HACKING

Care and feeding of your initramfs generator
--------------------------------------------

This guide attempts to outline the style used in the mkinitcpio codebase.


Bash v. POSIX
-------------
Never use POSIX syntax if Bash offers a construct of its own, even if the
two are effectively identical. This means always using double braces over
the inferior '[' and 'test'.


Variable usage and naming conventions
------------------------------------
There are three classifications of variables in mkinitcpio.

1) local variables: all lower case, and scoped within functions. Use
freely, as they're well contained. Unless you're introducing a new
option, this is what you want to use.

  local foo=$1

2) global variables: these are known to mkinitcpio internally, but are
global in scope. They carry runtime configuration and data collected during the
image generation process. These are always lower case, but carry a leading
underscore to denote that they're global. It's helpful to prefix these
variables instead with a '_f_' or '_d_' if they refer to a file or directory,
respectively.

  _optcolor=1
  _d_hookdir=/etc/foo.d
  _f_config=/etc/foo.conf

3) "API" variables: also global in scope, but exist "outside" of
mkinitcpio -- either drawn in from the configuration file, or "exported"
to the install hooks. These are always all upper case. When introducing
new variables, extreme care must be taken to pick names that will not
conflict with the environment inherited by mkinitcpio.

Function naming
---------------
Use all lower case with underscores where appropriate, for easy readability.
Adhere to POSIX variable naming requirements for the contents of the name,
that is: only alphanumerics, underscores, and the identifier must not start
with a number.


Quoting
-------
Overquoting is preferred to underquoting, but freely avoid quoting in the
cases when expansion is guaranteed not to happen, such as in single argument
test expressions or the subject of a case statement.


Functions and block statements
------------------------------
Always use "top-right, "lower left" for blocks of code and functions.

  do_glob() {
    local g fn=$1; shift

    for g in "$@"; do
      "$fn" "$g"
    done
  }