Re: \inputif(file)exist(s)

[Aditya Mahajan <adityam@umich.edu>]

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On Thu, 3 May 2012, Procházka Lukáš Ing. - Pontex s. r. o. wrote:

> Hello,
>
> just a quick question - is there a command like "\inputif(file)exist(s)", 
> which will \input a file if it exists, i.e. with no error if it doesn't?

\readfile.

From file-res.mkvi

%D \macros
%D   {readfile,ReadFile}
%D
%D One cannot be sure if a file exists. When no file can be
%D found, the \type{\input} primitive gives an error message
%D and switches to interactive mode. The macro \type{\readfile}
%D takes care of non||existing files. This macro has two faces.
%D
%D \starttyping
%D \ReadFile {filename}
%D \readfile {filename} {before loading} {not found}
%D \stoptyping
%D
%D Many \TEX\ implementations have laid out some strategy for
%D locating files. This can lead to unexpected results,
%D especially when one loads files that are not found in the
%D current directory. Let's give an example of this. In
%D \CONTEXT\ illustrations can be defined in an external file.
%D The resizing macro first looks if an illustration is defined
%D in the local definitions file. When no such file is found,
%D it searches for a global file and when this file is not
%D found either, the illustration itself is scanned for
%D dimensions. One can imagine what happens if an adapted,
%D localy stored illustration, is scaled according to
%D dimensions stored somewhere else.
%D
%D When some \TEX\ implementation starts looking for a file, it
%D normally first looks in the current directory. When no file
%D is found, \TEX\ starts searching on the path where format
%D and|/|or style files are stored. Depending on the implementation
%D this can considerably slow down processing speed.
%D
%D In \CONTEXT, we support a project||wise ordening of files.
%D In such an approach it seems feasible to store common files
%D in a lower directory. When for instance searching for a
%D general layout file, we therefore have to backtrack.
%D
%D These three considerations have lead to a more advanced
%D approach for loading files.
%D
%D We first present an earlier implementation of
%D \type{\readfile}. This command backtracks parent
%D directories, upto a predefined level. Users can change this
%D level (on the commandline using a directive); we default to~3.
%D
%D We use \type{\normalinput} instead of \type{\input}
%D because we want to be able to redefine the original
%D \type{\input} when needed, for instance when loading third
%D party libraries.


Aditya

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