Using screencapture - how to handle save & filenames

Question

Hello,
i am trying to use screencapture from within applescript-code using do shell script.
so a basic snippet would look like this:
do shell script "screencapture -t png -S /Users/xy/Desktop/foo.png"
Which results in a fullscreen png image on the defined path with the defined filename.
I am wondering about two things right now:
a) how would i manage to just write to filenames like apples shortcuts use for making screenshots ?
Like first image is named: picture 1.png, second picture 2.png ......
b) why is the code above only screenshoting the main screen in case of dual monitor setup. Based on the man page i would expect -m would limit my screenshot to main screen.
Best regards
fidel

Answer 1

a) how would i manage to just write to filenames like apples shortcuts use for making screenshots ?
Like first image is named: picture 1.png, second picture 2.png ......
The first part is trivial - just provide the file name you want to save the file in. The tricky part is ensuring you don't overwrite an existing file. Typically this means you need to check for existing files before determining the filename to use, e.g. (untested):
set file_num to 1
tell application "Finder"
set file_path to (path to desktop as text) & "Picture " & file_num & ".png"
repeat until not exists (file file_path)
set file_num to file_num + 1
end repeat
do shell script "/usr/sbin/screencapture - t png -S " & quoted form of POSIX path of file_path
end tell
The idea here is that you check if the file exists, incrementing the counter until there's no matching file name.
b) why is the code above only screenshoting the main screen in case of dual monitor setup. Based on the man page i would expect -m would limit my screenshot to main screen.
From reading the man page it states:
SYNOPSIS
screencapture [-SWCTMPcimswxt] file
Here you can see the last parameter is files (not file), and furthermore:
files where to save the screen capture, 1 file per screen
I infer from this that you need to provide multiple file names if you have multiple monitors.