Can (La)TeX compare the time stamps of two external files?

Question

Scenario

I have a bunch of standalone PSTricks files. Each of those files can be compiled by latex-dvips-ps2pdf-pdfcrop-pdftops to produce a PDF image. I have made a batch file to do latex-dvips-ps2pdf-pdfcrop-pdftops.

In my main input file, I will iterate through the PSTricks files. For each iteration, I check whether or not the corresponding PDF exists. If the corresponding PDF already exists, I check whether or not its time stamp is newer than that of its .tex file. Otherwise I will invoke \immediate\write18 mybatch.bat filename.tex to produce or re-produce the corresponding PDF file.

Question

Can (La)TeX compare the time stamps of two external files? Providing the complete working source code for my scenario above is preferred. :-)

Note: Actually I can make an external script to iterate through the PSTricks files and invoke this script only once from within the main input file. But I am interested in creating the hybrid solution.

Answer 1

I wrote the filemod package just for this task which I also need for the upcoming version of standalone. It requires pdf(La)TeX or Lua(La)TeX but doesn't work with Xe(La)TeX.

Basic Usage:

\Filemodcmp{<file 1>}{<file 2>}{<1 is newer>}{<2 is newer>}

There is also a fully expandable version called \filemodcmp and also macros to find the newest or oldest file from a given list.

Answer 2

\def\comparetimestamp#1#2{%
  \ifnum\pdfstrcmp{\pdffilemoddate{#1}}{\pdffilemoddate{#2}}<0
    \message{#1 is older than #2}%
  \fi}

Change the \message line to what you need. Not usable with XeLaTeX, only with (pdf)latex. It may give problems if there's a change in the time zone (for example when changing to or from DST) between runs, but this should not be a problem.

Answer 3

You could use luatex. ConTeXt wrapper mtxrun provides one such implementation based on timestamps

mtxrun --iftouched=file.tex,file.pdf --direct pdflatex file 

and one based on md5 sum

mtxrun --ifchanged=file.tex --direct pdflatex file

which creates a md5 sum for file.tex and run the command only if the md5 sum has changed. See the source code of mtxrun.lua for implementation. The relevant functions are:

function file.needs_updating(oldname,newname,threshold) -- size modification access change
    local oldtime = lfs.attributes(oldname, modification)
    local newtime = lfs.attributes(newname, modification)
    if newtime >= oldtime then
        return false
    elseif oldtime - newtime < (threshold or 1) then
        return false
    else
        return true
    end
end

function file.checksum(name)
    if md5 then
        local data = io.loaddata(name)
        if data then
            return md5.HEX(data)
        end
    end
    return nil
end

function file.loadchecksum(name)
    if md5 then
        local data = io.loaddata(name .. ".md5")
        return data and (gsub(data,"%s",""))
    end
    return nil
end

Rest is just a matter of wrapping them around user macros.

Answer 4

This answer will have nothing to do with TeX, but I would like to point out that using the right tools greatly simplifies the solution. In this case, you should use make. There is a good manual on this tool here.

A very simple Makefile follows (it should be expanded further to fit good practices):

TARGETS = <list of targets to build> (GNU Make's wildcard and patsubst might help)

.PHONY: all clean

all: $(TARGETS)

%.pdf: %.tex
    <call your batch file or directly integrate commands here, $< stands for source name>

clean:
    $(RM) $(TARGETS)

Now just type make at any time and it will ensure the targets are up to date.