Why does wkhtmltopdf work via Terminal and fail via PHP's shell_exec() when using MAMP?

Question: Why does the following command line command:

wkhtmltopdf /path/to/html/input/file.html /path/to/pdf/output/file.pdf

work as expected when executed via Mac OSX Terminal but fail when executed via PHP's shell_exec() function via MAMP?

Answer: You need to comment out two lines of code within one of MAMP's configuration files.

Within MAMP's /Applications/MAMP/Library/bin/envvars file you'll notice the following two lines:

DYLD_LIBRARY_PATH="/Applications/MAMP/Library/lib:$DYLD_LIBRARY_PATH"
export DYLD_LIBRARY_PATH

Comment both of them out as demonstrated below (note the "#" prefix on each line):

#DYLD_LIBRARY_PATH="/Applications/MAMP/Library/lib:$DYLD_LIBRARY_PATH"
#export DYLD_LIBRARY_PATH

Lastly, within the same file, add the following command to make sure the $PATH environment variable inherited by PHP from Apache includes the directory that contains your wkhtmltopdf executable. Your command will look something like:

export PATH=/parent/path/of/wkhtmltopdf/executable:$PATH

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