The EXEC function of PHP executes the bat script

The EXEC function in PHP executes the bat script, why can sometimes, sometimes fail??
BAT Script
@echo off
^
Ffmpeg-f concat-i c:^amp^apache2.4^htdocs^test^upload^2016-10-12^wu_1aurf2i6412121lrl4id1rqr1vgj0^filelist.txt-c Copy C:^amp^apache2.4^htdocs^test^upload^2016-10-12^57fdaea7c33d7.mpg
^
CD/
^
RD/S/q C:^amp^apache2.4^htdocs^test^upload^2016-10-12^wu_1aurf2i6412121lrl4id1rqr1vgj0
^
Echo Finished
^
PHP Code of execution:
$cmd = "C:ampapache2.4htdocstestupload2016-10-12wu_1aurf2i6412121lrl4id1rqr1vgj0merg.bat";
$cmd = "./.. /merg.bat ";
$res = EXEC ($cmd);
Var_dump ($res);

Reply content:

The EXEC function in PHP executes the bat script, why can sometimes, sometimes fail??
BAT Script
@echo off
^
Ffmpeg-f concat-i c:^amp^apache2.4^htdocs^test^upload^2016-10-12^wu_1aurf2i6412121lrl4id1rqr1vgj0^filelist.txt-c Copy C:^amp^apache2.4^htdocs^test^upload^2016-10-12^57fdaea7c33d7.mpg
^
CD/
^
RD/S/q C:^amp^apache2.4^htdocs^test^upload^2016-10-12^wu_1aurf2i6412121lrl4id1rqr1vgj0
^
Echo Finished
^
PHP Code of execution:
$cmd = "C:ampapache2.4htdocstestupload2016-10-12wu_1aurf2i6412121lrl4id1rqr1vgj0merg.bat";
$cmd = "./.. /merg.bat ";
$res = EXEC ($cmd);
Var_dump ($res);

View FFmpeg's logs to locate

Can be judged by status, repeated execution, and guaranteed results.

Thank you for your invitation. Whether the concurrent execution bat file has simultaneous operation of the same file, resulting in an error. Upstairs is also the wrong way to say.

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