Convert a file mode string into the octal value

perm2octal.sh

#!/bin/bash

# Convert a file mode string (e.g., -rw-rw-r--) into the octal value

function perm2octal()
{
  local perm=${1:1} # remove first char (the file type)

  res=$(echo "$perm" | sed 's/[^-]/1/g; s/-/0/g')
  res=$(echo "ibase=2; obase=8; $res" | bc)

  echo "$res"
}