What exactly am I missing in executing find from C++?

Question

My effort is to use a piece of code in my program to find and copy certain files in my system.

The code I wrote meant to do that is:

void scan(int i)
{
pid_t parent = getpid();
pid_t pid = fork();

if (pid == -1)
{
    cout << "failed to fork" << endl;
    return;
}
else
{
    if(pid > 0)
    {
        int status;
        waitpid(pid, &status, 0);
    }
    else
    {
        if(i == 0)
        {
            execl("/usr/bin/find","find", "/", "-name", "'*.mp3'","-exec","cp","{}","/home/pi/Music","\\;",(char *)0);
            _exit(EXIT_FAILURE);
        }
    }
}

return; }

Nevertheless, the system returns this:

find: missing argument to `-exec'

How exactly can I correct my execl command to execute this shell command:

find / -name '*.mp3' -exec cp {} /home/pi/Music \;

Note that you're not executing a "Bash command" here; `find` exists independently of Bash. — Oliver Charlesworth, May 14 '17 at 21:18
`cout << "failed to fork" << endl` a string literal is not a valid operand for `<<` in C. — wildplasser, May 14 '17 at 21:20
1) That's not C code 2) Your question is not related to C or C++. 3) Not related to programming. — too honest for this site, May 14 '17 at 21:20
@FreudianSlip - The first param to `execl` is the executable path. The rest are the args; `argv[0]` is, by convention, the name of the executable. — Oliver Charlesworth, May 14 '17 at 21:21
@OliverCharlesworth: It is about the Unix `find` command, which is not related to programming in the context of this site. — too honest for this site, May 14 '17 at 21:23
@AndrewHenle - If you omit one of the \ then it won't compile... — Oliver Charlesworth, May 14 '17 at 21:24
@Olaf - if I use only the find command written above, it works fine. Only problem is to convert that to execl format. So I would personally say this is related to pragramming. — Zbyněk Jakš, May 14 '17 at 21:25
@OliverCharlesworth True. I forgot that. I was having way too much trouble trying to get one backslash in code ticks to show up properly. — Andrew Henle, May 14 '17 at 21:26
I'll delete my wrong suggestion above so as not to confuse - sorry for the bum steer. Found this - it may help : http://stackoverflow.com/questions/12596839/how-to-call-execl-in-c-with-the-proper-arguments — FreudianSlip, May 14 '17 at 21:27
Consider using the new [fileystem](http://en.cppreference.com/w/cpp/header/experimental/filesystem) library if your compiler is modern enough. — rwols, May 14 '17 at 21:34
@ZbyněkJakš: There is nothing about "execl format". You seems to have understood arguments are given one per parameter. So it **is** a problem with the syntax of `find` arguments you need to understand. "if I use only the find command written above" does not say anything else than you just used a pattern you don't really understand. — too honest for this site, May 14 '17 at 21:40
@Olaf true. Since this is my very first question here. Would you please recommend what should've be done differently when asking this question for future purposes? Thank you :) — Zbyněk Jakš, May 14 '17 at 21:47
@Olaf Don't get borderline (rude), I've been badly experiencing that ya know ;-) — πάντα ῥεῖ, May 14 '17 at 22:19
@πάνταῥεῖ: OP asked for a tip what to do to ask better questions. Doing research before asking is the best way. The first address of research would be the manuals/documentation. So what's rude about this? I intentionally did not just write "RTFM" which some people consider being rude. If in doubt, assume the worst is a really bad attitude (I don't mean you). — too honest for this site, May 14 '17 at 22:33

Oliver Charlesworth · Answer 1 · 2017-05-14T21:31:05.173

2

TL;DR - Remove the \\ before the ;.

In the context of a shell, a command is interpreted before the individual arguments being passed to the find executable. ; is a special character, so needs escaping in order to be interpreted as a literal (as it's a special character) - find actually only needs ;.

However, you're not passing the arguments on the shell - execl passes the arguments directly to the target executable. So there's no need to escape it.

As pointed out by @AndrewHenle in comments below, you'll also need to remove both the ' from '*.mp3' for similar reasons.

edited May 14 '17 at 21:31

answered May 14 '17 at 21:30

Oliver Charlesworth

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You beat me to it. I figured it had to be something to do with the backslashes. The `'` chars in the `-name` argument will probably muck up `find`'s file name globbing, too. – Andrew Henle May 14 '17 at 21:31
@AndrewHenle - Good call! Have updated answer. – Oliver Charlesworth May 14 '17 at 21:35
solved, thank you for help – Zbyněk Jakš May 14 '17 at 21:49

score 0 · Answer 2 · answered May 14 '17 at 21:32

0

There is no Bash in sight, despite your question title. Yet you are using Bash-style quoting.

"'*.mp3'"

Your find will find nothing unless you have files with single quotation marks in their names. Use "*.mp3".

"\\;"

find requires a single semicolon to terminate the -exec arguments. \; is the Bash way to use a literal semicolon. Normally ; is a reserved character in Bash. Use a simple ";".

answered May 14 '17 at 21:32

n. m. could be an AI

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Thank you very much, problem solved. – Zbyněk Jakš May 14 '17 at 21:37

What exactly am I missing in executing find from C++?

2 Answers2