Intercepting standard output / Passing application output (Shell/C/PHP) - php

Question

I am running a hybrid of shell script and a C application to allow execution as root. I am using it to do some conversions with FontForge from the website that is written in PHP. My problem is that when FontForge encounters some problems its spewing error information out to standard output. I am currently capturing that output and parsing it for keywords to generate some error messages.
Q: I am wondering if I can somehow redirect that output to some variable and pass it back to PHP for processing - as long as current solution works fine under browser, unfortunately when I run unit tests I get pages of failed glyph mapping information that does nothing but obscures the results. I would like to bypass std_out entirely.
I am not very very familiar with either C or shell scripting so please do not laugh :). Here is what I have:
PHP:
[...]
$new_path = exec("./convert_font " . $file . " " . $file2);
if (strpos($new_path, 'Save Failed') !== false) {
// throw exception or something
}
[...]
Script (convert_font):
#!/bin/bash
PATH=/usr/local/bin:$PATH
FONTFORGE_LANGUAGE=ff
export PATH FONTFORGE_LANGUAGE
if (test -f $1);
then
a=$(./pfb2otf $1 $2 2>&1)
fi
echo $a
C (pfb2otf):
#!/usr/bin/fontforge
//Opens file
Open($1);
Reencode("unicode");
//Makes conversion to otf
Generate($2+".otf");
//Prints the resulting name (if conversion is successful) to STD_OUT so I can capture it with my bash script to send back to PHP and consider operation successful to
Print($2+".otf");
Quit(0);

Answer 1

http://php.net/manual/en/function.exec.php
output
If the output argument is present, then the specified array will be filled with every line of output from the command. Trailing whitespace, such as \n, is not included in this array. Note that if the array already contains some elements, exec() will append to the end of the array. If you do not want the function to append elements, call unset() on the array before passing it to exec().
You can use the additional output parameter in your PHP Code to catch all stdout messages to an array. You can also redirect stderr to stdout in both perl and C
http://www.masaokitamura.com/2009/08/how-to-redirect-stderr-to-stdout-in-perl/
Hope this helps.

Answer 2

There are 3 things to note :
1) Your program writes probably errors on error output, to get them too you need to add 2>&1
$new_path = exec("./convert_font " . $file . " " . $file2 . ' 2>&1');
2) exec() returns only the last line of the command execution, the safest way to get your return values is to pass a second argument to your exec().
$return = array();
exec("./convert_font " . $file . " " . $file2 . ' 2>&1', $return);
You may note that $return is a multidimentional array with 1 line / entry. So to be sure you get your error into this array, you may do :
$new_path = implode("", $return);
3) do not forget to use escapeshellarg in case where one of your file has spaces (at least) or back quotes/parenthesis/dollar (...everything a shell can interpret).
$return = array();
exec("./convert_font " . escapeshellarg($file) . " " . escapeshellarg($file2) . ' 2>&1', $return);