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telem-seq.sh: Make compatible to busybox sh #180

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telem-seq.sh: Make compatible to busybox sh #180

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telem-seq.sh: Make compatible to busybox sh 
busybox's sh-implementation is differnt from the normal sh:

In busybox-expr an empty string does not evaluate to int(0).
Calling `expr ($SEQ +1)` with `SEQ=""` fails.

This patch works around this behavior by making sure the file
exists.

I left the pipe for stderr around the `cat` in place to make
sure I do not break any other error cases.

Signed-off-by: Chris Fiege <chris@tinyhost.de>
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@SmithChart
SmithChart committed Nov 20, 2018
commit 5eb7ae6a194ec1b5f13d6e94a493b42e883af6dd
6 changes: 5 additions & 1 deletion telemetry-toolkit/telem-seq.sh
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Expand Up @@ -2,6 +2,10 @@
# Generate sequence number as described here:
# https://github.com/wb2osz/direwolf/issues/9
#
if [ ! -f /tmp/seq ]; then
echo 0 > /tmp/seq
fi

SEQ=`cat /tmp/seq 2>/dev/null`
SEQ=$(expr \( $SEQ + 1 \) % 1000)
echo $SEQ | tee /tmp/seq
echo $SEQ | tee /tmp/seq