rudi's posterous

Editing LaTeX on your iPad, with some help from Hazel

Wed, 04 Apr 2012 06:06:00 -0700

There is no (La)TeX implementation that runs on the iPad, so it's a bit difficult to edit Latex documents there. I hacked together a solution involving Dropbox, Hazel and Textastic. Textastic is not strictly necessary, but it is a nice editor that features Dropbox integration, syntax highlighting for Latex, and pdf previewing (although it will not pick up changes in the pdf file automatically at the moment). Update: Alexander Blach, the author of Textastic, told me to use Remote Live Preview and navigate to the pdf from the dropbox website. Once you see your pdf, hit Return on the URL one more time so that Textastic remembers it. A little fiddly, but works great once the URL is set.

With this recipe, Latex files can be edited on the iPad and will be converted by a stationary Mac into pdf when they are updated on Dropbox. The pdf can then be viewed from the Dropbox app, or directly from within your editor if it supports pdf viewing.

First, you create a directory, for example ~/Dropbox/LaTeX and tell Hazel to watch for changes in that directory:

Then, set up a rule "Compile latex file" to work with changed .tex files that fulfill certain conditions:

Now, insert the first script which checks whether the rule should fire. The pdf should be regenerated whenever the tex file is newer (and also newer than the log file, which will stay around if there was a compilation error previously).

Click on "Edit script" on the "Passes shell script" line, set the shell to /bin/bash in the first line of the dialog box and paste the following into the text area:

PDFFILE=$(basename "$1" .tex).pdf
LOGFILE=$(basename "$1" .tex).log
if [ "$1" -nt "$PDFFILE" -a "$1" -nt "$LOGFILE" ]
then
  exit 0
fi
exit 1

In the same way, insert this script, which runs Latex (and bibtex if necessary, although I have not tested this part) into the dialog popup box on the "Run shell script" line:

set -e
TEXFILE=$1
BASENAME=$(basename "$TEXFILE" .tex)
PDFFILE="$BASENAME.pdf"
pdflatex "$TEXFILE"
if [ "$BASENAME.blg" -nt "$TEXFILE" ]
then
  bibtex "$BASENAME"
  pdflatex "$TEXFILE"
fi
pdflatex "$TEXFILE"
if [ -f "$PDFFILE" ]
then
  rm -f "$BASENAME.aux" "$BASENAME.log" "$BASENAME.toc" "$BASENAME.bbl" "$BASENAME.blg" "$BASENAME.lof" "$BASENAME.idx"
fi

The way this works is that Hazel checks on every change to the tex file whether it is newer than its pdf file, and if yes, re-generates the pdf file and removes any intermediate files. In case there is an error in the file, the script will abort (because of the "set -e" on the first line), and Hazel will not attempt to run it again (since the log file will stick around) before the tex file is changed again.

Now, as long as my office computer is running, I can edit Latex files on the go, hit "upload" from within Textastic, wait a second or two, switch to Live Preview and see my changes in PDF form. Nice!

rudi's posterous

Editing LaTeX on your iPad, with some help from Hazel

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