A script for MacOS 15 to assist with capturing screenshots of windows. I use this with Claude Code to help usage generate documentation.

capture-window.sh

#!/bin/zsh
# capture-window.sh - Screenshot a specific app window on macOS
#
# Usage: capture-window.sh <app-name> [output-file]
# Examples:
#   capture-window.sh "Google Chrome"
#   capture-window.sh "Google Chrome" ~/Desktop/chrome.png

set -euo pipefail

if [[ $# -lt 1 ]]; then
    echo "Usage: $0 <app-name> [output-file]" >&2
    exit 1
fi

APP_NAME="$1"
OUTPUT="${2:-screenshot_$(date +%Y%m%d_%H%M%S).png}"

# Activate the app to bring its window to the front
osascript -e "tell application \"${APP_NAME}\" to activate"
sleep 0.5

# Get the frontmost window ID via CoreGraphics.
# Uses a small Swift script since CoreGraphics C functions aren't
# accessible from JXA. The app name is passed via env var to avoid
# shell quoting issues.
_TMPFILE=$(mktemp)
trap 'rm -f "$_TMPFILE"' EXIT

cat > "$_TMPFILE" <<'SWIFT'
import CoreGraphics
import Foundation

let appName = ProcessInfo.processInfo.environment["APP_TARGET"] ?? ""
guard let list = CGWindowListCopyWindowInfo(.optionOnScreenOnly, kCGNullWindowID) as? [[String: Any]] else { exit(1) }
for w in list {
    if let name = w["kCGWindowOwnerName"] as? String,
       let layer = w["kCGWindowLayer"] as? Int,
       let num = w["kCGWindowNumber"] as? Int,
       name == appName, layer == 0 {
        print(num)
        break
    }
}
SWIFT

WINDOW_ID=$(APP_TARGET="$APP_NAME" swift "$_TMPFILE" 2>/dev/null)

if [[ -z "$WINDOW_ID" ]]; then
    echo "Error: No window found for '${APP_NAME}'" >&2
    echo "Make sure the app is running and has a visible window." >&2
    exit 1
fi

# -l <id>  capture a specific window by its CGWindowID
screencapture -l "$WINDOW_ID" "$OUTPUT"
echo "Saved: $OUTPUT"