How to log objects to a console with AppleScript

Question

I am just trying to log the state of objects throughout the life of my applescript. In other languages, object's toString() methods will render the text equivalent and I can use those. In AppleScript, this does not seem to be the case.

convert applescript object to string (similar to toString) 

Will output the finder object (and its properties) to the "Results" window of AppleScript Editor, but only if it is the last statement which gets executed.

If I have a trace() statement (which takes a message for logging purposes):

on trace(message) do shell script "cat >>~/log/applescript.txt <<END_OF_THE_LOG " & (message as text) & " END_OF_THE_LOG" end trace 

and try to log the same object, I get

Can’t make properties of application "Finder" into type text. 

I'm open to better ways of logging to a console, but would like to find out how to write an object's properties (like AppleScript Editor does) in the middle of a script for testing either way.

Answer 1

AppleScript doesn't make it easy:

• log only logs while running in AppleScript Editor or when running via osascript (to stderr in that case) - the output will be lost in other cases, such as when applications run a script with the NSAppleScript Cocoa class.

• log only accepts one argument; while it does accept any object type, it doesn't make it easy to get a meaningful representation of non-built-in types: try log me to get information about the script itself, for instance; frequently, log (get properties of <someObj>) must be used to get meaningful information; note the cumbersome syntax, which is required, because just using log properties of <someObj> typically merely prints the name of the reference form instead of the properties it points to (e.g, log properties of me uselessly outputs just (*properties*)).

• In general, AppleScript makes it very hard to get meaningful text representations of objects of non-built-in types: <someObj> as text (same as: <someObj> as string) annoyingly breaks - throws a runtime error - for such objects; try me as text.

Below are helper subroutines that address these issues:

• dlog() is a subroutine that combines deriving meaningful text representations of any objects with the ability to write to multiple log targets (including syslog and files) based on a global config variable.
• toString() (effectively embedded in dlog()) is a subroutine that takes a single object of any type and derives a meaningful text representation from it.

^{Tip of the hat to @1.61803; his answer provided pointers for implementing the various logging targets.}

Examples:

  # Setup: Log to syslog and a file in the home dir.   #        Other targets supported: "log", "alert"   #        Set to {} to suppress logging. set DLOG_TARGETS to { "syslog", "~/as.log" }    # Log properties of the front window of frontmost application. dlog(front window of application (path to frontmost application as text))   # Log properties of own front window; note the *list* syntax for multiple args. dlog({"my front window: ", front window})    # Get properties of the running script as string. toString(me) # ->, e.g.: [script name="sandbox"] {selection:insertion point after character 2475 of text of document "sandbox2.scpt", frontmost:true, class:application, name:"AppleScript Editor", version:"2.6"} 

See the source-code comments above each subroutine for details.

