Variables

fobos variables let you define reusable values with a $ prefix and substitute them anywhere in the file, eliminating repetition of paths and flag strings.

Defining variables

Variables are defined in any section by prefixing the option name with $:

[vars]
$SRC    = ./src/
$BUILD  = ./build/
$OBJ    = ./obj/
$MOD    = ./mod/
$CFLAGS = -c -O2 -Wall

Section name

The section containing variables can have any name — [vars], [common-variables], or any other name. The section name is irrelevant; FoBiS.py collects all $-prefixed options from every section.

Using variables

Substitute a variable by referencing its name on the right-hand side of any option:

[modes]
modes = debug release

[vars]
$SRC    = ./src/
$BUILD  = ./build/
$TARGET = ./src/main.f90

[debug]
compiler  = gnu
cflags    = -c -O0 -g
src       = $SRC
build_dir = $BUILD
target    = $TARGET

[release]
compiler  = gnu
cflags    = -c -O3
src       = $SRC
build_dir = $BUILD
target    = $TARGET

Full example

[modes]
modes = shared-lib1 static-lib1 shared-lib2 static-lib2

[common-variables]
$CFLAGS_SHARED = -c -fPIC -O2
$CFLAGS_STATIC = -c -O2
$LFLAGS_SHARED = -shared
$BUILD         = ./build/
$OBJ           = ./obj/
$MOD           = ./mod/

[shared-lib1]
compiler  = gnu
cflags    = $CFLAGS_SHARED
lflags    = $LFLAGS_SHARED
build_dir = $BUILD
obj_dir   = $OBJ
mod_dir   = $MOD
target    = lib1.f90
mklib     = shared

[static-lib1]
compiler  = gnu
cflags    = $CFLAGS_STATIC
build_dir = $BUILD
obj_dir   = $OBJ
mod_dir   = $MOD
target    = lib1.f90
mklib     = static

[shared-lib2]
compiler  = gnu
cflags    = $CFLAGS_SHARED
lflags    = $LFLAGS_SHARED
build_dir = $BUILD
obj_dir   = $OBJ
mod_dir   = $MOD
target    = lib2.f90
mklib     = shared

[static-lib2]
compiler  = gnu
cflags    = $CFLAGS_STATIC
build_dir = $BUILD
obj_dir   = $OBJ
mod_dir   = $MOD
target    = lib2.f90
mklib     = static

Rules and limitations

• Variable names are global — they are collected from all sections before substitution. The one exception is [varset:NAME] sections, whose $-prefixed keys apply only when the named varset is selected; see Varsets.
• Recursion is not allowed — a variable value may not reference another variable.
• Multiple variables can appear in a single option value.
• Variables are substituted via simple string replacement; there is no expression evaluation.
• Overlapping prefixes are safe — substitution respects identifier boundaries, so $HDF5 and $HDF5_PREFIX can coexist in the same fobos without one corrupting the other.

Choosing a binding at invocation time

When several modes differ only in the value a variable should take (cluster paths, GPU architectures, install prefixes), reach for varsets instead of duplicating mode blocks. A varset is a named bundle of $variable bindings selected via --varset NAME on the CLI; the mode block stays cluster-agnostic and binds variables it needs by name. See Varsets for the full reference.

Splitting variables across files

Variables defined in an included fobos file are merged into the implicit global pool exactly as if they had been declared in the main file. This enables patterns like a committed defaults.fobos for project defaults plus an optional, gitignored ?fobos.local for per-developer overrides, layered via a [include] directive.