How to log objects to a console with AppleScript

Solution 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.

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

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

Solution 2:

Just use the log statement in AppleScript Editor. When you view the results in Applescript Editor, at the bottom of the window press the "Events" button. Normally the "Results" button is pressed and then you only see the result of the last statement as you mention. So change the button to "Events". This will show you everything that is happening as the script runs, and additionally all of the log statements that you put throughout the code too. Note that the log statements do not have to be text. You can log any object.

This is the best way to debug your script and see what is happening. As an example try this and look at the "Events". Realistically thought you don't need a lot of log statements if you view the Events because everything is already logged!

set someFolder to path to desktop
log someFolder

tell application "Finder"
    set someItem to first item of someFolder
    log someItem

    set itemProps to properties of someItem
    log itemProps
end tell