Writing some bash scripts that parse command lines, I wrote this handy template with getopt. It is easy to apply even for simplest scripts.

OPTION_SPEC="help,flag1,flag2_params:"
PARSED_OPTIONS=$(getopt -n "$0" -a -o h --long $OPTION_SPEC -- "$@")
OPTIONS_RET=$?
eval set -- "$PARSED_OPTIONS"


Parsing error or no flags

if [ $OPTIONS_RET -ne 0 ] || [ $# -le 0 ]; then
  usage;
  die;
fi

while [ $# -ge 1 ]; do
  case $1 in
    --help | -h )  usage; die;;
    --flag1 )  FLAG1=1;;
    --flag2_params )  shift; FLAG2_PARAMS="$1";;
    -- ) shift;;
    * ) echo "ERROR: unknown flag $1"; usage; die;;
  esac
  shift
done

No more unannotated $ns in my scripts!

I recently had to hack a small shell script that would read files in a directory structure generated based on the date, something like 2007/08/16. The trick was that the script would look at yesterday’s file or files generated a few days ago.

A quick search on info and here’s the magic command

FILE="...$(date -d 'yesterday' +%Y/%m/%d)"

Interestingly, you can also use things like 3 days ago, next Monday, 2 months etc. Cool!