Apache Ant provides an optional task for editing property files. This is very useful when wanting to make unattended modifications to configuration files for application servers and applications. Currently, the task maintains a working property file with the ability to add properties or make changes to existing ones. Since Ant 1.8.0 comments and layout of the original properties file are preserved.

Since Ant 1.8.2 the linefeed-style of the original file will be preserved as well, as long as style used to be consistent. In general, linefeeds of the updated file will be the same as the first linefeed found when reading it.

PropertyFile Task


Attribute Description Required
file Location of the property file to be edited Yes
comment Header for the file itself No
jdkproperties Use java.lang.Properties, which will lose comments and layout of file. since Ant 1.8.0 No; default is false

The boolean attribute jdkproperties is provided to recover the previous behaviour of the task, in which the layout and any comments in the properties file were lost by the task.

Parameters specified as nested elements


Use nested <entry> elements to specify actual modifications to the property file itself.

Attribute Description Required
key Name of the property name/value pair Yes
value Value to set (=), to add (+) or subtract (-) At least one must be specified, if operation is not del
default Initial value to set for a property if it is not already defined in the property file.
For type date, an additional keyword is allowed: now
type Regard the value as: int, date or string (default) No; defaults to string
operation One of the following operations:
for all datatypes:
  • del : deletes an entry
  • + : adds a value to the existing value
  • = : sets a value instead of the existing value (default)
for date and int only:
  • - : subtracts a value from the existing value
No; defaults to =
pattern For int and date type only. If present, values will be parsed and formatted accordingly. No
unit The unit of the value to be applied to date +/- operations. Valid Values are:
  • millisecond
  • second
  • minute
  • hour
  • day (default)
  • week
  • month
  • year
This only applies to date types using a +/- operation.
No; defaults to day

The rules used when setting a property value are shown below. The operation occurs after these rules are considered.


The following changes the file. Assume looks like:

# A string value
akey=original value

# The following is a counter, which will be incremented by 1 for
# each time the build is run.

After running, the file would now look like

#My properties
#Wed Aug 31 13:47:19 BST 2005
# A string value

# The following is a counter, which will be incremented by 1 for
# each time the build is run.

adate=2005/08/31 13\:47 13\:47

The slashes conform to the expectations of the Properties class. The file will be stored in a manner so that each character is examined and escaped if necessary.

The layout and comment of the original file is preserved. New properties are added at the end of the file. Existing properties are overwritten in place.

<propertyfile file=""
              comment="My properties">
    <entry key="akey" value="avalue"/>
    <entry key="adate" type="date" value="now"/>
    <entry key="anint" type="int" default="0" operation="+"/>
    <entry key="" type="int" default="0013" operation="+" pattern="0000"/>
    <entry key="" type="date" value="now" pattern="DDD HH:mm"/>

To produce dates relative from today:

<propertyfile file=""
              comment="My properties">
    <entry key=""
           type="date" default="now" pattern="DDD"
           operation="-" value="1"/>
    <entry key="formated.tomorrow"
           type="date" default="now" pattern="DDD"
           operation="+" value="1"/>

Concatenation of strings:

<propertyfile file=""
              comment="My properties">
    <entrykey="progress" default="" operation="+" value="."/>

Each time called, a . will be appended to progress

Pumps the project version to the next minor version (increase minor and set patch=0):

<target name="nextMinorVersion">
    <property name="header"
              value="##Generated file - do not modify!"/>
    <propertyfile file="" comment="${header}">
        <entry key="" type="int"  value="3"/>
        <entry key="" type="int"  operation="+"/>
        <entry key="" type="int"  value="0"/>
        <entry key=""  type="date" value="now"/>

After running this target the version changed e.g. from 3.2.2 to 3.3.0.