Linux: ksh condition syntax, e.g. checking result of line count

ksh scripting can be simple to read, but hard to remember the syntax to write it:

# Number of lines in file
    LC=$(wc -l  $DIRNAME/$FILENAME | awk '{print $1}')
    if (("$LC" > 0))
    then
       nonempty file steps
    else
       empty file steps
    fi

• The value looked at has to be in quotes.
• You need to start the "then" on a new line, or have a semicolon before it.
  

  if [ ... ]; then
  

• That's two round parentheses surrounding the condition, because it's numbers not strings comparison.  
• Square brackets are for strings, checking file existence, or value returned from last function

if [[ -f "$DIRNAME/${FILENAME}.txt" ]]
then
...

OK, so I'm finding references to

if (test -d $1)

being the same as

if [-d $1]

and to the use of "-eq" for comparing integers, as in

if [$# -eq 3]

And if you use double square brackets, you avoid triggering an error if your variable is unset.

Good enough for now...