Write content into a file with bash script

Question

I'm trying to create a bash script in order to daemonized celeryd task. In my bash script, I need to create some files and add content. This content have a variable given by user named $app_name with read method and some others variables in the content.

Issue:

When I copy the content located in my bash script to the given path, it doesn't copy variables already present inside.

Example:

In my bash script I have :

########################
# Get application name #
########################

read -p "Define the application name (lowercase and without spaces): " app_name
echo "You defined the application name: $app_name"

############################################################
# Create service file /usr/local/etc/rc.d/celeryd_app_name #
############################################################

cat > /usr/local/etc/rc.d/celeryd_$app_name << EOF
#!/bin/sh
# =====================================================
#  celeryd_$app_name - Starts the Celery worker daemon.
# =====================================================
#
# :Usage: /etc/init.d/celeryd_$app_name {start|stop|force-reload|restart|try-restart|status}
# :Configuration file: /etc/default/celeryd_$app_name

### BEGIN INIT INFO
# Provides:          celeryd_$app_name
# Required-Start:    $network $local_fs $remote_fs
# Required-Stop:     $network $local_fs $remote_fs
# Default-Start:     2 3 4 5
# Default-Stop:      0 1 6
### END INIT INFO
EOF

But if I open the created file I get:

### BEGIN INIT INFO
# Provides:          celeryd_$app_name
# Required-Start:    
# Required-Stop:     
# Default-Start:     2 3 4 5
# Default-Stop:      0 1 6
### END INIT INFO

It doesn't copy $network $local_fs $remote_fs which are present in the content.

There is another way to do that ?

Thank you !

In FreeBSD bash is not installed by default, I would suggest using pure sh so you could make your script more portable. — nbari
– nbari, Commented Mar 18, 2019 at 9:24
Check this answer stackoverflow.com/a/42666651/1135424 basically I mean to use only sh POSIX-compliant — nbari
– nbari, Commented Mar 18, 2019 at 9:29
@nbari I read the answer. Ok but I don't understand why my bash script won't be pure sh. Furthermore I execute my script trough sh celeryd.sh. All things work fine, except the copy into files, it doesn't copy variables if they are not defined in my bash script. — Essex
– Essex, Commented Mar 18, 2019 at 9:35
You may want to investigate the difference between cat << EOF and cat << \EOF. — AlexP
– AlexP, Commented Mar 18, 2019 at 9:43

nbari · Accepted Answer · 2019-03-18 10:34:51Z

What is happening is that the here document is expanding the variables and since they are not declared you are getting empty values, from the wiki:

By default, behavior is largely identical to the contents of double quotes: variable names are replaced by their values, commands within backticks are evaluated, etc

$ cat << EOF
> \$ Working dir "$PWD" `pwd`
> EOF
$ Working dir "/home/user" /home/user

This can be disabled by quoting any part of the label, which is then ended by the unquoted value; the behavior is essentially identical to that if the contents were enclosed in single quotes. Thus for example by setting it in single quotes:

$ cat << 'EOF'
> \$ Working dir "$PWD" `pwd`
> EOF
\$ Working dir "$PWD" `pwd`

So from your example, you could modify your script to be something like:

#!/bin/sh

cat << 'EOF' > /usr/local/etc/rc.d/celeryd_$app_name
#!/bin/sh
# =====================================================
#  celeryd_$app_name - Starts the Celery worker daemon.
# =====================================================
#
# :Usage: /etc/init.d/celeryd_$app_name {start|stop|force-reload|restart|try-restart|status}
# :Configuration file: /etc/default/celeryd_$app_name
### BEGIN INIT INFO
# Provides:          celeryd_$app_name
# Required-Start:    $network $local_fs $remote_fs
# Required-Stop:     $network $local_fs $remote_fs
# Default-Start:     2 3 4 5
# Default-Stop:      0 1 6
### END INIT INFO
EOF

Which then will produce the output:

#!/bin/sh
# =====================================================
#  celeryd_$app_name - Starts the Celery worker daemon.
# =====================================================
#
# :Usage: /etc/init.d/celeryd_$app_name {start|stop|force-reload|restart|try-restart|status}
# :Configuration file: /etc/default/celeryd_$app_name
### BEGIN INIT INFO
# Provides:          celeryd_$app_name
# Required-Start:    $network $local_fs $remote_fs
# Required-Stop:     $network $local_fs $remote_fs
# Default-Start:     2 3 4 5
# Default-Stop:      0 1 6
### END INIT INFO

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