util: allow passing commit and checksum through envvars to acquire

notwa-util/acquire

@@ -30,11 +30,17 @@ argue()
         (dest) dest="$rhs" ;; \
         (commit) commit="$rhs" ;; \
         (checksum) checksum="$rhs" ;; \
+        (env) env="${rhs%%[!A-Za-z0-9_]*}" ;; \
         (*) warn "ignoring unknown key: $lhs" ;; \
         esac \
      || exit \
     ;done \
  && { [ "${#from}" != 0 ] || die "missing a required key: from" ;} \
+ &&  if [ -n "$env" ] && [ ".${env#[0-9]}" = ".$env" ] \
+    ;then : \
+        "${commit:="$(printenv "${env}_COMMIT")"}" \
+        "${checksum:="$(printenv "${env}_SHA256")"}" \
+    ;fi \
  &&  if [ "$from" = github ] || [ "$from" = sourcehut ] \
     ;then : \
      && missing key repo "$repo" \
@@ -62,9 +68,7 @@ argue()
  || exit \
  ;}
 
-ok=1 from= repo= commit= checksum=
-
-: \
+ok=1 from= repo= commit= checksum= env= \
  && { [ "$#" == 0 ] || argue "$@" ;} \
  && { [ -d "/tmp" ] || die '/tmp must be mounted (or just exist)' ;} \
  && missing variable dest "$dest" \