Before dpkg-source, dpkg-gencontrol and dpkg-genchanges write
their control information (to the source control file .dsc for
dpkg-source and to standard output for dpkg-gencontrol and
dpkg-genchanges) they perform some variable substitutions on the
output file.
A variable substitution has the form ${variable-name}. Variable
names consist of alphanumerics (a-zA-Z0-9), hyphens (-) and
colons (:) and start with an alphanumeric, and are case-
sensitive, even though they might refer to other entities which
are case-preserving. Variable substitutions are performed
repeatedly until none are left; the full text of the field after
the substitution is rescanned to look for more substitutions.
After all the substitutions have been done each occurrence of the
string ${} (which is not a legal substitution) is replaced with a
$ sign.
While variable substitution is done on all control fields, some
of those fields are used and needed during the build when the
substitution did not yet occur. That's why you can't use
variables in the Package, Source and Architecture fields.
Variable substitution happens on the content of the fields after
they have been parsed, thus if you want a variable to expand over
multiple lines you do not have to include a space after the
newline. This is done implicitly when the field is output. For
example, if the variable ${Description} is set to "foo is
bar.${Newline}foo is great." and if you have the following field:
Description: foo application
${Description}
.
More text.
It will result in:
Description: foo application
foo is bar.
foo is great.
.
More text.
Variables can be set using the -V common option. They can be also
specified in the file debian/substvars (or whatever other file is
specified using the -T option). This file consists of lines of
the form name=value. Trailing whitespace on each line, blank
lines, and lines starting with a # symbol (comments) are ignored.
Additionally, the following standard variables are available:
Arch The current host architecture (i.e. the architecture the
package is being built for, the equivalent of
DEB_HOST_ARCH).
source:Version
The source package version (since dpkg 1.13.19).
source:Upstream-Version
The upstream source package version, including the Debian
version epoch if any (since dpkg 1.13.19).
binary:Version
The binary package version (which may differ from
source:Version in a binNMU for example; since dpkg
1.13.19).
Source-Version
The source package version (from the changelog file). This
variable is now obsolete and emits an error when used as
its meaning is different from its function, please use the
source:Version or binary:Version as appropriate.
source:Synopsis
The source package synopsis, extracted from the source
stanza Description field, if it exists (since dpkg
1.19.0).
source:Extended-Description
The source package extended description, extracted from
the source stanza Description field, if it exists (since
dpkg 1.19.0).
Installed-Size
The approximate total size of the package's installed
files. This value is copied into the corresponding control
file field; setting it will modify the value of that
field. If this variable is not set dpkg-gencontrol will
compute the default value by accumulating the size of each
regular file and symlink rounded to 1 KiB used units, and
a baseline of 1 KiB for any other filesystem object type.
Note: Take into account that this can only ever be an
approximation, as the actual size used on the installed
system will depend greatly on the filesystem used and its
parameters, which might end up using either more or less
space than the specified in this field.
Extra-Size
Additional disk space used when the package is installed.
If this variable is set its value is added to that of the
Installed-Size variable (whether set explicitly or using
the default value) before it is copied into the
Installed-Size control file field.
S:fieldname
The value of the source stanza field fieldname (which must
be given in the canonical capitalisation; since dpkg
1.18.11). Setting these variables has no effect other
than on places where they are expanded explicitly. These
variables are only available when generating binary
control files.
F:fieldname
The value of the output field fieldname (which must be
given in the canonical capitalisation). Setting these
variables has no effect other than on places where they
are expanded explicitly.
Format The .changes file format version generated by this version
of the source packaging scripts. If you set this variable
the contents of the Format field in the .changes file will
change too.
Newline, Space, Tab
These variables each hold the corresponding character.
shlibs:dependencyfield
Variable settings with names of this form are generated by
dpkg-shlibdeps.
dpkg:Upstream-Version
The upstream version of dpkg (since dpkg 1.13.19).
dpkg:Version
The full version of dpkg (since dpkg 1.13.19).
If a variable is referred to but not defined it generates a
warning and an empty value is assumed.
