Nginx log how to output a variable

Code is PHP, running on Nginx, part is the function of sending mail
In order to facilitate debugging, want to output a variable to see,
But do not know where to output, how to output?
Node can directly console.log (), but how does the PHP output on Nginx?
Online said to change the log format, also useful echo?
Not very clear, can be directly echo? So where's the output?
Would you please give us a hint

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Code is PHP, running on Nginx, part is the function of sending mail
In order to facilitate debugging, want to output a variable to see,
But do not know where to output, how to output?
Node can directly console.log (), but how does the PHP output on Nginx?
Online said to change the log format, also useful echo?
Not very clear, can be directly echo? So where's the output?
Would you please give us a hint

Nginx logging is not the use of PHP to output, you should be to modify the nginx/conf/ngnix.conf file
Change the format after Log_format, different parameters corresponding to different values you can look at the

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