在 PHP 中运行 shell_exec('which java') 不返回任何内容

Question

If I run

which java

from the command line I get the proper input (/usr/java/.../bin/java). However if I run it in a php script:

<?
  echo 'java. ' . shell_exec('which java');
  echo 'ls. ' . shell_exec('which ls');
?>

nothing gets printed out for which java but I get the proper results for which ls...

Answer 1

Two things were needed:

• the full path to the JVM (it wasn't set in the environment)
• " 2>&1" at the end of the command line.

So for example:

echo shell_exec('/usr/java/jdk6/bin/java -cp myJars.jar MyMainClass arg1 2>&1");

Answer 2

I just ran into this problem as well. I was trying to determine if the qrencode utility is installed on the (any) server, and if not then log/warn/exit gracefully.

Considering the program should always be in a standard path, I prefixed the which command with the likely locations of the binary, while still respecting that $PATH might be somehow defined on the system. I think you could use this approach with common Java paths, too:

shell_exec('PATH="$PATH:/bin:/sbin:/usr/bin:/usr/sbin:/usr/local/bin:/usr/local/sbin" '.
           'which qrencode');