Calling C Executable using PHP

Question

I have a c file I've compiled with a executable called "run" And want to run it with a argv[1] of testfile.txt that is in the uploads directory.

This here seems to work, but I don't understand why.

exec(__DIR__ . '/run uploads/testfile.txt',$output);

C programs are run as such:

./run uploads/testfile.txt

Adding a dot to the beginning of the exec() command makes it not work, but I'm running an executable, not a file (not a file run), why does the first example work but the other doesn't?

This doesn't work but it should?

exec(__DIR__ . './run uploads/testfile.txt',$output);

Where ./run is the c executable, and argv[1] is in the uploads directory which is testfile.txt

geomagas · Accepted Answer · 2016-11-05 00:04:52Z

1

Suppose __DIR__=='/foo/bar'.

Then, __DIR__ . './run' would evaluate to /foo/bar./run which does not exist.

edited Nov 5, 2016 at 0:04

answered Nov 5, 2016 at 0:01

geomagas

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2 Comments

oekroek Over a year ago

So how would I fix it using the dot?

Barmar Over a year ago

@oekroek Leave out the dot, it's not needed.

Barmar · Accepted Answer · 2016-11-05 00:09:16Z

0

You only need the . when you're running a program without providing a pathname. If the program name doesn't contain /, the shell searches for the program in $PATH. By typing ./run, it tells it to look in the current directory rather than searching for it.

Since you're providing a full path to the program by prepending __DIR__, it won't search for the program. It's not necessary to insert . before the program name in this case, and it's resulting in an incorrect filename. It's adding . to the last directory in __DIR__, and that directory doesn't exist.

answered Nov 5, 2016 at 0:09

Barmar

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Comments

LotoLo · Accepted Answer · 2016-11-05 00:06:38Z

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The dot concatenates two strings.
__DIR__ is a magic constant which is your php file directory not slash-terminated (see php doc).
Suppose __DIR__ = my_dir, if you add a dot before run you'll get:

my_dir./run

edited Nov 5, 2016 at 0:06

answered Nov 5, 2016 at 0:00

LotoLo

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AbraCadaver · Accepted Answer · 2016-11-05 00:12:07Z

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exec(__DIR__ . './run uploads/testfile.txt',$output);

__DIR__ has no / at the end

So you will try to execute /home/me/project./run.

You could run /home/me/project/./run though for example. The dot . refers to the current directory.

edited Nov 5, 2016 at 0:12

AbraCadaver

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answered Nov 5, 2016 at 0:01

Tommos

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2 Comments

oekroek Over a year ago

I'm not sure what you mean by it has no / at the end?

LotoLo Over a year ago

if you directory name is my_dir then _DIR_ = my_dir and not my_dir/

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