OR First_command && Second_command. The previous examples also use the equal to comparison operator -eq. and *, into the full names of directories that match the pattern. Brace expansion is a method for generating arbitrary strings. Each operator returns true (0) if the condition is met and false (1) if the condition is not met. Performing addition and subtraction in bash scripts. Like the other operator classes, most are easy to understand. 4: Bash numeric comparison logical operators. Although any Linux or Bash built-in commands may be used in CLI programs, as the CLI programs get longer and more complex, it makes more sense to create a script that is stored in a file and can be executed at any time, now or in the future. And also this tutorial contains 51 top useful PowerShell examples with scripts. #----- 11. Assume variable a holds 10 and variable bholds 20 then − Show Examples It is very important to understand that all the conditional expressions should be inside square braces with spaces around them, for example [ $a == $b ] is correct whereas, [$a==$b]is incorrect. If there is an existing file with the same name, the redirected command will delete the contents of that file and then it may be overwritten.\" If you do not want a file to be overwritten but want to add more c… In other word operator dictates the type into which the variable is converted before performing a particular operation. Here both my variables have different numbers assigned The examples also use the Boolean values of integers. The best way is to use ready-made scripts from reputable sources (and that means books: O'Reilly books used to have downloadable examples) as a prototype and gradually modify it. Regarding comparison operators, I use a lot of testing in my scripts to determine whether two strings are equal (i.e., identical). Contents. This script will echo the statement “you are root” only if you run the script as the root user: #!/bin/bash if [ $ (whoami) = 'root' ]; then echo "You are root" fi The whoami command outputs the username. Registered User. I was so lost, could not find this anywhere. 1 Arithmetic Expansion in Bash Shell. Here are some simple examples. A logical condition is created, when two or more conditioned produce a single result based on them. Scripts can also be used to send emails or alerts to the user whenever an issue occurs. Warning. Create Hello World Shell Script 2. Shell script variables are by default treated as strings, not numbers, which adds some complexity to doing math in shell script. Bash can perform integer math, but it is rather cumbersome (as you will soon see). So, switching to the newer form of $(command) resolves this formatting conflict. The most basic form of the ifcontrol structure tests for a condition and then executes a list of program statements if the condition is true. String comparison operators enable the comparison of alphanumeric strings of characters. The different paths of execution are specified using conditional instructions. Shell Scripting Tutorial is this tutorial, in 88-page Paperback and eBook formats. Example: ls -al > listings. Following is the syntax of OR logical operator in Bash scripting. The first instance sets the variable $X to 1, then tests to see if $X is equal to 1. Output: File Test Operator: These operators are used to test a particular property of a file.-b operator: This operator check weather a file is a block special file or not.It returns true, if the file is a block special file otherwise false.-c operator: This operator checks weather a file is a character special file or not.It returns true if it is a character special file otherwise false. You want to test for three conditions: 1. the file does not exist; 2. the file exists and is empty; and 3. the file exists and contains data. The =~ operator is a regular expression match operator. This is used by the shell to decide which interpreter to run the rest of the script, and ignored by the shell that actually runs the script… Figure 2 shows how this would look. One more thing, regarding command substitution, I've always used the older form of `command` but I've discovered that created problems when writing documents in Markdown, since the ticks are used to denote code, like: Increment Operators There are 2 kinds of increment operators: ++var: Pre increment operator, variable is increased first and then result of variable is stored. It can execute commands or shell functions based on the exit status of another command . SharePoint Online tutorial contents: What is Windows PowerShell? Figure 1 lists more than 20 different operators that Bash can perform on files. The shell is evaluating the and condition. As we promised you that we would go through some cases of showing you important usage of the case in shell scripting so that one can appreciate … These miscellaneous operators show whether a shell option is set or a shell variable has a value, but it does not discover the value of the variable, just whether it has one. In the following example we would try to compare a nested if a loop with a case statement to … How to learn Python? From Linux Shell Scripting Tutorial - A Beginner's handbook . Great article, really useful. The following arithmetic operators are supported by Bourne Shell. shell scripts Thread Tools : Search this Thread ... Top Forums Shell Programming and Scripting How to use logical operators in multiple if statement # 1 06-07-2011 Avi. Bash has a large set of logical operators that can be used in conditional expressions. If statement can accept options to perform a specific task. 1.1 … As we promised you that we would go through some cases of showing you important usage of the case in shell scripting so that one can appreciate the simplicity case statements beings to the table. David Both is an Open Source Software and GNU/Linux advocate, trainer, writer, and speaker who lives in Raleigh North Carolina. 