mjhjmtu

I have a properties file that looks like this:

mysql.username=USERNAME
mysql.pass=PASS

I need to change USERNAME and PASS with variable values passed to shell script. I cannot use sed since that will work fine the first time to replace USERNAME and PASS with "values" but once they are replaced, sed will not find the variable names in the file the second time the script runs and thus an issue.

How can this be handled?

You can obtain old parameters from the properties file before using sed, e.g.

# get old parameters
$ export oldUsername=$(grep mysql.username $FILE | cut -d'=' -f2)
$ export oldPass=$(grep mysql.pass $FILE | cut -d'=' -f2)

# set new parameters
$ export newUsername=NEW_USERNAME
$ export newPass=NEW_PASS

# change parameters
$ sed -i "s/$oldUsername/$newUsername/g" $FILE
$ sed -i "s/$oldPass/$newPass/g" $FILE

You can use below.

[user@xyz ~]$ hh='mysql.username=USERNAME';echo $hh | awk -F"=" 'OFS=FS $2="Mango"; print '
mysql.username=Mango

You should regenerate this file from a template using your configuration management system of choice.

You could also write a shell script that uses a heredoc to do the same thing. But since we're in DevOps-land you really should be using your configuration management system for these things.

Maybe, this is something you can try - in sed they are known as back-references:

$1 - is the value passed for username

$2 - is the value passed for password

1 captures the back reference within ( and )

sed -i "s/(mysql.username=).*/1$1" propertiesfile
sed -i "s/(mysql.pass=).*/1$2" propertiesfile