The return value of php exec in linux cannot be negative.

Let's take a look at how to use the exec function.

Exec ()
Prototype:

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String exec (string command [, string array [, int return_var])

The exec () function is similar to system (). It also executes the given command, but does not output the result, but returns the last line of the result. Although it only returns the last line of the command result, the complete result can be obtained using the second parameter array by appending the result row by row to the end of the array. Therefore, if the array is not empty, we recommend that you use unset () to clear it before calling it. Only when the second parameter is specified can the third parameter be used to obtain the command execution status code.
Example:

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Exec ("/bin/ls-l "); Exec ("/bin/ls-l", $ res ); Exec ("/bin/ls-l", $ res, $ rc );

In the third parameter, how can I not receive negative numbers ??
Here & $ return_var is the return value of the program. At first, my answer is a negative number.
We usually write this in c.

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# Include <stdio. h> # Include <stdlib. h> Int main () { Printf ("^_^ n "); Return-5; }

This-5 is the return value, but it is written as 0 or 1.
Note: Many people write the main function as void main () in C code. This is actually not correct, so I won't go into details.
Compile the above code and run it in CMD. Then the output result is displayed. Enter "echo % ERRORLEVEL %" and press enter to view the program return value. This % ERRORLEVEL % indicates the return status of the program. In WIN, it can be a negative number.

, Php call is also normal.

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E: devphp535> php-r "exec('return.exe ', $ out, $ a); var_dump ($ );"

Int (-2)
However, in linux, it is always a positive number. It was initially suspected that it was a Permission problem. After chmod + x was used, the permission problem was ruled out.

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Exec ("/home/wwwroot/test/rtest. out 2> & 1", $ out, $ ); Var_dump ($ out, $ ); Array (1) {[0] => string (3) "^_^"} int (251)

It seems to be 256 + return val. We can see that a negative number is actually returned, but it is converted to a positive number.
Then I read the source code in standard/exec. c, but I didn't find any clues. It was very strange. I suddenly thought I forgot a step. I forgot to read the OS value returned by the program.
Echo $? Displays the launch status of the last command.

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-Bash-3.00 $ vi main. c -Bash-3.00 $ gcc-o./mm main. c -Bash-3.00 $ ll Total 48 Drwxr-xr-x 3 www 4096 May 4 2011 2011 Drwxr-xr-x 6 www 4096 Jun 23 2011 eoc -Rwxr-xr-x 1 www 7131 Feb 1 hello -Rw-r -- 1 www 3 Feb 1 :51 hello. c -Rw-r -- 1 www 99 Feb 1 :50 main. c -Rwxr-xr-x 1 www 4714 Feb 1mm Drwxr-xr-x 3 www 4096 Jun 24 2011 test -Bash-3.00 $./mm Pai_^ -Bash-3.00 $ echo $? 251 -Bash-3.00 $

In this way, you can see the value of exec returned to OS.
In linux, the returned value is of the unsigned type and returns a positive value. Therefore, it is also a positive value to pass to php. php is actually the value returned by the called exec.

OUT, maybe this is what linux requires. In the program, the Thai return value is 1 ~ 255, but you do not know this rule. However, it is not determined whether this is the rule in linux. Although the problem is very painful and of little significance, it can be left here for reference by people who encounter similar problems. However, there is no need to go further here. If you really want to figure it out, you can look at shell.