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dlog() source code

    # Logs a text representation of the specified object or objects, which may be of any type, typically for debugging.     # Works hard to find a meaningful text representation of each object.     # SYNOPSIS     #   dlog(anyObjOrListOfObjects)     # USE EXAMPLES     #   dlog("before")  # single object     #     dlog({ "front window: ", front window }) # list of objects     # SETUP     #   At the top of your script, define global variable DLOG_TARGETS and set it to a *list* of targets (even if you only have 1 target).     #     set DLOG_TARGETS to {} # must be a list with any combination of: "log", "syslog", "alert", <posixFilePath>     #   An *empty* list means that logging should be *disabled*.     #   If you specify a POSIX file path, the file will be *appended* to; variable references in the path     #   are allowed, and as a courtesy the path may start with "~" to refer to your home dir.     #   Caveat: while you can *remove* the variable definition to disable logging, you'll take an additional performance hit.     # SETUP EXAMPLES     #    For instance, to use both AppleScript's log command *and* display a GUI alert, use:     #       set DLOG_TARGETS to { "log", "alert" }     # Note:      #   - Since the subroutine is still called even when DLOG_TARGETS is an empty list,      #     you pay a performancy penalty for leaving dlog() calls in your code.     #   - Unlike with the built-in log() method, you MUST use parentheses around the parameter.     #   - To specify more than one object, pass a *list*. Note that while you could try to synthesize a single     #     output string by concatenation yourself, you'd lose the benefit of this subroutine's ability to derive     #     readable text representations even of objects that can't simply be converted with `as text`.     on dlog(anyObjOrListOfObjects)         global DLOG_TARGETS         try             if length of DLOG_TARGETS is 0 then return         on error             return         end try         # The following tries hard to derive a readable representation from the input object(s).         if class of anyObjOrListOfObjects is not list then set anyObjOrListOfObjects to {anyObjOrListOfObjects}         local lst, i, txt, errMsg, orgTids, oName, oId, prefix, logTarget, txtCombined, prefixTime, prefixDateTime         set lst to {}         repeat with anyObj in anyObjOrListOfObjects             set txt to ""             repeat with i from 1 to 2                 try                     if i is 1 then                         if class of anyObj is list then                             set {orgTids, AppleScript's text item delimiters} to {AppleScript's text item delimiters, {", "}} # '                             set txt to ("{" & anyObj as string) & "}"                             set AppleScript's text item delimiters to orgTids # '                         else                             set txt to anyObj as string                         end if                     else                         set txt to properties of anyObj as string                     end if                 on error errMsg                     # Trick for records and record-*like* objects:                     # We exploit the fact that the error message contains the desired string representation of the record, so we extract it from there. This (still) works as of AS 2.3 (OS X 10.9).                     try                         set txt to do shell script "egrep -o '\\{.*\\}' <<< " & quoted form of errMsg                     end try                 end try                 if txt is not "" then exit repeat             end repeat             set prefix to ""             if class of anyObj is not in {text, integer, real, boolean, date, list, record} and anyObj is not missing value then                 set prefix to "[" & class of anyObj                 set oName to ""                 set oId to ""                 try                     set oName to name of anyObj                     if oName is not missing value then set prefix to prefix & " name=\"" & oName & "\""                 end try                 try                     set oId to id of anyObj                     if oId is not missing value then set prefix to prefix & " id=" & oId                 end try                 set prefix to prefix & "] "                 set txt to prefix & txt             end if             set lst to lst & txt         end repeat         set {orgTids, AppleScript's text item delimiters} to {AppleScript's text item delimiters, {" "}} # '         set txtCombined to lst as string         set prefixTime to "[" & time string of (current date) & "] "         set prefixDateTime to "[" & short date string of (current date) & " " & text 2 thru -1 of prefixTime         set AppleScript's text item delimiters to orgTids # '         # Log the result to every target specified.         repeat with logTarget in DLOG_TARGETS             if contents of logTarget is "log" then                 log prefixTime & txtCombined             else if contents of logTarget is "alert" then                 display alert prefixTime & txtCombined             else if contents of logTarget is "syslog" then                 do shell script "logger -t " & quoted form of ("AS: " & (name of me)) & " " & quoted form of txtCombined             else # assumed to be a POSIX file path to *append* to.                 set fpath to contents of logTarget                 if fpath starts with "~/" then set fpath to "$HOME/" & text 3 thru -1 of fpath                 do shell script "printf '%s\\n' " & quoted form of (prefixDateTime & txtCombined) & " >> \"" & fpath & "\""             end if         end repeat     end dlog 

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toString() source code

    # Converts the specified object - which may be of any type - into a string representation for logging/debugging.     # Tries hard to find a readable representation - sadly, simple conversion with `as text` mostly doesn't work with non-primitive types.     # An attempt is made to list the properties of non-primitive types (does not always work), and the result is prefixed with the type (class) name     # and, if present, the object's name and ID.     # EXAMPLE     #       toString(path to desktop)  # -> "[alias] Macintosh HD:Users:mklement:Desktop:"     # To test this subroutine and see the various representations, use the following:     #   repeat with elem in {42, 3.14, "two", true, (current date), {"one", "two", "three"}, {one:1, two:"deux", three:false}, missing value, me,  path to desktop, front window of application (path to frontmost application as text)}     #       log my toString(contents of elem)     #   end repeat     on toString(anyObj)         local i, txt, errMsg, orgTids, oName, oId, prefix         set txt to ""         repeat with i from 1 to 2             try                 if i is 1 then                     if class of anyObj is list then                         set {orgTids, AppleScript's text item delimiters} to {AppleScript's text item delimiters, {", "}}                         set txt to ("{" & anyObj as string) & "}"                         set AppleScript's text item delimiters to orgTids # '                     else                         set txt to anyObj as string                     end if                 else                     set txt to properties of anyObj as string                 end if             on error errMsg                 # Trick for records and record-*like* objects:                 # We exploit the fact that the error message contains the desired string representation of the record, so we extract it from there. This (still) works as of AS 2.3 (OS X 10.9).                 try                     set txt to do shell script "egrep -o '\\{.*\\}' <<< " & quoted form of errMsg                 end try             end try             if txt is not "" then exit repeat         end repeat         set prefix to ""         if class of anyObj is not in {text, integer, real, boolean, date, list, record} and anyObj is not missing value then             set prefix to "[" & class of anyObj             set oName to ""             set oId to ""             try                 set oName to name of anyObj                 if oName is not missing value then set prefix to prefix & " name=\"" & oName & "\""             end try             try                 set oId to id of anyObj                 if oId is not missing value then set prefix to prefix & " id=" & oId             end try             set prefix to prefix & "] "         end if         return prefix & txt     end toString