Description: The ‘error level’ in computing refers to a special variable commonly represented as ‘$?’, which stores the exit status of the last executed command. This value is fundamental for error management in scripts and command line operations across various programming environments. In most systems, an exit status of ‘0’ indicates that the command executed successfully, while any other number represents an error or a specific condition that occurred during execution. This feature allows users and developers to check if a command was successful and, if not, make decisions based on the type of error that occurred. For example, in a script, a conditional structure can be used to check the value of ‘$?’ and execute different actions depending on whether the previous command succeeded or failed. This ability to effectively handle errors is crucial for creating robust and reliable scripts, as it allows developers to anticipate and manage potential issues in command execution.
History: The concept of error levels in operating systems and programming languages dates back to the early days of computing, where there was a need for a way to communicate the success or failure of operations. The use of exit codes became a standard practice as operating systems evolved. Many shells, including popular Unix-like environments, have adopted this convention, allowing scripts and commands to interact more effectively with the operating system.
Uses: The error level is primarily used in scripts to control the flow of execution based on the success or failure of previous commands. This is especially useful in automated tasks, where it is crucial to know if a command executed correctly before proceeding to the next one. Additionally, it is used in script debugging, allowing developers to identify and handle errors more efficiently.
Examples: A practical example of using the error level is as follows: if a command to copy a file is executed and the error level is checked immediately afterward, one can decide whether to proceed with the next operation or display an error message. For example: ‘cp file.txt /destination/path/; if [ $? -ne 0 ]; then echo “Error copying the file”; fi.’
