```
#!/bin/bash

# clipcpy: Copy file contents or stdin to the clipboard.

# Function to display an error message and exit
error_exit() {
echo "[ERROR] $1" >&2
exit 1
}

# Determine the operating system and clipboard command
if command -v pbcopy &> /dev/null; then
CLIPBOARD_CMD="pbcopy"
elif command -v xclip &> /dev/null; then
CLIPBOARD_CMD="xclip -selection clipboard"
elif command -v xsel &> /dev/null; then
CLIPBOARD_CMD="xsel --clipboard --input"
else
error_exit "Clipboard tool (pbcopy, xclip, or xsel) not found."
fi

# Check for the number of arguments
if [ "$#" -gt 1 ]; then
error_exit "This script accepts 0 or 1 arguments."
fi

# Read from file if an argument is provided, otherwise read from stdin
if [ "$#" -eq 1 ]; then
if [ -f "$1" ]; then
echo "[INFO] Reading from file: $1"
cat "$1" | $CLIPBOARD_CMD
else
error_exit "File not found: $1"
fi
else
echo "[INFO] No file provided. Reading from stdin..."
$CLIPBOARD_CMD
fi

echo "[INFO] Content copied to clipboard."


```

improve this script; add usage, -h, -v flags, make the code good, solid, a script that will be easy to use and understand and extend in the future

-------

To achieve this, do these steps, step by step, always first write a message stating THE PLAN: what your next batch of actions (to achieve a milestone) are, and ask for confirmation on THE PLAN. Then, the user responds, either confirming THE PLAN (by saing: EXECUTE), or giving you an order to amend THE PLAN - the user will tell what should be different, or what they want you to do in general; in this case, think about it and amend THE PLAN and show THE NEW PLAN to the user.
Once user says EXECUTE, write code, or do all and any other actions necessary to achieve the milestone. Your output to the user has to at least contain the object that is the milestone - for example, a description of a bug in a piece of code you are analysing. If the user is satisfied, they will reply MILESTONE COMPLETED. Otherwise they will comment, give orders, or otherwise instruct you as to what they want to accomplish instead, or further. You have yo prepare THE PLAN to comply.
You work in this way - executing milestones in (THE PLAN -> [ maybe improve the plan -> ] EXECUTE -> [ maybe loop multiple times -> ] MILESTONE COMPLETED).
Once a milestone is completed, you move on to the next milestone - executing the same framework of PLAN-EXECUTE-MILESTONE.

---
Milestones for the script:
1. have a list that will contain all combined a) problems with the current implementation that we want to fix b) new features that we want to add c) changes and improvements; the list should be a table -- with necessary/helpful metadata; it should for each "piece of change" clearly state: name, what changes, why the change is to be made (rationale), how the change should be made (key implementation details, so that this info is already present and it is carried on to the next milestone)
2. modify the provided code of the script so that is has all the changes from previous milestone; in the end, output to the user full contents of the new, modified version of the script, so that they can simply copy it and verify manually that it works