Creating charts for my UPS metrics - Part 2

Question

Following up from my previous question

Streaming my UPS metrics for graphical viewing in bash

#!/usr/bin/env bash

[ -v METRICS_CHECK ] && set -x

API_URL="https://api.thingspeak.com/update"
UPS_PROPS=("LINEV" "LOADPCT" "TIMELEFT")
API_PARAMS=("api_key==XXXXXXXXXXXXXX")

for index in "${!UPS_PROPS[@]}"
do
    value=$(/sbin/apcaccess -up "${UPS_PROPS[$index]}")
    field=$((index + 1))
    if [ "$field" -eq 2 ]
        then
        # bc required for floating point arithmetic
        value=$(echo "$value * 6" | bc)  # 600 Watt * load percent
    fi
    PARAM=$(printf "field%d==%s" "$field" "$value")
    API_PARAMS+=("${PARAM}")
done

/usr/local/bin/http "$API_URL" ${API_PARAMS[@]}

Updates:

• Collects data for different metrics supported by apcaccess
• Use a variable check for enabling debug mode
• Split parameters sent to API URL into a different array
• Move away from curl to use httpie
• Custom computation for certain attributes

---

The shellcheck passes everything except the unquoted ${API_PARAMS[@]} in the last line. I am not sure that httpie would work if I quote that and pass it as a single argument.

---

Charts for viewing pleasure (last 600 minutes data from the time post was created):

1. Input line voltage

   

2. Load (in wattage) on the UPS

   

3. Battery time left for the UPS

   

Click the images to get live charts.

Answer 1

Quoting - you need double-quotes on the last line: it should be "${API_PARAMS[@]}" (remember that the [@] makes the shell expand it into multiple words, so it won't be seen by your http program as just one).

Instead of if [ "$field" -eq 2 ], it's clearer to compare the field name. That will help if you change the properties list in future. It may help to create a variable:

propname="${UPS_PROPS[$index]}"
value=$(/sbin/apcaccess -up "$propname")
if [ "$propname" = LOADPCT ]

We can supply standard input from a string without needing an echo process, by using <<< redirection:

    # bc required for floating point arithmetic
    value=$(<<<"$value * 6" bc)  # 600 Watt * load percent

We can make the array 1-based, and avoid the need to have $field different from $index:

UPS_PROPS=([1]="LINEV" "LOADPCT" "TIMELEFT")