Use sh/POSIX expressions

Dockerfile

@@ -6,7 +6,7 @@ COPY . /build
 WORKDIR /build
 ARG DBG=0
 RUN <<EOF
-if [[ $DBG -eq 1 ]]; then
+if [ "$DBG" = 1 ]; then
     go install github.com/go-delve/delve/cmd/dlv@latest
 else
     touch /go/bin/dlv

Dockerfile.dev

@@ -5,7 +5,7 @@ RUN apk add --no-cache git ca-certificates build-base su-exec olm-dev bash jq yq
 COPY . /build
 WORKDIR /build
 ARG DBG=0
-if [[ $DBG -eq 1 ]]; then
+if [ "$DBG" = 1 ]; then
     go install github.com/go-delve/delve/cmd/dlv@latest
 else
     touch /go/bin/dlv

build.sh

@@ -1,5 +1,5 @@
 #!/bin/sh
-if [[ $DBG -eq 1 ]]; then
+if [ "$DBG" = 1 ]; then
     GO_GCFLAGS='all=-N -l'
 else
     GO_LDFLAGS="-s -w ${GO_LDFLAGS}"

docker-run.sh

@@ -36,8 +36,8 @@ fixperms
 
 EXE=/usr/bin/mautrix-whatsapp
 DLV=/usr/bin/dlv
-if [[ -x $DLV ]]; then
-    if [[ $DBGWAIT -ne 1 ]]; then
+if [ -x "$DLV" ]; then
+    if [ "$DBGWAIT" != 1 ]; then
         NOWAIT=1
     fi
     EXE="${DLV} exec ${EXE} ${NOWAIT:+--continue --accept-multiclient} --api-version 2 --headless -l :4040"