#!/bin/bash
# verifycron--Checks a crontab file to ensure that it's
#    formatted properly. Expects standard cron notation of
#       min hr dom mon dow CMD,    
#    where min is 0-59, hr is 0-23, dom is 1-31, mon is 1-12 (or names)
#    and dow is 0-7 (or names). Fields can be ranges (a-e) or lists
#    separated by commas (a,c,z) or an asterisk. Note that the step 
#    value notation of Vixie cron (e.g., 2-6/2) is not supported by 
#    this script in its current version.


proc validNum
{
  # Return 0 if the number given is a valid integer and 1 if not. 
  # Specify both number and maxvalue as args to the function.
  setglobal num = $1,   max = $2

  # Asterisk values in fields are rewritten as "X" for simplicity,
  #   so any number in the form "X" is de facto valid.

  if test $num = "X"  {
    return 0
  } elif test ! -z $[echo $num | sed 's/[[:digit:]]//g]  {
    # Stripped out all the digits, and the remainder isn't empty? No good.
    return 1
  } elif test $num -gt $max  {
    # Number is bigger than the maximum value allowed.
    return 1
  } else {
    return 0
  }
}

proc validDay
{
  # Return 0 if the value passed to this function is a valid day name, 
  #   1 otherwise.

  match $[echo $1 | tr '[:upper:]' '[:lower:]] {
    with sun*|mon*|tue*|wed*|thu*|fri*|sat* return 0 
    with X return 0          # Special case--it's a rewritten "*"
    with * return 1
  }
}

proc validMon
{
  # This function returns 0 if given a valid month name, 1 otherwise.

   match $[echo $1 | tr '[:upper:]' '[:lower:]] { 
     with jan*|feb*|mar*|apr*|may|jun*|jul*|aug* return 0           
     with sep*|oct*|nov*|dec*                    return 0           
     with X return 0  # special case, it's an "*"
     with * return 1        
   }
}

proc fixvars
{
  # Translate all '*' into 'X' to bypass shell expansion hassles.
  # Save original input as "sourceline" for error messages.

  setglobal sourceline = ""$min $hour $dom $mon $dow $command""
   setglobal min = $[echo $min | tr '*' 'X]      # minute
  setglobal hour = $[echo $hour | tr '*' 'X]     # hour
   setglobal dom = $[echo $dom | tr '*' 'X]      # day of month
   setglobal mon = $[echo $mon | tr '*' 'X]      # month
   setglobal dow = $[echo $dow | tr '*' 'X]      # day of week
}

if test $Argc -ne 1 || test ! -r $1  {
  # If no crontab filename is given or it's not readable by the script, fail.
  echo "Usage: $0 usercrontabfile" > !2; exit 1
}

setglobal lines = '0',  entries = '0',  totalerrors = '0'

# Go through the crontab file line by line, checking each one.

while read min hour dom mon dow command
{
  setglobal lines = "$shExpr(' $lines + 1 ')" 
  setglobal errors = '0'
  
  if test -z $min -o $(min%${min#?}) = "#"  {
    # If it's a blank line or the first character of the line is "#", skip it.
    continue    # Nothing to check
  }


  sh-expr 'entries++'

  fixvars

  # At this point, all the fields in the current line are split out into
  # separate variables, with all asterisks replaced by "X" for convenience,
  # so let's check the validity of input fields...

  # Minute check

  for minslice in [$[echo $min | sed 's/[,-]/ /g]]  {
    if ! validNum $minslice 60  {
      echo "Line $(lines): Invalid minute value \"$minslice\""
      setglobal errors = '1'
    }
  }

  # Hour check
  
  for hrslice in [$[echo $hour | sed 's/[,-]/ /g]]  {
    if ! validNum $hrslice 24  {
      echo "Line $(lines): Invalid hour value \"$hrslice\"" 
      setglobal errors = '1'
    }
  }

  # Day of month check

  for domslice in [$[echo $dom | sed 's/[,-]/ /g]]  {
    if ! validNum $domslice 31  {
      echo "Line $(lines): Invalid day of month value \"$domslice\""
      setglobal errors = '1'
    }
  }

  # Month check: Has to check for numeric values and names both.
  #   Remember that a conditional like "if ! cond" means that it's
  #   testing whether the specified condition is FALSE, not true.

  for monslice in [$[echo $mon | sed 's/[,-]/ /g]]  {
    if ! validNum $monslice 12  {
      if ! validMon $monslice  {
        echo "Line $(lines): Invalid month value \"$monslice\""
        setglobal errors = '1'
      }
    }
  }

  # Day of week check: Again, name or number is possible.

  for dowslice in [$[echo $dow | sed 's/[,-]/ /g]]  {
    if ! validNum $dowslice 7  {
      if ! validDay $dowslice  {
        echo "Line $(lines): Invalid day of week value \"$dowslice\""
        setglobal errors = '1'
      }
    }
  }

  if test $errors -gt 0  {
    echo ">>>> $(lines): $sourceline"
    echo ""
    setglobal totalerrors = "$shExpr(' $totalerrors + 1 ')"
  }
} < $1 # read the crontab passed as an argument to the script

# Notice that it's here, at the very end of the "while" loop, that we
#   redirect the input so that the user-specified filename can be 
#   examined by the script!

echo "Done. Found $totalerrors errors in $entries crontab entries."

exit 0