Bash: Reuse printf variables in output

Question

Is it possible to use the variables passed to printf more than once in the formatting?

For example, with this line:

printf 'Hi %s, welcome to %s. %s is a great place to work. Thanks %s.' "John" "The Icecream Factory"

How can I "reuse" the first and second variables in printf?

I'm thinking something like:

printf 'Hi %s[1], welcome to %s[2]. %s[1] is a great place to work. Thanks %s[2].' "John" "The Icecream Factory"

... but obviously that's not it.

Desired output

Hi John, welcome to The Icecream Factory. The Icecream Factory is a great place to work. Thanks John.

Actual output

Hi John, welcome to The Icecream Factory.  is a great place to work. Thanks .

Working environment is bash in Ubuntu 20.

I don't believe printf format characters support that. What's the reason you have to use %s? It's easier to define variables, which can be used multiple times in a String, e.g. n="John"; f="The Icecream Factory"; printf "Hi $n, welcome to $f. $f is a great place to work. Thanks $n." — Taylor G.
– Taylor G., Commented Apr 25, 2021 at 4:08
Yes, that works fine, but I've been told it's bad practice to use variables in the printf format string: github.com/koalaman/shellcheck/wiki/SC2059 — algalg
– algalg, Commented Apr 25, 2021 at 5:44
There are pitfalls to be aware of but it's not that serious. You can also use echo instead — CervEd
– CervEd, Commented Jun 8, 2023 at 6:19

Shawn · Accepted Answer · 2021-04-25 05:34:53Z

2

While I don't think it's possible using either the built-in bash implementation of printf or the freestanding GNU printf(1) program, if you can target zsh instead, its version of printf supports POSIX-style printf(3) argument indexing:

Normally, conversion specifications are applied to each argument in order but they can explicitly specify the nth argument is to be used by replacing % by %n$ and * by *n$. It is recommended that you do not mix references of this explicit style with the normal style and the handling of such mixed styles may be subject to future change.

$ printf 'Hi %1$s, welcome to %2$s. %2$s is a great place to work. Thanks %1$s.\n' "John" "The Icecream Factory"
Hi John, welcome to The Icecream Factory. The Icecream Factory is a great place to work. Thanks John.

edited Apr 25, 2021 at 5:34

answered Apr 25, 2021 at 5:26

Shawn

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1 Comment

Shawn Over a year ago

If this is ever added to bash, it would almost certainly use the same syntax, fwiw.

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