The a2ps utility is for formatting files for printing on a PostScript printer, hence its name is not a2pdf.
The file you created under Linux (or OS X), which is a miss-named .pdf file, is in fact a PostScript file and many Linux Distros will open it anyway. Thus leading you to believe is was a PDF Document when in reality it's not.
Looking at the file created under Linux in a Hex Editor its header starts off with, e.g., %!PS-Adobe-3.0 and a PDF Document starts with, e.g., %PDF-1.6%.
This is why you get the "The file “filename.pdf” could not be opened. It may be damaged or use a file format that Preview doesn’t recognize." error message under OS X when trying to open a PostScript Document with a miss-named PDF Document extension.
Update: Installing a2pdf
After doing a little research I found a2pdf. Further research required having Font::TTF::Font and PDF::API2 also installed. So I downloaded all three packages master.zip (for a2pdf), Font-TTF-1.04.tar.gz and PDF-API2-2.023.tar.gz.
Next I extracted all three and installed them in the same manner in the following order, Font::TTF::Font, PDF::API2 then the master.zip (for a2pdf). I did this in a Terminal using the following commands.
$ cd $target_directory
$ perl Makefile.PL
$ make
$ sudo make install
I then tested, from my Home Directory, with: a2pdf filename.txt > filename.pdf
It create filename.pdf and I then opened it in Preview just fine as a PDF Document.
That said, there are other modules that can be installed to do things like syntax highlighting, e.g. Perl::Tidy. So you'll need to do a bit more research to utilize the full capabilities of a2pdf.
Note: I have Xcode and Command Line Tools for Xcode installed and as long as you have Command Line Tools for Xcode installed, which is a Homebrew prerequisite, you can install all of this from the Terminal the old fashioned way if not available from Homebrew, which I do not believe it is.
Sounds as if you may have run your system out of RAM, which is quite possible with the anemic Air designs Apple is passing off as computers these days.
you may well need to do a hard shut-down and reboot.. hold down power button till it shuts off, then wait 5-10 seconds and reboot.
If terminal does the same thing after that, then you may have an actual issue..
Best Answer
Usually, installation instructions recommend a restart of Terminal if the installation modified some shell startup files (some probably recommend it even it would not be strictly necessary).
Alternative approaches:
. ~/.zshrc) the startup files manually,exec zsh -lto replace the current shell with a newly initialized version (replacezshwith the shell you are actually using),