' verbose=NO tags=(none)
$ ./defaults -limit 5 -title "Dune Messiah" -verbose YES
limit=5 title='Dune Messiah' verbose=YES tags=(none)
$ ./defaults list -limit 7 extra
limit=7 title='' verbose=NO tags=(none)
$ ./defaults -tags '(sci-fi,classic)'
limit=20 title='' verbose=NO tags=(
    "sci-fi",
    classic
)

#import <Foundation/Foundation.h>
#include <getopt.h>
#include <sysexits.h>

static void usage(FILE *to) {
    fputs("usage: shelf list [-n|--limit N] [-t|--title TEXT] [-v|--verbose]\n"
          "       shelf --help | --version\n", to);
}

int main(int argc, char *argv[]) {
    @autoreleasepool {
        static const struct option longopts[] = {
            { "limit",   required_argument, NULL, 'n' },
            { "title",   required_argument, NULL, 't' },
            { "verbose", no_argument,       NULL, 'v' },
            { "help",    no_argument,       NULL, 'h' },
            { "version", no_argument,       NULL, 'V' },
            { NULL, 0, NULL, 0 }
        };

        long limit = 20;
        NSString *title = nil;
        BOOL verbose = NO;
        int c;
        while ((c = getopt_long(argc, argv, "n:t:vhV", longopts, NULL)) != -1) {
            switch (c) {
                case 'n': {
                    char *end = NULL;
                    limit = strtol(optarg, &end, 10);
                    if (*optarg == '\0' || *end != '\0' || limit < 1) {
                        fprintf(stderr, "shelf: invalid --limit '%s'\n", optarg);
                        return EX_USAGE;
                    }
                    break;
                }
                case 't': title = [NSString stringWithUTF8String:optarg]; break;
                case 'v': verbose = YES; break;
                case 'h': usage(stdout); return EX_OK;
                case 'V': puts("shelf 1.0.0"); return EX_OK;
                default:  usage(stderr); return EX_USAGE;   // getopt_long already printed the reason
            }
        }

        if (optind >= argc || strcmp(argv[optind], "list") != 0) {
            usage(stderr);
            return EX_USAGE;
        }
        printf("list: limit=%ld title=%s verbose=%s\n", limit, title ? title.UTF8String : "(any)",
               verbose ? "yes" : "no");
    }
    return EX_OK;
}

$ ./shelf list --limit 5 --title Dune -v
list: limit=5 title=Dune verbose=yes
$ ./shelf --limit 0 list; echo $?
shelf: invalid --limit '0'
64
$ ./shelf --bogus; echo $?
shelf: unrecognized option `--bogus'
usage: shelf list [-n|--limit N] [-t|--title TEXT] [-v|--verbose]
       shelf --help | --version
64

#import <Foundation/Foundation.h>

int main(void) {
    @autoreleasepool {
        NSFileHandle *in  = NSFileHandle.fileHandleWithStandardInput;
        NSFileHandle *out = NSFileHandle.fileHandleWithStandardOutput;
        NSFileHandle *err = NSFileHandle.fileHandleWithStandardError;

        // Read all of stdin (until EOF), one title per line.
        NSError *error = nil;
        NSData *data = [in readDataToEndOfFileAndReturnError:&error];
        if (data == nil) {
            NSString *msg = [NSString stringWithFormat:@"shelf: cannot read stdin: %@\n", error.localizedDescription];
            [err writeData:[msg dataUsingEncoding:NSUTF8StringEncoding] error:NULL];
            return 74;  // EX_IOERR
        }
        NSString *text = [[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding];
        if (text == nil) {
            [err writeData:[@"shelf: input is not valid UTF-8\n" dataUsingEncoding:NSUTF8StringEncoding] error:NULL];
            return 65;  // EX_DATAERR
        }

        NSUInteger n = 0;
        for (NSString *line in [text componentsSeparatedByString:@"\n"]) {
            if (line.length == 0) continue;
            n++;
            NSString *row = [NSString stringWithFormat:@"%2lu. %@\n", (unsigned long)n, line];
            if (![out writeData:[row dataUsingEncoding:NSUTF8StringEncoding] error:&error]) {
                return 74;  // e.g. EPIPE when the reader has gone away
            }
        }
    }
    return 0;
}

$ printf 'Dune\nHyperion\n' | ./fh
 1. Dune
 2. Hyperion
$ printf '\xff\n' | ./fh; echo $?
shelf: input is not valid UTF-8
65

#import <Foundation/Foundation.h>

int main(void) {
    @autoreleasepool {
        NSTask *task = [[NSTask alloc] init];
        task.executableURL = [NSURL fileURLWithPath:@"/usr/bin/sort"];
        task.arguments = @[@"-f"];

        NSPipe *toChild = [NSPipe pipe];
        NSPipe *fromChild = [NSPipe pipe];
        task.standardInput = toChild;
        task.standardOutput = fromChild;
        task.standardError = NSFileHandle.fileHandleWithStandardError;

