Standard Error

"Standard Error", usually called "stderr", is a data stream just like standard output, but is intended to be used for error messages.

It's a separate stream so that you can redirect it to a different place if need be, but by default, it prints to your terminal just like stdout.

Redirecting Streams

You can redirect stdout and stderr to different places using the > and 2> operators. > redirects stdout, and 2> redirects stderr.

Redirect stdout to a File

echo "Hello world" > hello.txt
cat hello.txt
# Hello world

Redirect stderr to a File

cat doesnotexist.txt 2> error.txt
cat error.txt
# cat: doesnotexist.txt: No such file or directory

In this example, cat is used to intentionally generate an error message (since the file doesn't exist), which is then redirected to error.txt.

Assignment

There is a process_transactions.sh script in the worldbanc/private/bin directory.

It accepts a path to a CSV file containing transactions data as a positional argument (or CLI argument)
It prints modern transactions (after the year 2000) to stdout, and old transactions (before the year 2000) to stderr

Run the script:
- Use the path to the 2020.csv file in the worldbanc/private/transactions directory as an argument.
- Be sure to redirect stderr to a temporary file called /tmp/worldbanc.log.

If you're missing 2020.csv, you made a mistake in a previous step! Ensure the files in transactions match the files in transactions/backups. If not, make a copy. Alternatively, manually copy the file contents from GitHub.

cat the /tmp/worldbanc.log file to see the old transactions.

Paste those transactions into the text field and submit your answer.

The temporary directory (/tmp) exists by default on all Unix-like systems in your root directory. Files there are deleted by your system routinely. It's a great place to store temporary files that you don't need to keep around.