Variable Syntax¶

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.

File Syntax¶

Substitution variables can be specified in a file. These files consist of lines of the form name=value, name?=value, or name!=value. The = operator assigns a normal substitution variable, the ?= operator (since dpkg 1.21.8) assigns an optional substitution variable which will emit no warnings even if unused, and the != operator (since dpkg 1.22.7) assigns a required substitution variable which will error out if unused. Trailing whitespace on each line, blank lines, and lines starting with a # symbol (comments) are ignored.

Substitution¶

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 common option).

After all the substitutions have been done each occurrence of the string ${} (which is not an actual substitution variable) is replaced with a $ sign. This can be used as an escape sequence such as ${}{VARIABLE} which will end up as ${VARIABLE} on the output.

If a variable is referred to but not defined it generates a warning and an empty value is assumed.

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.

Built-in Variable¶

Additionally, the following standard variables are always available:

Arch

The current host architecture (i.e. the architecture the package is being built for, the equivalent of DEB_HOST_ARCH).

vendor:Name

The current vendor name (since dpkg 1.20.0). This value comes from the Vendor field for the current vendor's origin file, as dpkg-vendor(1) would retrieve it.

vendor:Id

The current vendor ID (since dpkg 1.20.0). This is just the lowercase variant of vendor:Name.

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. With hardlinks only being counted once as a regular file.

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:field-name

The value of the source stanza field field-name (which must be given in the canonical capitalization; 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:field-name

The value of the output field field-name (which must be given in the canonical capitalization). 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).