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PHP exec() обрезает вывод stdout/output

7 Окт 2020
Ф-ция PHP exec() обрезает вывод output (результат выполнения stdout).
В моем случае нужно было получить JSON от внешней программы:
$lastLine = exec('/path/my_command.sh', $outputLines, $exitCode);
В результате переменные $lastLine и $outputLines содержали обрезанную JSON строку.
Причина была в том, что stdout вывод не помещается в установленный лимит в опции output_buffering:
cat /etc/php/7.4/cli/php.ini | grep output_buffering
output_buffering = 4096
Решение
Увеличить output_buffering или писать вывод в файл:
exec('/path/my_command.sh > /tmp/output.json', null, $exitCode);
$json = file_get_contents('/tmp/output.json');
// unlink('/tmp/output.json');
Документация output_buffering из php.ini:
; Output buffering is a mechanism for controlling how much output data
; (excluding headers and cookies) PHP should keep internally before pushing that
; data to the client. If your application's output exceeds this setting, PHP
; will send that data in chunks of roughly the size you specify.
; Turning on this setting and managing its maximum buffer size can yield some
; interesting side-effects depending on your application and web server.
; You may be able to send headers and cookies after you've already sent output
; through print or echo. You also may see performance benefits if your server is
; emitting less packets due to buffered output versus PHP streaming the output
; as it gets it. On production servers, 4096 bytes is a good setting for performance
; reasons.
; Note: Output buffering can also be controlled via Output Buffering Control
; functions.
; Possible Values:
; On = Enabled and buffer is unlimited. (Use with caution)
; Off = Disabled
; Integer = Enables the buffer and sets its maximum size in bytes.
; Note: This directive is hardcoded to Off for the CLI SAPI
; Default Value: Off
; Development Value: 4096
; Production Value: 4096
; Ссылка
output_buffering = 4096
; Transparent output compression using the zlib library
; Valid values for this option are 'off', 'on', or a specific buffer size
; to be used for compression (default is 4KB)
; Note: Resulting chunk size may vary due to nature of compression. PHP
; outputs chunks that are few hundreds bytes each as a result of
; compression. If you prefer a larger chunk size for better
; performance, enable output_buffering in addition.
; Note: You need to use zlib.output_handler instead of the standard
; output_handler, or otherwise the output will be corrupted.
; Ссылка
zlib.output_compression = Off