prepareEnv,checkEnv refactor; other tiny fixes

nixos-infect

@@ -1,6 +1,6 @@
 #! /usr/bin/env bash
 
-# Use Digital Ocean Droplet image:
+# These are the only supported Digital Ocean images:
 #
 #     Fedora 24 x64
 #     Ubuntu 16.04 x64
@@ -45,10 +45,7 @@
 # simply didn't work for me! (old system was being because grub wasnt properly
 # reinstalled)
 
-set -ex
+set -ex -o pipefail
-
-export disk=$( (>/dev/null ls -l /dev/vda && echo vda) \
-   || (>/dev/null ls -l /dev/sda && echo sda) ) 
 
 makeConf() {
   # NB <<"EOF" quotes / $ ` in heredocs, <<EOF does not
@@ -142,6 +139,7 @@ EOF
 }
 
 makeSwap() {
+  # TODO check currently available swapspace first
   swapFile=`mktemp`
   dd if=/dev/zero of=$swapFile bs=1M count=$((1*1024))
   chmod 0600 $swapFile
@@ -149,18 +147,35 @@ makeSwap() {
   swapon $swapFile
 }
 
-makeConf
+prepareEnv() {
-makeSwap # smallest (512MB) droplet needs extra memory!
-
   which dnf && dnf install -y perl-Digest-SHA # Fedora 24
   which bzcat || (which yum && yum install -y bzip2) # CentOS
 
+  # $disk is used in makeConf()
+  disk=$( (test -e /dev/vda && echo vda)
+       || (test -e /dev/sda && echo sda) )
+
   # DigitalOcean doesn't seem to set USER while running user data
   export USER="root"
   export HOME="/root"
 
+  # FIXME run only if necessary
   groupadd -r nixbld -g 30000 || true
   seq 1 10 | xargs -I{} useradd -c "Nix build user {}" -d /var/empty -g nixbld -G nixbld -M -N -r -s `which nologin` nixbld{} || true
+}
+
+checkEnv() {
+  # TODO: use wget -O- if available instead of curl. This involves patching the
+  # /nix/install script to not check for curl and use `wget -O` instead of
+  # `curl -L # -o`
+  ( which curl  || echo "ERROR: Missing curl"  ) && \
+  ( which bzcat || echo "ERROR: Missing bzcat" ) && \
+  ( which perl  || echo "ERROR: Missing perl"  )
+}
+
+infect() {
+  makeConf
+  makeSwap # smallest (512MB) droplet needs extra memory!
 
   curl https://nixos.org/nix/install | sh
 
@@ -196,5 +211,7 @@ EOF
 
   rm -rf /boot.bak && mv -v /boot /boot.bak &&
     /nix/var/nix/profiles/system/bin/switch-to-configuration boot
+}
 
-reboot
+prepareEnv
+checkEnv && infect && reboot