Is there an elegant way to set a shell variable to the contents of a file?

Question

Say I have some configuration data in a file config. For convenience, I'd like to load this data into a shell variable, CONFIG_DATA.

Obviously I can do:

CONFIG_DATA="$(cat config)"

But this kinda feels like a useless use of cat to me. Is this the only way to do this? Or is there a more elegant way to do it?

Answers should prefer POSIX but may use any shell.

Reading an entire file in memory like this is almost always a bad idea, regardless of how you write it. — Satō Katsura
– Satō Katsura, Commented Dec 13, 2016 at 6:36
@SatoKatsura in some cases very true. however for the purpose of this question, you may assume that the file is super tiny, so it's not a major problem. — strugee
– strugee, Commented Dec 13, 2016 at 6:42

JdeBP · Accepted Answer · 2016-12-13 09:26:28Z

23

In Bash and the Z shell, at least, there is a faster way:

CONFIG_DATA=$(<config)

To quote from the Bourne Again shell's man page:

The command substitution $(cat file) can be replaced by the equivalent but faster $(< file).

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answered Dec 13, 2016 at 2:57

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