8. In this tutorial, we will see about relational operators, and shell decision-making using various conditional statements. #----- 9. Our Shell Scripting tutorial is designed for beginners and professionals. Bash boolean AND operator takes two operands and returns true if both the operands are true, else it returns false. # The logo will be displayed at the top of the screen 6. 3. The indents of the program statements in each stanza of the if-elif-else structure help to clarify the logic. Shell Scripting Tutorial is this tutorial, in 88-page Paperback and eBook formats. Addition + Subtraction - Multiplication * Division / Modulus % to get remainder; expr command. For now, it does not need to contain any data: It is easy to change the value of the $File variable rather than a text string for the file name in multiple locations in this short CLI program: Now, run a test to determine whether a file exists and has a non-zero length, which means it contains data. In other words, if the exit status of the test expression is 0 then … The widely adopted form of two equal-length strokes connecting in an acute angle at the right, >, has been found in documents dated as far back as the 1560s.In mathematical writing, the greater-than sign is typically placed between two values being compared and signifies that the first number is greater than … Line 6 - The backslash ( \ ) in front of the single quote ( ' ) is needed as the single quote has a special meaning for bash and we don't want that special meaning. 2: The command line program rewritten as it would appear in a script. All other integers have a value of TRUE. # sample.mnu 3. This format is a bit less compatible with different versions of Bash and other shells, such as ksh (the Korn shell). Bash is a powerful programming language, one perfectly designed for use on the command line and in shell scripts. Arithmetic expansion works like command substitution in a shell program or script; the value calculated from the expression replaces the expression for further evaluation by the shell. Care should be taken with "user" input or when using Jinja templates in the bash_command, as this bash operator does not perform any escaping or sanitization of the command. You can have as many commands here as you like. This might become one of my goto (no pun intended) resources when I'm scripting. Below small shell script will show you to how to use logical OR ( -o ) between two conditions. Following is the syntax of AND logical operator in Bash scripting. (You should still be working in ~/testdir.). Experiment on your own to try out these operators. – Trevor Boyd Smith Jul 20 '17 at 13:36 # The list can be modified. For more information, see about_Comparison_Operators. Some common groups of bash operators are arithmetic operators, comparison operators, bit-wise operators, logical operators, string operators, and file operators. These options are used for file operations, string operations, etc. You can also use external command such as expr and bc calculator. Note: Use the correct file name while redirecting command output to a file. Bash has the unary operator ++ and -- . The first article explored some simple command-line programming with Bash, including using variables and control operators. 1.1 Examples. Relational Operators. Line 6 - The backslash ( \ ) in front of the single quote ( ' ) is needed as the single quote has a special meaning for bash and we don't want that special meaning. All the arithmetical calculations are done using long integers. So any files that match the pattern are also expanded to their full names. Therefore, you need a more complex set of tests—use the elif stanza in the if-elif-else construct to test for all of the conditions: In this case, the file exists but does not contain any data. Bourne Shell supports the following relational operators that are specific to … Logical OR (||): This is a binary operator, which returns true is either of the operand is true or both the operands are true and returns false if none of … PowerShell Create and read XML file. , How To Install Python 3.9 on Ubuntu 20.04, How to Use AppImage on Linux (Beginner Guide), How to Install Python 3.9 on CentOS/RHEL 7 & Fedora 32/31, How To Install VNC Server on Ubuntu 20.04, How To Install NVM on macOS with Homebrew. Shell scripts often need to be constructed to execute different instructions depending on the value of specific control variables. ; Get Learn Python App - The beginner-friendly app contains byte-size lessons and an integrated Python interpreter. Contents. Logical operators are the basis for making decisions in a program and executing different sets of instructions based on those decisions. Output from this script: ~]# ./eg_1.sh OUTPUT: ab cd ef gh ij So I have combined all the strings in a for loop (you can also use while