CODEWITHSUNDEEP
bashunixfile-io
Kim Stacks
Kim Stacks

Reputation: 10812

bash script to write content into file. File content requires bash variables. How to do that?

The following is a piece of content my bash script will write into the nginx configuration file.

WEBAPP=example.com
APPFOLDER=abcapp
CONFFILENAME=abc.conf

read -r -d '' FILECONTENT <<'ENDFILECONTENT'
server {
        listen 80;
        client_max_body_size 2M;
        server_name $WEBAPP;
        root /var/virtual/stage.$WEBAPP/current/src/$APPFOLDER/webroot;
}

ENDFILECONTENT
echo "$FILECONTENT" > /etc/nginx/sites-available/$CONFFILENAME

The code works successfully to write the content inside /etc/nginx/sites-available/abc.conf.

However, I have two bash variables in $WEBAPP and $APPFOLDER. They are manifested exactly like that inside the file instead of example.com and abcapp which is what I intended.

How do I make the script work as intended?

Upvotes: 1

Views: 5057

Answers (2)

rici
rici

Reputation: 241721

bash allows newlines in quoted strings. It does parameter replacement (that is, $FOO gets replaced with the value of FOO) inside double-quoted strings ("$FOO") but not inside single-quoted strings ('$FOO').

So you could just do this:

FILECONTENT="server {
        listen 80;
        client_max_body_size 2M;
        server_name $WEBAPP;
        root /var/virtual/stage.$WEBAPP/current/src/$APPFOLDER/webroot;
}"
echo "$FILECONTENT" > /etc/nginx/sites-available/$CONFFILENAME

You don't really need the FILECONTENT parameter, since you could just copy directly to the file:

cat >/etc/nginx/sites-available/$CONFFILENAME <<ENDOFCONTENT
server {
        listen 80;
        client_max_body_size 2M;
        server_name $WEBAPP;
        root /var/virtual/stage.$WEBAPP/current/src/$APPFOLDER/webroot;
}
ENDOFCONTENT

In the second example, using <<ENDOFCONTENT indicates that the $VARs should be replaced with their values <<'ENDOFCONTENT' would prevent the parameter replacement.

Upvotes: 5

Jeff Bowman
Jeff Bowman

Reputation: 95634

You're actually deliberately turning off parameter subsitution by enclosing 'ENDFILECONTENT' in quotes. See this excerpt from example 19-7 of the advanced Bash scripting guide on Heredocs, slightly reformatted:

# No parameter substitution when the "limit string" is quoted or escaped.
# Either of the following at the head of the here document would have
# the same effect.
#
# cat <<"Endofmessage"
# cat <<\Endofmessage

Remove the single quotes around 'ENDFILECONTENT' and BASH will replace the variables as expected.

Upvotes: 1

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