Linux echo all env

How to print / echo environment variables?

The expansion $NAME to empty string is done by the shell earlier, before running echo , so at the time the NAME variable is passed to the echo command’s environment, the expansion is already done (to null string).

To get the same result in one command:

Note that only the printenv -based command preserves the semantics of the OP’s command: defining NAME as a command-scoped environment variable, which only the invoked command and its child processes see, but no subsequent shell commands. The other commands do something very different: they define NAME as an until-the-current-shell-exits shell-only variable, which all subsequent shell commands see, but no external utilities.

To bring the existing answers together with an important clarification:

As stated, the problem with NAME=sam echo «$NAME» is that $NAME gets expanded by the current shell before assignment NAME=sam takes effect.

Solutions that preserve the original semantics (of the (ineffective) solution attempt NAME=sam echo «$NAME» ):

Use either eval [1] (as in the question itself), or printenv (as added by Aaron McDaid to heemayl’s answer), or bash -c (from Ljm Dullaart’s answer), in descending order of efficiency:

NAME=sam eval 'echo "$NAME"' # use `eval` only if you fully control the command string NAME=sam printenv NAME NAME=sam bash -c 'echo "$NAME"' 

printenv is not a POSIX utility, but it is available on both Linux and macOS/BSD.

What this style of invocation ( = cmd . ) does is to define NAME :

• as an environment variable
• that is only defined for the command being invoked.

In other words: NAME only exists for the command (child process) being invoked, and has no effect on the current shell (if no variable named NAME existed before, there will be none after; a preexisting NAME variable remains unchanged).

POSIX defines the rules for this kind of invocation in its Command Search and Execution chapter.

The following solutions work very differently (quoted from heemayl’s answer):

NAME=sam; echo "$NAME" NAME=sam && echo "$NAME" 

While they produce the same output, they instead define:

• a shell variable NAME (only) rather than an environment variable
  • if echo were a command that relied on environment variable NAME , it wouldn’t be defined (or potentially defined differently from earlier).

  Note that every environment variable is also exposed as a shell variable, but the inverse is not true: shell variables are only visible to the current shell and its subshells, but not to child processes, such as external utilities and (non-sourced) scripts (unless shell variables are designated as environment variables (too) with export or declare -x ).

  [1] Technically, bash is in violation of POSIX here (as is zsh ): Since eval is a special shell built-in, the preceding NAME=sam assignment should cause the the variable $NAME to remain in scope after the command finishes, but that’s not what happens.
  However, when you run bash in POSIX compatibility mode, it is compliant.
  dash and ksh are always compliant.
  The exact rules are complicated, and some aspects are left up to the implementations to decide; again, see Command Search and Execution.
  Also, the usual disclaimer applies: Use eval only on input you fully control or implicitly trust.

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  How to print / echo environment variables in Bash?

  In Bash scripting, environment variables are important elements that hold specific information about the system and its environment. Printing or echoing the value of environment variables can be useful for debugging or displaying information about the system. In this tutorial, we will show you several methods for printing or echoing the value of environment variables in a Bash script.

  Method 1: Using the «echo» Command

  To print or echo environment variables in Bash using the «echo» command, you can use the following syntax:

  Where «VARIABLE_NAME» is the name of the environment variable you want to print. Here are some examples:

  echo $HOME echo $PATH echo $MY_VAR

  You can also print the values of multiple environment variables in a single command by separating them with spaces:

  To print the names and values of all environment variables, you can use the following command:

  This will print a list of all environment variables and their values in the format «VARIABLE_NAME=value».

  You can also use the «echo» command to print text and environment variable values together:

  echo "My home directory is: $HOME"

  In this example, the value of the «HOME» environment variable is printed along with a message.

  That’s it! Using the «echo» command is a simple and effective way to print or echo environment variables in Bash.

  Method 2: Using the «$» Syntax

  To print environment variables in Bash using the «$» syntax, you can use the «echo» command followed by the variable name enclosed in curly braces. Here are some examples:

  echo "The home directory is: $HOME>"

  This will print the value of the «HOME» environment variable.

  echo "The user is: $USER> and the shell is: $SHELL>"

  This will print the values of the «USER» and «SHELL» environment variables.

  This will print «Hello, John!» by using the value of the «name» variable in the string.

  num1=10 num2=5 echo "The sum of $ and $ is $((num1+num2))."

