\read (LaTeX2e unofficial reference manual (November 2018))

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### 27.2 `\read`

Synopsis:

    \readnumber tomacro

Make the command macro contain the next line of input from text stream number, as in `\read5 to\data`.

This opens the file `email.tex` for reading, puts the contents of the first line into the command `\email`, and then closes the file.

    \newread\recipientfile
    \openin\recipientfile=email
    \read\file to\email
    \typeout{Email address: \email}
    \closein\recipientfile

If number is outside the range from 0 to 15 or if no file of that number is open, or if the file has ended, then `\read` will take input from the terminal. Note, though, that the natural way in LaTeX to take input from the terminal is `\typein` (see \typein).

To read in an entire file at once use `\input` (see \input) or `\include` (see \include & \includeonly).

A common reason to want to read from a data file is to do mail merge. CTAN has a number of packages for that; one is `datatool`.

Unofficial LaTeX2e reference manual