        NSError *error = nil;
        if (![task launchAndReturnError:&error]) {
            fprintf(stderr, "shelf: cannot launch sort: %s\n", error.localizedDescription.UTF8String);
            return 127;
        }
        [toChild.fileHandleForWriting writeData:[@"hyperion\nDune\nemma\n" dataUsingEncoding:NSUTF8StringEncoding] error:NULL];
        [toChild.fileHandleForWriting closeAndReturnError:NULL];   // EOF for the child

        // Read before waiting: a full pipe would otherwise block the child forever.
        NSData *sorted = [fromChild.fileHandleForReading readDataToEndOfFileAndReturnError:NULL];
        [task waitUntilExit];

        fwrite(sorted.bytes, 1, sorted.length, stdout);
        if (task.terminationReason == NSTaskTerminationReasonUncaughtSignal) {
            fprintf(stderr, "sort killed by signal %d\n", task.terminationStatus);
            return 128 + task.terminationStatus;
        }
        return task.terminationStatus;
    }
}

$ ./task
Dune
emma
hyperion

#import <Foundation/Foundation.h>
#include <signal.h>

static dispatch_source_t makeSignalSource(int signo, dispatch_block_t handler) {
    signal(signo, SIG_IGN);   // the default action must be off, or the process dies first
    dispatch_source_t src =
        dispatch_source_create(DISPATCH_SOURCE_TYPE_SIGNAL, (uintptr_t)signo, 0, dispatch_get_main_queue());
    dispatch_source_set_event_handler(src, handler);
    dispatch_resume(src);
    return src;
}

int main(void) {
    @autoreleasepool {
        __block int ticks = 0;

        dispatch_source_t timer =
            dispatch_source_create(DISPATCH_SOURCE_TYPE_TIMER, 0, 0, dispatch_get_main_queue());
        dispatch_source_set_timer(timer, DISPATCH_TIME_NOW, 1 * NSEC_PER_SEC, 100 * NSEC_PER_MSEC);
        dispatch_source_set_event_handler(timer, ^{
            printf("shelfd: overdue-loan check %d\n", ++ticks);
            fflush(stdout);
        });
        dispatch_resume(timer);

        dispatch_source_t term = makeSignalSource(SIGTERM, ^{
            printf("shelfd: SIGTERM, shutting down after %d checks\n", ticks);
            fflush(stdout);
            exit(0);
        });
        dispatch_source_t hup = makeSignalSource(SIGHUP, ^{
            printf("shelfd: SIGHUP, reloading configuration\n");
            fflush(stdout);
        });
        (void)term; (void)hup;   // keep the sources alive for the life of the process

        dispatch_main();         // never returns; or [[NSRunLoop mainRunLoop] run]
    }
}

$ ./shelfd &
shelfd: overdue-loan check 1
shelfd: overdue-loan check 2
shelfd: overdue-loan check 3
$ kill -HUP %1
shelfd: SIGHUP, reloading configuration
shelfd: overdue-loan check 4
$ kill -TERM %1
shelfd: SIGTERM, shutting down after 4 checks

#import <Foundation/Foundation.h>

int main(void) {
    @autoreleasepool {
        NSTask *task = [[NSTask alloc] init];
        task.executableURL = [NSURL fileURLWithPath:@"/bin/sleep"];
        task.arguments = @[@"1"];

        __block BOOL finished = NO;
        __block int status = -1;
        task.terminationHandler = ^(NSTask *t) {
            // Runs on a background queue; hop to the main queue to touch main-thread state.
            int s = t.terminationStatus;
            dispatch_async(dispatch_get_main_queue(), ^{ status = s; finished = YES; });
        };
        NSError *error = nil;
        if (![task launchAndReturnError:&error]) return 127;

        NSRunLoop *loop = NSRunLoop.currentRunLoop;
        while (!finished && [loop runMode:NSDefaultRunLoopMode beforeDate:NSDate.distantFuture]) {}
        printf("child exited with %d\n", status);
        return status;
    }
}

$ ./async
child exited with 0

$ clang -fobjc-arc -framework Foundation -arch arm64 -arch x86_64 -o shelf shelf.m
$ lipo -info shelf
Architectures in the fat file: shelf are: x86_64 arm64
$ otool -L shelf
shelf:
	/System/Library/Frameworks/Foundation.framework/Versions/C/Foundation (compatibility version 300.0.0, current version 5027.0.69)
	/usr/lib/libobjc.A.dylib (compatibility version 1.0.0, current version 228.0.0)
	/usr/lib/libSystem.B.dylib (compatibility version 1.0.0, current version 1359.0.0)

include $(GNUSTEP_MAKEFILES)/common.make

TOOL_NAME = shelf
shelf_OBJC_FILES = shelf.m

include $(GNUSTEP_MAKEFILES)/tool.make

$ . /usr/share/GNUstep/Makefiles/GNUstep.sh
$ make

$ clang $(gnustep-config --objc-flags) shelf.m $(gnustep-config --base-libs) -o shelf