Continue an SFK script at a different point, or stop the script due to a condition with sfk if.

sfk ... +if [opts] expression command1 ... +command2
sfk ... +if expr [+]begin +cmd1a +cmd1b ... +endif +cmd2

execute command1 if expression is true, then continue to command2.
if expression is not true, skip directly to command2.
can be used only in a command chain, after another command.

use "+if expr +begin ... +endif" to run multiple commands
as one block, if expression is true.

supported expressions

   return code comparison
   "rc=n"     return code of previous command equal  to   n
   "rc>n"     return code of previous command higher than n
   "rc<n"     return code of previous command lower  than n
   "rc<>n"    return code of previous comm.  not equal to n

   generic text or number comparison
   "l = r"    left part is equal to right
   "l <> r"   left part is not equal to right
   "l < r"    left part is lower  then right
   "l > r"    left part is higher then right
   "l <= r"   left part is lower  or equal
   "l >= r"   left part is higher or equal
   if both l and r contain only digits a numeric
   comparison is done, else a text comparison.

options
   options for if must be given before expression.
   -var       use sfk variables, must be first option.
   -text      force text comparison (nocase)
   -case      case sensitive text comparison
   -debug     tell what is done in a generic comparison

chaining support
   since sfk 1.7.7 this command no longer consumes
   text input from the command chain.

see also
   sfk call  call sub functions in a script.
   sfk goto  jump to a local label.

examples
   sfk filter in.txt -+err +if "rc>0" run -yes "x.bat" +echo done
      if file in.txt contains the word "err", run x.bat.
      the "echo done" is always executed.

   sfk xex -justrc in.txt "/foo*bar/"
    +if "rc=0" stop 9 "[Red]error:[def] miss" +echo "match"
      type this all in one line, or use "sfk cmd 18". [18]
      if file in.txt does not contain the search pattern
      then stop with return code 9, printing an error.