RFC: Packaging Metadata Syntax§

The spec and defines files currently use Bash syntax to define package metadata, which is not easy to parse strictly according to the Bash Reference Manual. Therefore, we propose the use of a reduce set of Bash syntax to reduce parsing and transition cost, as packaging tools will be refactored in languages other than Bash.

Example§

PKGVER=8.2
PKGDEP="x11-lib libdrm expat systemd elfutils libvdpau nettle \
        libva wayland s2tc lm-sensors libglvnd llvm-runtime libclc"
MESON_AFTER="-Ddri-drivers-path=/usr/lib/xorg/modules/dri \
             -Db_ndebug=true" 
MESON_AFTER__AMD64=" \
             ${MESON_AFTER} \
             -Dlibunwind=true"

Permitted Bash Syntax§

• Variable declarations are allowed, eg. a=b.
• Comments: # comment
• Quoting
  • Escape Characters, used in double quotes: \newline, \"
  • Single Quotes, no special meaning inside: 'a'
  • Double Quotes, containes substitutions: "a"
• Shell Expansions
  • Shell Parameter Expansion:
    • ${parameter:offset}: substring
    • ${parameter:offset:length}: substring
    • ${parameter#word}: match shortest prefix and delete
    • ${parameter##word}: match longest prefix and delete
    • ${parameter%word}: match shortest suffix and delete
    • ${parameter%%word}: match longest suffix and delete
    • ${parameter/pattern/string}: replace, once
    • ${parameter//pattern/string}: replace, all

Prohibited Bash Syntax§

All recursion is not allowed.

• Quoting
  • ANSI-C Quoting: $'a\nb'
  • Locale-Specific Translation: $"a"
• Shell Expansions Brace Expansion: a{d,c,b}e
  • Tilde Expansion: ~/.config, for home directory
  • Command Substitution: $(command) or `command` (zip, x264+32, xl2tpd, chibi-scheme, uemacs, llvm, qt-5)
  • Arithmetic Expansion: $(( expression ))
  • Process Substitution: <(list) or >(list)
  • Filename Expansion: must scan directory
  • Shell Parameter Expansion:
    • ${parameter:-word}: when unset, use word
    • ${parameter:=word}: when unset, set word to parameter, and use word
    • ${parameter:?word}: when unset, print word to stderr
    • ${parameter:+word}: when set, use word
    • ${!prefix*}
    • ${!prefix@}
    • ${!name[@]}
    • ${!name[*]}
    • ${#parameter}: get length
    • ${parameter^pattern}: UPPER ONCE
    • ${parameter^^pattern}: UPPE ALL
    • ${parameter,pattern}: lower once
    • ${parameter,,pattern}: lower all
    • ${parameter@operator}: special operations
    • ${parameter/#pattern/string}: replace, only match prefix
    • ${parameter/%pattern/string}: replace, only match suffix

Patterns§

Pattern Matching is only used in ${parameter/pattern/string}. Only * and ? is supported.