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best way to write a dynamic conf file in bash

Hi there. I tend to write a lot of shell scripts to do installations and configurations of varios Linux software. Now because I want to dynamically write config files for systems (say for example postfix, etc), I am trying to figure out the most effective way to accomplish this. Does anyone have any suggestions? I would hate to have to write out echo statements. I would like to maybe have a "template" file in which the script would make a copy and substitute variables in the final output config file.

I was thinking of something like:

Code:

#!/bin/bash

# a var used in the template config file

declare -rx MYDB="postfix"

# a template config file

declare -rx TEMPATECFG="my.template.conf"

# The final config file with proper substitutions

declare -rx TMPFILE="my.conf"

# read in the template

while read curline; do

    echo "$curline" >> $TMPFILE

done < my.temnplate.conf

Then in my template file I would have something like:

Code:

grant SELECT ON $MYDB.* to 'postfix'@'localhost' IDENTIFIED by 'somePass';

The actual code in the template file is really irrelevant to this question, and I was just providing an example.

Now obviously the above code does not work as the variable substitution does not happen.

So I guess I am just hoping to get a pointer on how others may have done this kind of thing.

Ultimately I just want to write dynamic config files.

Thanks!

Have you looked m4 for these activities?

Cheers,
Tink

Sorry - I do not understand your question... m4?

Search google for m4, its a language that might be better suited to the task you want.

And to give some more input: m4 is a macro processor; it's been
designed for this kind of task where you can have "variables" in
files and get those replaced. It's somewhere between sed and perl :}

Cheers,
Tink

Does the technique in the example you gave work?

I can think of 2 other purely bash ways to populate .conf template w/ custom entries.

1st -- Use sed -i to do the replacements in the copy of the template. (Or awk.)

2nd -- Write the template(s) as series of functions that are called by the script after the template is sourced. I believe -- I didn't test this -- that the functions which are sourced would inherit the variables of the "parent" script.

If it's just that you hate, as I do, multiple echo statements, what about here docs?
--> man bash "Here Documents".

Quote:

Originally Posted by archtoad6

Does the technique in the example you gave work?

If it's just that you hate, as I do, multiple echo statements, what about here docs?
--> man bash "Here Documents".

No the technique I used does not work.... I really did not expect it to, I was however just trying to show what I was trying to accomplish.

I had thought of the here documents thing and tried it, but it was a misunderstanding on my part that caused me to abbanodon it, however I figured it out just now what I was doing wrong...

This works for my purposes:

Code:

#!/bin/bash

touch myconf.conf

cat > myconf.conf << POST_CONF

param1 = $1

param2 = $2

param3 = $3

POST_CONF

cat myconf.conf

rm myconf.conf



exit 0

What I had done wrong was a misunderstanding between redirection and the use of "<<" with a here doc. So when I was trying that in the first place - it was giving me issues!