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.. _tcl2lua-label:
How does Lmod convert TCL modulefile into Lua
=============================================
Lmod uses a TCL program called **tcl2lua.tcl** to read TCL modulefiles
and convert them to lua. The whole TCL modulefile evaluated by the
TCL interpreter. This is *NOT* a source to source translation.
The purpose of **tcl2lua.tcl** is to evaluate the regular TCL command
but replace "module functions", such as **prepend-path** or
**setenv**, and converted to Lua functions. For example, suppose you have
the following simple TCL modulefile for git::
#%Module
set appDir $env(APP_DIR)
set version 2.0.3
prepend-path PATH "$appDir/git/$version/bin"
Assuming that the environment variable APP_DIR is */apps* then the
entire output of the **tcl2lua.tcl** program would be::
prepend_path("PATH", "/apps/git/2.0.3/bin")
Note that all the normal TCL code has been evaluated and the TCL
**prepend-path** command has been converted to a lua **prepend_path**
function call.
Normally this works fine. However, because Lmod does evaluate the
actions of a TCL module file as a two-step process, it can cause
problems. In particular, suppose you have two TCL modulefiles:
Centos::
#%Module
setenv SYSTEM_NAME Centos
And B::
#%Module
module load Centos
if { $env(SYSTEM_NAME) == "Centos" } {
# do something
}
When Lmod tries to translate the B modulefile into lua it fails::
load("Centos")
LmodError([[/opt/mfiles/B: (???): can't read "env(SYSTEM_NAME)": no such variable]])
This is because unlike the TCL/C Module system, the **module load
Centos** command is converted to a function call, but it won't load the module
in time for the test to be evaluated properly.
The only solution is convert the B modulefile into a Lua modulefile (B.lua)::
load("Centos")
if (os.getenv("SYSTEM_NAME") == "Centos") then
-- Do something
end
The Centos modulefile does not have to be translated in order for this to
work, just the B modulefile.
As a side note, you are free to put Lua modules in the same tree that the
TCL/C Module system uses. It will ignore files that the first line is
not #%Module and Lmod will pick B.lua over B.
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