Linux Shell Script Send Email – As in most programming languages, a function is a way to organize commands for later execution to reduce code repetition. Functions are sometimes called
, etc. In a POSIX shell, function commands are executed in the current shell context. Bash offers the most flexibility anywhere
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A bash compound command is a bash if statement and other conditional structures, created bash loops, or generally a group command using parentheses.
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👉 Recommended advice is to use the former with fn_name() as it is often more portable. Also, the second notation will require the use of parentheses when the function is defined with the function keyword and does not use parentheses () after the function name.
The exit status of a function definition is zero (success) unless another read-only function with the same name already exists or a syntax error occurs.
File with your bash alias. In a shell script, a function can be defined anywhere before it is called for execution, and you can access your function definition using either the source or the dot command. A function is executed when called by name, just like any other shell command.
⚠️ When using brace notation, be sure to separate function and brace content with spaces or newlines, otherwise a syntax error around an unexpected token will be generated. This is for historical reasons, because square brackets are reserved words and can only be recognized as such when separated from a list of commands by white space or another shell metacharacter. Also, when using parentheses, you must end the last command with a semicolon ;, an ampersand &, or a new line.
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. The last example shows how a global variable used in a function is unchanged after being executed in a subfield via parentheses.
Since the function definition calls any compound command, you can directly create a function that uses a loop or conditional structure without using programming commands.
💡 When a shell function is executed, you can access the function name inside the function with the FUNCNAME parameter. Often used when editing scripts in conjunction with the $BASH_LINENO and $BASH_SOURCE bash environment variables.
If you are going to define a function with a name that matches an existing construct or command, you will need to use
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Builtin will first look for the built shell, then the on-disk command found in the $PATH environment variable. You can use
There are two scope variables in bash, global and standard scope. bash settings are default
And found anywhere in your shell script. Although, in a function, you can reduce the scope of the variable by using
Within the work. It refers to how the shell controls the visibility of variables inside functions. How a function sees a parameter depends on whether it is defined within the function or the caller/parent. The advantage of a flexible perimeter is often to reduce the risk of different conflicts in the international perimeter. A
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A variable is a variable defined locally in a function with the same name as the global variable. The local difference eclipses the global difference.
Similar to a shell script, bash functions can take arguments. Arguments are accessed within a function using positional parameter notation such as
, And so on. When a function is executed, the shell script’s positional parameters are temporarily replaced in the function by the function’s arguments and the specified parameter.
A counter loop like the one shown above isn’t necessarily useful, but it does show some interesting possibilities, for example creating a simple one-line bash calculator.
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Status after implementation. By default, the function returns the exit code of the last command executed within the function. It will stop the execution of the function once it is called. You can use
Builtin is limited to 8 significant bits between 0 and 255. Any number greater than 255 will return a null value. If a non-numeric number is used, an error
Builtin should just return an error code related to the execution of the function and not return the actual data.
To return real data, including return strings or large numbers, you can use standard output or a global variable.
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A function is recursive, which means it can call itself. No limit is imposed on the number of repeated calls. Although you can use
Variable to reduce the depth of the function call stack and limit the number of function requests. If you reach
It can be difficult to modify a shell script that depends on standard libraries installed in your script or loaded by you.
In interactive mode. Components with conflicting names can quickly become a problem and substitute for each other. However, there is a way to track, debug, and troubleshoot how your functions are defined and where to find them.
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There are two differences for the shell execution environment between function and caller, both related to how interrupts are handled.
Builtin will set the trace attribute on a specific function only when executed in the source or dot(.) context
⚠️ The bash shell extdebug option will do more than just performance monitoring, see next section. ⚠️ Be careful when enabling trap on return of items as it may change how your script works. Especially when you expect a string from standard function output to be returned as a parameter. The standard trap version will take priority over your normal performance output.
👉 It’s often easier to define your debugging and trapping functions in a separate source file and only call them while debugging using the bash environment variable $BASH_ENV. Find where the bash function is defined.
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In many cases, it can be useful to know where a function is defined so that it can be modified or updated. However, in interactive or non-interactive mode, you cannot easily track specific performances. For bash you will need to enable the
. This option enables a lot of debugging features, including the ability to display the source file name and line number corresponding to the function when using In this quick tip, we’ll see how to use the output of a document as the main body of an email. Linux command line. This is suitable for anyone who wants to run a command and send the results to an email address. Using cron can be a great way to get information about your system or specific programs.
First you need a program that can send email from the Linux command line. I have been using mailx for a few years and recommend it.
Before you begin, you MUST make sure your system is configured to send email. If you are sure it is, you can jump. If you need to configure your system, read “How to send mail via SMTP ISP with Postfix”.
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To test your system’s mail functionality, simply send an email using our newly installed mailx software.
If your system is configured correctly, you will receive a copy of your hosts file in your email.
For more information on sending files, read “Send a File as an Attachment or Email Body from the Command Line”.
Sending the output of a command is different from sending an email to an already existing text file. You cannot redirect easily or you will get a redirect error.
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You will now be able to run a script or run a command and send the result to an email address.
It is very easy to execute a command and send the result by e-mail. It is important to understand how a pipeline operator operates. To learn more, see the links below. Historically, the shell was the original command-line interpreter for Unix-like systems. It has proven to be one of the main features of Unix over the years and has become a new topic in itself. Linux provides a variety of functional shells, including Bash, Zsh, Tcsh, and Ksh. One of the most striking features of these missiles is their configuration. Creating simple yet effective Linux scripts to handle day-to-day tasks is very easy. Moreover, a basic knowledge of this subject will make you an experienced Linux user in no time. Stay tuned for an in-depth introduction to Unix shell scripting.
Most shell scripting done on Linux involves the bash shell. However, experienced users who have specific options set often use other shells such as Zsh and Ksh. We’ll mostly stick to Linux bash scripts in our examples because of their widespread popularity and use. However, our editors have also tried to describe some sample shell scripts that support shells other than bash. As a result, you will acquire a large amount of knowledge between the different shell scripts.
Bash, also known as Bourne Again Shell, is the default command-line interpreter in most Linux distributions these days. It is an enhancement to the original Bourne shell that was first introduced in Unix version 7. Learning bash shell scripts will allow you to understand other shell scripts much faster. So,
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