The return value of php exec cannot be negative in Linux_PHP Tutorial

The return value of php exec in Linux cannot be a negative number. Friends in need can refer to it.

Let’s first learn about how to use the exec function

exec()
Prototype:

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

代码如下	复制代码
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, using the second parameter array can get the complete result by appending the results line by line to the end of the array. So if the array is not empty, it is best to use unset() to clear it before calling it. Only when the second parameter is specified, the third parameter can be used to obtain the status code of command execution.
Example:

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exec("/bin/ls -l" );

代码如下	复制代码
exec("/bin/ls -l"); exec("/bin/ls -l", $res); exec("/bin/ls -l", $res, $rc);

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

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

The third parameter, why can’t it receive negative numbers??
The &$return_var here is the program return value. At first, my answer was that it can be a negative number. Generally in C language we would write like this

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#include #include int main() {     printf("^_^n");     return -5; }

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#include

#include
int main()
{

Printf("^_^n");

Return -5;

}

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

This -5 is the return value, but it is customary to write it as 0 or 1.
Note: Many people write the main function as void main() in their C code. This is actually wrong, so I won’t go into details.

After compiling the above code, run it under CMD, and then you can see the output result. Then, enter "echo %ERRORLEVEL%", press Enter, and you can see the return value of the program. This %ERRORLEVEL% represents the return status of the program. It is true that it can be a negative number under WIN

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

, php calls are also normal.

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

int(-2) But under Linux, it is always a positive number. At first I suspected it was a permissions issue. After using chmod +x, the permissions issue was eliminated.

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

It looks like 256+return val. You can see that a negative number is actually returned, but it is converted into a positive number.
Then I looked at the source code in standard/exec.c, and found no clues. It was very strange, and suddenly I realized that I had forgotten a step. Forgot to look at the value returned by the program to the OS.
You can use echo $? to display the status of the last command.

-rwxr-xr-x 1 www www 7131 Feb 1 12:47 hello -rw-r--r-- 1 www www 3 Feb 1 12:51 hello.c

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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 www 4096 May  4  2011 2011 drwxr-xr-x  6 www www 4096 Jun 23  2011 eoc -rwxr-xr-x  1 www www 7131 Feb  1 12:47 hello -rw-r--r--  1 www www    3 Feb  1 12:51 hello.c -rw-r--r--  1 www www   99 Feb  1 12:50 main.c -rwxr-xr-x  1 www www 4714 Feb  1 12:51 mm drwxr-xr-x  3 www www 4096 Jun 24  2011 test -bash-3.00$ ./mm ^_^ -bash-3.00$ echo $? 251 -bash-3.00$

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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 www 4096 May 4 2011 2011

drwxr-xr-x 6 www www 4096 Jun 23 2011 eoc

-rw-r--r-- 1 www www 99 Feb 1 12:50 main.c -rwxr-xr-x 1 www www 4714 Feb 1 12:51 mm

drwxr-xr-x 3 www www 4096 Jun 24 2011 test

-bash-3.00$ ./mm ^_^ -bash-3.00$ echo $? 251 -bash-3.00$ This way you can see what value exec returns to the OS. Under Linux, this return value is an unsigned type and returns a positive number, so it is also a positive number when passed to PHP. PHP is actually the value returned by the exec call. OUT, maybe this is how Linux stipulates. The return value in the program is in the range of 1~255, but I don’t know this rule. However, it has not yet been determined whether this is the case in Linux. Although the question is painful and of little significance, it can be left here for reference by people who encounter similar problems. But there is no need to go into details here. If you really want to understand it thoroughly, you can take a look at the shell

http://www.bkjia.com/PHPjc/632189.htmlwww.bkjia.comtruehttp: //www.bkjia.com/PHPjc/632189.htmlTechArticleThe return value of php exec cannot be a negative number in Linux. Friends in need can refer to it. Let’s first learn about how to use the exec function exec() prototype: The code is as follows Copy the code st...