allan.jacobs@Eng 1998-06-01

The man pages mention the -m option but do not motivate it.

     To use a pre-existing manifest file to create a new jar
     archive, specify the old manifest file with the -m option:

          example% jar cmf myManifestFile myJarFile *.class

Why anyone would want to do this is absolutely opaque. There is
information in bugtraq bug reports, but these should not be the repository
of the documentation for the jar command.

A pre-existing manifest file can contain customized headers
that can be used to describe and label the contents of the jar
file.

The default jar manifest for one of the tests that I am working with
looks like this
% jar -xvf one.jar META-INF/MANIFEST.MF
% cat META-INF/MANIFEST.MF
Manifest-Version: 1.0
Created-By: Manifest JDK 1.2

Name: classes/SecurityTestApplet.class
SHA-Digest: mgXxI1aa9Y1pM2G6h6aSHkZf66w=

Name: classes/SecurityTest.class
SHA-Digest: koEViVBN7JJR86uhl7IzI5hAxLU=

Name: classes/GetAudioTest.class
SHA-Digest: M2nVAaV/GUiGpw0qYAkv3jhplBM=

Name: classes/PackageImportTest.class
SHA-Digest: UQJuuqzHwYR6d9xjLxpuuKZ2rh8=

Name: classes/GetImageTest.class
SHA-Digest: rOORt9Bb+uRg05IlC4+Hx2HkVvc=

Name: images/javalogo52x88.gif
SHA-Digest: ygISCp2ogX4jA7ocxNLx52Z+PaY=

Name: audio/spacemusic.au
SHA-Digest: 0catQiIinPAGeJ4Gmk60BcHQmWM=

Name: GetAudioTest.java
SHA-Digest: kMKQlZSWlvV3EbSR2XcrcAFyItI=

Name: GetImageTest.java
SHA-Digest: nBegdvZ+L6EwLg80KY9clDGKYxg=

Name: PackageImportTest.java
SHA-Digest: /JELPE0twd0BiGutLh97dj4IZ2I=

Name: SecurityTest.java
SHA-Digest: odQ3AQnCrecRIDSlWaR7v4ayx3M=

Name: SecurityTestApplet.java
SHA-Digest: Fb9tbUV9g5hfwG1EeBIowkQ7ZJE=


The manifest could contain custom headings that contain useful information.
In the example below, an Author field is added. This annotated manifest
can be used, instead of the default, if the command line used to create
the jar file makes use of the -m option.

% jar -cmf myMANIFEST.MF two.jar classes images audio *.java


Manifest-Version: 1.0
Author: Homer
Created-By: Manifest JDK 1.2

Name: classes/SecurityTestApplet.class
Author: Dante
SHA-Digest: mgXxI1aa9Y1pM2G6h6aSHkZf66w=

Name: classes/SecurityTest.class
Author: Shakespeare
SHA-Digest: koEViVBN7JJR86uhl7IzI5hAxLU=

Name: classes/GetAudioTest.class
Author: Cervantes
SHA-Digest: M2nVAaV/GUiGpw0qYAkv3jhplBM=

Name: classes/PackageImportTest.class
Author: Hesiod
SHA-Digest: UQJuuqzHwYR6d9xjLxpuuKZ2rh8=

Name: classes/GetImageTest.class
Author: Ovid
SHA-Digest: rOORt9Bb+uRg05IlC4+Hx2HkVvc=

Name: images/javalogo52x88.gif
Author: Pollack
SHA-Digest: ygISCp2ogX4jA7ocxNLx52Z+PaY=

Name: audio/spacemusic.au
Author: Mozart
SHA-Digest: 0catQiIinPAGeJ4Gmk60BcHQmWM=

Name: GetAudioTest.java
Author: Melville
SHA-Digest: kMKQlZSWlvV3EbSR2XcrcAFyItI=

Name: GetImageTest.java
Author: Swift
SHA-Digest: nBegdvZ+L6EwLg80KY9clDGKYxg=

Name: PackageImportTest.java
Author: Goethe
SHA-Digest: /JELPE0twd0BiGutLh97dj4IZ2I=

Name: SecurityTest.java
Author: Joyce
SHA-Digest: odQ3AQnCrecRIDSlWaR7v4ayx3M=

Name: SecurityTestApplet.java
Author: Anonymous
SHA-Digest: Fb9tbUV9g5hfwG1EeBIowkQ7ZJE=