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I have a set of files that are commonly used as inputs in my tex files, so I put them in a directory and set the path in the TEXINPUTS environment variable (in Ubuntu). This works fine when compiling files with the latex command, but if I compile them with pdftex, it gives the following error message:

! I can't find file `{header.tex}'.
l.1 \input{header.tex}

As far as I can tell, pdftex is completely ignoring the TEXINPUTS environment variable. Does it use a different environment variable? How can I get it to recognise a path?

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Are you using pdftex or pdflatex. The latter will read \input{header.tex} as a braced argument for file header.tex, but pdftex is Knuth's plain format with the pdfTeX engine: there, \input has primitive syntax only, and the file name searched is {input.tex}. –  Joseph Wright Nov 18 '12 at 12:38
Aha! pdflatex works, but pdftex doesn't. Thanks for explaining. –  thornate Nov 18 '12 at 12:52
I'll write that up in a slightly modified form as an answer, then :-) –  Joseph Wright Nov 18 '12 at 13:06
Start your documents with \NeedsTeXFormat{LaTeX2e} to get a meaningful error message if you use the wrong program. –  Martin Schröder Nov 19 '12 at 7:41
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up vote 6 down vote accepted

The latex command runs LaTeX in DVI-output mode. LaTeX's definition of \input allows for a syntax


where the <file-name> is read as a braced argument. The pdflatex command will do exactly the same but with direct PDF output.

On the other hand, pdftex runs plain TeX with direct PDF output. The plain TeX definition for \input uses a 'primitive' syntax, in which the name is read as any tokens at all up to the first space. Thus with pdftex


ends up looking for a file called {<file-name>}, including the braces.

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It may be worth noting that \input{filename} works also in LuaTeX (as opposed to LuaLaTeX). –  egreg Nov 18 '12 at 13:46
@egreg One of the 'features' of LuaTeX which gives me headaches :-) –  Joseph Wright Nov 18 '12 at 14:00
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