Prompt existing overwrites when using lnav -i <file>

[lamchau]

Is your feature request related to a problem? Please describe.
Running lnav -i <file> to install log definitions will clobber an existing ones. Generally this is preferred but when sharing definitions to other users (in a team setting) who edit the "base format" to add their own customizations may inadvertently lose them.

Context: This is usually user error but adding a small quality of life improvement to prevent destructive format installs would be a nice addition. A contrived but plausible scenario is running lnav -i $XDG_CONFIG_HOME/lnav/formats/installed foo.json will yield a 0 length file.

Describe the solution you'd like
Prompt the user that an format definition already exists and give them a chance to bail/overwrite. It should print out the absolute path so it's fast to backup/edit.

Note: I'm not sure how this would adversely impact lnav -i extras since that might be expected (as an update). But that's extra work that's probably not needed.

Describe alternatives you've considered
Workaround using a bootstrapping script

lnav_format="$(lnav -m format my_json_log source 2> /dev/null)"
if [ -n "$lnav_format" ]; then
  confirm="n"
  echo "warning: my_json_log format already exists '$lnav_format'"
  read -r -p "overwrite? [y/n] " confirm
  if [[ "$confirm" =~ [NnQq] ]]; then
    exit 0
  fi
fi

[tstack]

Good catch, thanks for raising the issue. I pushed a change that adds some more checks to the installation path:

• Writing the file is proper now, it writes to a temp file and then renames it over the destination path;
• If the source and destination are the same, nothing is done;
• If there is a destination, and it's different, the old files is renamed with '.bak' at the end and a note is included in the success message