Remove preceding and trailing white spaces in string: AppleScript

Question

I'm trying to remove preceding and trailing white spaces in a string but the code I'm using isn't working... It still only works if I select a directory path without white spaces at the beginning or the end. What am I doing wrong?

on run {input, parameters}
    set filePath to input

    set ASTID to AppleScript's AppleScript's text item delimiters
    set AppleScript's text item delimiters to space
    set unwantedSpaces to filePath's text items

    set a to 1
    set b to (count unwantedSpaces)

    repeat while (a < b) and ((count item a of unwantedSpaces) is 0)
        set a to a + 1
    end repeat

    repeat while (b > a) and ((count item b of unwantedSpaces) is 0)
        set b to b - 1
    end repeat

    set strippedText to text from text item a to text item b of filePath
    set AppleScript's AppleScript's text item delimiters to ASTID

    set validFilePaths to {}

    repeat with aLine in strippedText
        try
            set targetAlias to POSIX file aLine as alias
            tell application "Finder" to reveal targetAlias
            set end of validFilePaths to {}

        end try
    end repeat
    return validFilePaths
end run

Answer 1

Similar to double_j's answer, but for others who land here...

I often use a simple sub-routine, with echo " str1 " | xargs shell script:

on trim(theText)
  return (do shell script "echo \"" & theText & "\" | xargs")
end trim

OR because JavaScript is my typical language I sometimes think in JS & do this (even though it's terribly inefficient, so I wouldn't use this for trim but it can be a quick win for more complex things when being efficient isn't critical):

on trim(theText)
  return (do shell script "osascript -l JavaScript -e '\"" & theText & "\".trim()'")
end trim

(Perhaps there's a real way to execute inline JS in AppleScript, but I'm not sure......yet)

Answer 2

Here's another simpler approach:

on run {input, parameters}
    set filePath to input as text
    set Trimmed_filePath to do shell script "echo " & quoted form of filePath & " | sed -e 's/^[ ]*//' | sed -e 's/[ ]*$//'"
end run