fix: Copy pipe usage

copy

@@ -1,32 +1,28 @@
 #!/bin/bash
 
-# Copy file contents to clipboard
+# Copy file contents or command output to clipboard
 # Usage: copy <file>
-#        ... | copy <file_name>
+#        ... | copy
 #
 # Author: Nathan Woodburn
 
 copy() {
-    if [ $# -eq 0 ]; then
-        echo "No arguments specified."
-        echo "Usage: copy <file>"
-        return 1
-    fi
-
     if tty -s; then
         file="$1"
-        if [ ! -e "$file" ]; then
+        if [ -n "$file" ] && [ ! -e "$file" ]; then
             echo "$file: No such file or directory" >&2
             return 1
         fi
 
         xclip -selection clipboard < "$file"
-
     else
-        file_name="$1"
-        xclip -selection clipboard < "$file_name"
+        xclip -selection clipboard
     fi
 }
 
-# Call the copy function with the provided arguments
+# Call the copy function with the provided arguments or from a pipe
+if [ -t 0 ]; then
     copy "$@"
+else
+    copy
+fi