如何使Shell命令与exec在php中一起工作

Question

When I run in a terminal:

convert file.pdf file.png

everything works fine, but when I do this in a php script as:

exec('convert file.pdf file.png');

I get errors. When I search online how to solve these errors I end up making subtle changes to files here, and permissions there. The errors change and I have no idea how I got to where I am. I feel as though I am chasing a phantom.

I don't know whether the problem lies with imagemagick, php, ghostscript, permissions, etc.

So my question is: How should I go about so that I can re-attack this problem from the beginning? Do I need to reinstall things? If so, what and on what order? What should have what permissions?

I appreciate that my question is rather open, but judging by the multitude of similar questions, with all sorts of different answers, it would be good to have some clear definite checklist to work through.

For completeness I am using mac osx, Yosemite; php 5.5.27; ImageMagick 6.9.1-10; gs 9.16 and the present error says:

convert: no images defined `file.png' @ error/convert.c/ConvertImageCommand/3230.

I am also using full path names for the convert and the files too.

With 'shell_exec' I get more error messages:

dyld: Library not loaded: /usr/local/lib/libtiff.5.dylib 
Referenced from: /usr/local/bin/gs  
Reason: Incompatible library version: gs requires version 8.0.0 or later, but libtiff.5.dylib provides version 6.0.0

convert: FailedToExecuteCommand `"gs" -q -dQUIET -dSAFER -dBATCH -dNOPAUSE - dNOPROMPT -dMaxBitmap=500000000 -dAlignToPixels=0 -dGridFitTT=2 "-sDEVICE=pngalpha" -dTextAlphaBits=4 -dGraphicsAlphaBits=4 "-r300x300"  "-sOutputFile=/var/tmp/magick-9254642RiQMO2CuWM%d" "-f/var/tmp/magick-92546j8PosqIIrra3" "-f/var/tmp/magick-92546LB13giWos7rr"' (-1) @ error/delegate.c/ExternalDelegateCommand/483.

convert: no images defined `file.png' @ error/convert.c/ConvertImageCommand/3230.

Answer 1

请注意，PHP的shell_exec带有字符串参数：

shell_exec('convert file.pdf file.png');