Writing variables to file with bash

Question

I'm trying to configure a file with a bash script. And the variables in the bash script are not written in file as it is written in script.

Ex:

#!/bin/bash

printf "%s" "template("$DATE\t$HOST\t$PRIORITY\t$MSG\n")" >> /file.txt

exit 0

This results to template('tttn') instead of template("$DATE\t$HOST\t$PRIORITY\t$MSG\n in file.

How do I write in the script so that the result is template("$DATE\t$HOST\t$PRIORITY\t$MSG\n in the configured file?

Is it possible to write variable as it looks in script to file?

Didier Trosset · Accepted Answer · 2016-02-11 07:23:11Z

3

Enclose the strings you want to write within single quotes to avoid variable replacement.

> FOO=bar
> echo "$FOO"
bar
> echo '$FOO'
$FOO
>

answered Feb 11, 2016 at 7:23

Didier Trosset

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1 Comment

Glen K Over a year ago

Since the question is, "Writing variables to file in bash", it would be helpful (to those who end up here when searching for "write variable to file") if your example included writing the variable's value to a file.

hgiesel · Accepted Answer · 2016-02-11 07:25:53Z

2

Using printf in any shell script is uncommon, just use echo with the -e option. It allows you to use ANSI C metacharacters, like \t or \n. The \n at the end however isn't necessary, as echo will add one itself.

echo -e "template(${DATE}\t${HOST}\t${PRIORITY}\t${MSG})" >> file.txt

The problem with what you've written is, that ANSI C metacharacters, like \t can only be used in the first parameter to printf.

So it would have to be something like:

printf 'template(%s\t%s\t%s\t%s)\n' ${DATE} ${HOST} ${PRIORITY} ${MSG} >> file.txt

But I hope we both agree, that this is very hard on the eyes.

answered Feb 11, 2016 at 7:25

hgiesel

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Comments

heinrichmartin · Accepted Answer · 2022-11-02 12:24:27Z

1

There are several escaping issues and the power of printf has not been used, try

printf 'template(%s\t%s\t%s\t%s)\n' "${DATE}" "${HOST}" "${PRIORITY}" "${MSG}" >> file.txt

Reasons for this separate answer:

The accepted answer does not fit the title of the question (see comment).
The post with the right answer
- contains wrong claims about echo vs printf as of this post and
- is not robust against whitespace in the values.
The edit queue is full at the moment.

answered Nov 2, 2022 at 12:24

heinrichmartin

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