How can I check (and delete) if the last line (that contains the last occurence of a string) has a comma as last character?

I’ve been looking all over the internet but had no result.

I’m trying to build a package generator (in shell/bash) and that respective package contains (one or more) json files. When browsing through a json file, if the user wants to delete one of the steps I must first take into consideration what if the step he wants to delete is the last. If so, the previous of the last step will contain a comma, but the json format does not permit that.

{
  "operation_machinetype": "Ford",
  "operation_steps": [
    "steps/Step_1/01_paint_the_car.json",
    "steps/Step_2/01_drive_the_car.json",
    "steps/Step_2/02_park_the_car.json"
  ]
}

Example, If I delete ‘”steps/Step2/02_park_the_car.json”‘, then ‘”steps/Step2/01_drive_the_car.json”,’ will be the last step, but the comma will then cause an error.

Thank you in advance everyone.

Answer

$ cat tst.awk
index($0,tgt) {
    if (!/,[[:space:]]*$/) {
        sub(/,[[:space:]]*$/,"",prev)
    }
    next
}
NR>1 { print prev }
{ prev = $0 }
END { print prev }

$ awk -v tgt='"steps/Step_2/02_park_the_car.json"' -f tst.awk file
{
  "operation_machinetype": "Ford",
  "operation_steps": [
    "steps/Step_1/01_paint_the_car.json",
    "steps/Step_2/01_drive_the_car.json"
  ]
}

$ awk -v tgt='"steps/Step_2/01_drive_the_car.json"' -f tst.awk file
{
  "operation_machinetype": "Ford",
  "operation_steps": [
    "steps/Step_1/01_paint_the_car.json",
    "steps/Step_2/02_park_the_car.json"
  ]