  This will print «The sum of 10 and 5 is 15.» by using the values of the «num1» and «num2» variables in the calculation.

  This will list the contents of the «Documents» directory in the user’s home directory by using the value of the «HOME» variable in the «dir» variable and then passing it to the «ls» command.

  In summary, using the «$» syntax is a simple and effective way to print environment variables in Bash. You can use it to print single or multiple variables, use variables in strings, calculations, or commands.

  Method 3: Using the «printf» Command

  To print or echo environment variables in Bash using the «printf» command, you can use the following code:

  Here, «VARIABLE_NAME» is the name of the environment variable that you want to print. The «%s\n» format specifier is used to print the string value of the variable followed by a newline character.

  You can also use the «printf» command to print multiple environment variables at once, like this:

  printf "%s=%s\n" "VARIABLE1" "$VARIABLE1" "VARIABLE2" "$VARIABLE2"

  In this example, the «%s=%s\n» format specifier is used to print the name and value of two environment variables, «VARIABLE1» and «VARIABLE2».

  If you want to print all environment variables, you can use the following code:

  Here, the «env» command is used to list all environment variables, and the «$()» syntax is used to capture the output of the command and pass it as an argument to the «printf» command.

  Finally, if you want to format the output of the environment variables, you can use the «printf» command with custom format specifiers, like this:

  printf "Variable 1: %-20s\nVariable 2: %s\n" "$VARIABLE1" "$VARIABLE2"

  In this example, the «%-20s» format specifier is used to left-align the value of «VARIABLE1» with a minimum width of 20 characters, and the «%s» specifier is used to print the value of «VARIABLE2».

  Method 4: Using the «declare» Command

  To print or echo environment variables in Bash using the «declare» command, follow these steps:

  1. Open your terminal or command prompt.
  2. Type the following command to print all environment variables:

  This command will display all environment variables with their values and attributes.

  Replace «VARIABLE_NAME» with the name of the environment variable you want to print.

  Replace «VARIABLE_NAME» with the name of the environment variable you want to print.

  This command will display all environment variables with their values sorted alphabetically.

  These are some examples of how to print or echo environment variables in Bash using the «declare» command. You can use these commands to manipulate and work with environment variables in your Bash scripts.

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  Bash Print All Environment Variables and Values

  

  Your shell compiles multiple types of information while interacting with the server from the shell session. It provides information about the shell behavior and its access to the resources. Configuration settings contain some of these settings, and user input determines others.

  In this way, the shell keeps track of all settings and information to maintain the environment. Shells build an environment each time they start a session that contains variables that define a system’s properties. So, if you want to know the methods to bash print all environment variables and values, then read this blog to get a brief on it.

  Bash Print All Environment Variables and Values

  By using the commands env or printenv, we can see all of our environment’s variables. So here is the following command and its output:

  

  

  Both printenv and env produce similar results. They differ only in how they carry out certain tasks. When you use printenv, for example, you can see the values of specific variables using the below command:

  

  According to what we learned above, child processes usually inherit the environment variables from parent tasks, allowing you to easily override or add variables to them.

  Printenv displays that several environmental variables have been set without our input through our system files and processes.

  You can use the set command for this. Without any other parameters, typing set will get us a list of environmental variables, all shell variables, shell functions, and local variables:

  

  Most of the time, this list is very long. So, you can use the following command for the lesser output:

  

  It is probably not necessary to learn about all of the Bash functions, for instance.

  To clean up the output, we can specify to operate in POSIX mode, which will not print shell functions. So that it doesn’t change any current environment, we can run this in a subshell:

  

  There are some environmental variables and shell variables that must be listed here.

  The output of these commands will not match the output of env or printenv, so we cannot obtain only shell variables using these comparisons, but using these commands will give us a partial list:

  

  While this is true, a few environmental variables may still be present since printenv and env don’t quote strings as they do.

  In your session, you will still see the environment variables and shell variables you set.

  There are many uses for these variables. These technologies offer an alternative to writing changes to files to set persistent session values.

  Common Linux Variables

  We display values of shell variables in Linux using the printf/echo commands:

  Conclusion

  So, it was the brief information on the bash print of all environment variables and values. We have included the best possible details to view the environment variable through the Linux terminal. Make sure you visit our official website to know more about Linux.

  About the author

  Prateek Jangid

  A passionate Linux user for personal and professional reasons, always exploring what is new in the world of Linux and sharing with my readers.

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