Echoing to stderr in Bash
The default error message variable for built-in Bash scripts is called stderr. It is also called standard error and is the default output device for errors.
Sometimes we have to redirect the error to an output channel. The Linux environment identifies each file object and its description, called FD.
It is a positive integer value identifying an open file session. For stderr, the file descriptor has the value 2.
In this article, we will learn about stderr and its functions. Also, we will look at some examples that will make the topic easier to understand.
Echoing to stderr in Bash
The command stderr is mainly used to keep a recode of the errors during the execution of any command. The general syntax of the command is:
Your command here 2>error.log
In the example syntax shared above, you can find a symbol 2> and a file called error.log. Now 2> represents the value of FILE DESCRIPTOR, which represents the identity of stderr.
In our case, the value of FILE DESCRIPTOR is 2. Now the file name we provide is for the log file generated during the command execution.
You can also echo stderr messages using the following syntax format.
Your command here >&2 echo "error"
Let's look at an example to simplify the topic. Suppose we have created an error command and want to echo the error message to the output.
Our example code will now look like this:
echo $( 3 + 2 )) >&2 echo "error"
In the code shared above, we have made a mistake intentionally to understand how it works. We have removed one of the brackets here, so this might be a mistake.
After that, we use echo to display the error. Running the above code will display the output as shown below.
./example.sh: line 1: syntax error near unexpected token `)'
./example.sh: line 1: `echo $( 3 + 2 )) >&2 echo "error" '
Now we correct the code as follows and run the command again.
echo $(( 3 + 2 )) >&2 "No error has been found."
After running the code, you will get the output as shown below.
5 No error has been found.
All the codes used in this article are written in Bash. It will only work in Linux Shell environment.
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