Cocoa - Add some bytes at the end of a file

Question

I'm developing a Cocoa app that has to execute some terminal commands. One of these looks like:

printf "\xc5\x20\x00\x00" >> aFile.txt

I tried with NSTask (but I'm not sure how to split the arguments):

NSTask *task = [[NSTask alloc] init];
[task setLaunchPath:@"/usr/bin/printf"];
[task setArguments:[NSArray arrayWithObjects:@"\"\\xc5\\x20\\x00\\x00\"",
                                             @">>",
                                             @"aFile.txt", nil]];
[task launch];

All I get is:

printf: missing format character

So I think that ">>" is not a printf argument but an internal terminal command.

How can I simulate that command in Objective C?

score 4 · Answer 1 · answered Nov 07 '11 at 14:22

4

You may be interested in NSTask method:

- (void)setStandardOutput:(id)file

and in NSFileHandle methods:

+ (id)fileHandleForWritingAtPath:(NSString *)path
- (unsigned long long)seekToEndOfFile

answered Nov 07 '11 at 14:22

mouviciel

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Thank you very much, it works. But... there's a problem: i get "xc5x20x00x00" in the txt file instead of "√&", that i get if i run that command in the terminal – Oneiros Nov 07 '11 at 14:43

score 1 · Accepted Answer · answered Nov 07 '11 at 14:26

You're right, the >> token is a shell feature, not an argument to printf.

In this example, I'd probably not use the shell to do this, rather I would write the code to do it in Cocoa or plain C (with stdio.h).

However, to use the shell >> command, you can send the line to a shell process, which will interpret >> correctly.

NSTask *task = [[NSTask alloc] init];
[task setLaunchPath:@"/bin/bash"];
[task setArguments:[NSArray arrayWithObjects:@"-c",
                                             @"printf \"\xc5\x20\x00\x00\" >> aFile.txt",
                                             nil]];
[task launch];

Cocoa - Add some bytes at the end of a file

2 Answers2