| deb-substvars(5) | dpkg suite | deb-substvars(5) |
deb-substvars - Debian source substitution variables
debian/substvars, debian/binary-package.substvars, variables
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.
Substitution variables can be specified in a file. These files consist of lines of the form name=value or name?=value. The = operator assigns a normal substitution variable, while the ?= operator (since dpkg 1.21.8) assigns an optional substitution variable which will emit no warnings even if unused. Trailing whitespace on each line, blank lines, and lines starting with a # symbol (comments) are ignored.
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.
Additionally, the following standard variables are always available:
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.
dpkg(1), dpkg-vendor(1), dpkg-genchanges(1), dpkg-gencontrol(1), dpkg-shlibdeps(1), dpkg-source(1).
| 2024-09-26 | 1.22.6 |