Execute unix command in php

Question

In php,I have to find whether a directory exist. IF it exists not a problem (I will display the hyperlink for that using the dirname)

Here is the sample in which I need help.
dir_name is the directory name

$url = system(~'ls -d /home/myapps/rel/".$dir_name"');
        echo $url;(this does not work)
        if(preg_match("/No such/",$url)) {
                echo'Ther is no match'
        }
        else{
        }

In my code the if block is never executed.(it should execute if the directory does not exist) ;(

What's the ~ doing there? You also seem to have a wrong understanding of single and double quotes and variable interpolation. — deceze
– deceze ♦, Commented Sep 22, 2010 at 6:42

Arc · Accepted Answer · 2010-09-22 06:39:46Z

8

Why don't you use is_dir() ?

http://php.net/manual/en/function.is-dir.php

answered Sep 22, 2010 at 6:39

Arc

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codaddict · Accepted Answer · 2010-09-23 13:23:08Z

As others have told, is_dir is the right way to go.

I'll point out why your existing program does not work. This will be useful in cases when you want to run an external command and then parse its output.

You have a unwanted ~ in your call to system.
Variable interpolation does not happen in single quotes. So you need do something like:

system('ls -d /home/myapps/rel/'.$dir_name); or

system("ls -d /home/myapps/rel/$dir_name");
Even with the above changes it does not work because if the dir does not exist, ls issues the "....not found" error on stderr and not on stdout and system just returns the last line of the stdout. To fix this we need to redirect stderr of the command to stdout as:

system("ls -d /home/myapps/rel/$dir_name 2>&1");
You also need to remember that system returns only the last line of the output. In the current case if works, but in some other cases if the external command being run spits many lines of error/output system will not work and you'll have to use exec which allows you to collect entire output lines in an array. Something like:

exec("ls -d /home/myapps/rel/$dir_name 2>&1",$output_arr);
then you can search for your err string in the array $output_arr

So now you have the error message(if the dir does not exist) in $url and then check for the presence of string "No such".

Some more problems with the approach:

Some implementation of bash throw a different err message when you list for a non existing file. One I've seen is /foo/bar not found and this can cause your solution to break.
Also if the value of $dir_name contains the string No such ( weird but possible) your solution will break.

Tilman Koester · Accepted Answer · 2010-09-22 06:42:21Z

2

http://php.net/manual/en/function.file-exists.php

bool file_exists  ( string $filename  )

Returns true if file or directory exists. If you then need to find it out if its directory or file use is_dir()

answered Sep 22, 2010 at 6:42

Tilman Koester

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