The default commands for pdftex and pdflatex are now "pdftex --shell-escape" and "pdflatex --shell-escape." The "shell-escape" portion of this text tells pdftex that it is legal to run other programs during typesetting. This is useful because if tex finds a graphic file in an unsupported format, it can automatically call another program to convert it to supported format. For example, the default Latex template automatically converts tif files to png and automatically converts eps files to pdf.

This creates one difficulty that may worry some users. The "shell-escape" flag allows pdftex to run ANY program. Thus a disgruntled student could send you a tex source file by email and when you typeset it you would discover that some of the files in your directory had been erased.

I believe the danger is slight. A source file which did harm would have to be created deliberately, but sending a "virus" via tex source seems somewhat esoteric. Nevertheless, there are two ways that you can protect yourself. The first and easiest is to remove the letters "--shell-escape" from the two spots they occur in Preferences and then convert all of your graphic files by hand.

TeXShop now provides a different protection. A preference item under the Engine tab is labeled "Shell Escape Warning." This item is off when TeXShop is delivered. If the item is on and "shell-escape" is active, then the first time a file is typeset during a TexShop session, a warning dialog will appear allowing you to turn shell-escape off for that particular file. This dialog will not appear again during the session for that particular file. Thus you can typeset your own files using "shell-escape" and typeset files received in the mail without "shell-escape."

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Shell Escape Protection