How to read Java properties files using bash or shell.

Method 1 - Scan through the file to get an individual property

This works well if you just want to read a specific property in a Java-style properties file. Here's what it does:

1. Remove comments (lines that start with '#')
2. Grep for the property
3. Get the last value using tail -n 1
4. Strip off the property name and the '=' (using {{cut -d "=" -f2-}) to handle values with '=' in them, as a commenter suggested).

It can also be handy to strip off the leading and trailing blanks with this sed expression:

Which makes the whole thing look like this:

Shell scripts can use this technique to set environment variables, for example:

Method 2 - Convert the properties file to a shell script, then run it

This method is good for when you want to read the whole properties file. However, it only works if the property names are valid shell variable names. For example, property names with a '.' in them will cause this to break. Here is the original article that inspired this method.

Security Note These techniques generate shell code from the properties file, then execute the generated code. This can be a potential security issue if the properties file has hidden shell code in it. Make sure you have appropriate access control on the properties file in this case.

The steps are:

1. Create a temp file.
2. Stream the properties file, convert it to unix LF format (unless you are sure the file was produced on Linux).
3. (not sure what the first 'sed' does)
4. Double quote all the values, to preserve spaces.
5. Source in the file. Shell should ignore Java properties file comments automatically.
6. Erase the temp file.

Here is the code:

Method 2 reloaded - Use AWK

This method is the same as the previous one except we use an inline awk script to replace any non-alpha-digit-underscore characters in the property names with underscore. This solves the problem the previous method has when it processes properties that have '.' in the name, for example.

Some clever person could probably figure out how to do the same thing with sed, but awk works.

Steps:

1. Create a temporary file.
2. Stream the properties file to stdout and (optionally) filter out dos style linefeeds.
3. Split each line using "=" as the field separator. If there are exactly two fields, then substitute the non-identifier characters with underscore in the first one, and print the second field with quotes around it.
4. If the line doesn't have an =, or seems to have more than two values, just print it out.
5. Source in the temporary file and delete it.

Method 2 - Using Groovy

Use this if you have to really read properties files with interpolation!

If you have Groovy installed already you can use it to read ANT-style properties files (complete with interpolation), and generate a shell file that will set all the environment variables:

This reads the properties file (the first argument) and optionally the default properties file (the second argument), and writes the shell statements to stdout. Since we're using ANT to read in the properties files, this version has a lot more functionality:

• All the standard ANT properties will be processed.
• ANT will interpolate the property values.

So, if we have the following properties file:

The generated shell script will contain:

Edge Case - Shell commands in property values

What happens when the properties file looks like this?

When we use the Groovy script with this file, we hit an edge case:

Uh oh! This property value could have done something very bad. We can change the Groovy script to escape any single quotes like this:

However, this may break some things. Of course, this isn't a problem if you don't embed shell commands into your properties files... with single quotes around them.

See Also

• The '.properties' file format
• Remove comments using sed
• http://www.mslinn.com/blog/index.php/archives/2004/11/03/reading-java-properties-files-from-bash
• Here is a solution that works in some special cases, but not in general: http://www.coderanch.com/t/419731/Linux-UNIX/read-properties-file-through-script#2347487
• StackExchange question - http://stackoverflow.com/questions/1682442/reading-java-properties-file-from-bash