bandwidth monitor script for i3blocks

bandwidth.sh

#!/bin/bash

if [ "$1" != "" ]; then
    echo "Missing required argument: 'tx' or 'rx'" 1>&2
    exit 1
fi
if [ "$1" != "rx" -a "$1" != "tx" ]; then
    echo "Invalid argument: $1" 1>&2
    echo "Usage: $0 (rx|tx)" 1>&2
    exit 1
fi

DIRECTION=$1
TMPFILE=/dev/shm/i3blocks_bandwidth_$DIRECTION
touch $TMPFILE

PREV=$(cat $TMPFILE)
NETDIR=/sys/class/net
IFACE=$(ip r | grep default | cut -d' ' -f5)
FILE=$NETDIR/$IFACE/statistics/${DIRECTION}_bytes
CUR=$(cat $FILE)
DELTA=$(expr $CUR - $PREV)

echo $(expr $DELTA / 1000) kB/s

echo $CUR > $TMPFILE
                                                                                             

Two suggestions/remarks:

1. Shouldn't line 3 check if $1 is equal to nothing, rather than unequal?
2. It doesn't play nice if you have multiple interfaces. You could remove any extra line ip r | grep default returns. (I solved it quickly by appending | head -n 1, but perhaps there's a better way).

I believe there is a typo on line 3, it should be if [ "$1" == "" ]; then

It is a type, it will never run with line 3 the way it is.
I would also suggest replacing line 15 with

if [ ! -f $TMPFILE ]; then
   echo '0' > $TMPFILE
fi

to avoid expr: syntax error warnings on the very first run.

Hey @joehillen,

In case you haven't heard, i3blocks is splitting into two repos! i3blocks will now go on to contain the core binary and a set of smallest usable blocklets to provide some beginner functionality. From i3blocks, i3blocks-contrib has now split off to gather the community contributed blocklets in a single repo to make perusing them easier and more convenient. We would be honoured if you would consider submitting your blocklet(s) to the contrib repo.

This change is the core change scheduled for the v1.5 release. Please note that as an artifact of this split, your entry for this blocklet in the core wiki has been removed as has everyone else's. If you would like to submit your blocklet, please review the contrib wiki to understand the workflow of i3blocks-contrib.

Please note that this change over is in its early stages, so the process for submission hasn't been completely nailed down. We're hard at work still compiling the two project wikis and documenting all changes and standards. It is very likely that things will still change and we value your input on how that change should occur.

Deepest regrads,

@Nycroth