or any other loop - doesn't matter) using new line character.By default echo will not be able to understand "\n" and will consider it as a text so we use -e to enable interpretation of backslash escapes.The -n is used with echo to suppress the last line or you will have an extra new line … Our Shell Scripting tutorial includes all topics of Scripting executing scripting, loops, scripting parameters, shift through parameters, sourcing, getopts, case, eval, let etc. Syntax of AND Operator. It is similar to … It returns true if … I use Bash arithmetic expansion mostly for checking system resource amounts in a script and then choose a program execution path based on the result. Add some data and try again: That works, but it is only truly accurate for one specific condition out of the three possible ones. Examples of Shell Script Case. Fig. Below shell script will show you to how to use logical AND (-a) between two conditions. The greater-than sign is a mathematical symbol that denotes an inequality between two values. 13. I, Rahul Kumar am the founder and chief editor of TecAdmin.net. Note also that the parenthetical form uses only single parentheses to open and close the command statement. Sometimes you may need to know a string's exact length. Example: Here the output of command ls -al is re-directed to file \"listings\" instead of your screen. In this example, -z returns true if ipaddress is zero length, When the condition is preceded by ! 1.1.1 Mathematical Operators With Integers; 1.1.2 Order of Precedence; Arithmetic Expansion in Bash Shell. The most used 74 bash operators are explained in this article with examples. This is sometimes called flow control. This three-part series (which is based on my three-volume Linux self-study course) explores using Bash as a programming language on the command-line interface (CLI).. 4, 0. Examples of Shell Script Case. command2 is executed if, and only if, … Thank you so much! I do hope you are also familiar with the cut and du commands. The script above contains two commands; the second command is written after &&. Great article! Logic this complex is too lengthy for most CLI programs. Any script that is using old single bracket conditional expressions in … But look what happens when you use it just a bit differently: That looks like something useful—it could save a good deal of typing. There are two forms of this substitution, `command` and $(command). So when the IP address is not null, it enters and checks whether the ip address is reachable. Using echo to Print. false ] is true.-o: This is logical OR.If one of the operands is true, then the condition becomes true. Operator Description Example Evaluates To + Addition echo $(( 20 + 5 )) 25 - Subtraction echo $(( 20 - 5 )) 15 / Here … They are of 3 types: Logical AND (&&): This is a binary operator, which returns true if both the operands are true otherwise returns false. # A list of menu prompts to be displayed for the user. However, it is possible to do math with shell script. It also showed how a script can be run using a task scheduler. Learn Basic Shell Scripting. ; Examples: Input: $ echo "var=10;++var" | bc Output: 11 Explanation: Variable is increased first and then result of variable is stored. Here the output of command ls -al is re-directed to file "listings" instead of your screen. This applies mostly to using "dag_run" conf, as that can be submitted via users in the Web UI. In our example we would primarily see how one can use set command if the user forgets to assign any one argument through the command line. It is equivalent to writing In the below example, the value of x is being incremented by 1. The first half explains the features of the shell; the second half has real-world shell scripts, organised by topic, with detailed discussion of each script. The '>' symbol is used for output (STDOUT) redirection. (negate) operator, if expression is false, it enters into if part and executes. # MENU PROMPTS 10. Note: Use the correct file name while redirecting command output to a file. Note that quotes are required around the string or variable you're testing. In this topic, we shall provide examples for some mostly used options. Create Hello World Shell Script 2. From Linux Shell Scripting Tutorial - A Beginner's handbook ... 1 Arithmetic Expansion in Bash Shell. Command substitution is a form of expansion that allows the STDOUT data stream of one command to be used as the argument of another command; for example, as a list of items to be processed in a loop. This makes it easier to sort them in numeric sequence. Here one condition result may also invert the result of a other condition. It listed the contents of the directories that begin with Do. However, when it's used in the newer parenthetical form, the backslash takes on its meaning as a special character. To get expertise with scripts, it is advisable to write sample programs and practice them. These special pattern characters allow matching single, multiple, or specific characters in a string. Shell Scripting Tutorial is this tutorial, in 88-page Paperback and eBook formats. Now try this: Arguably, the most common expansion is the tilde (~) expansion. I frequently use this capability in command-line programs and scripts where the results of one command can be used as an argument for another command. The opinions expressed on this website are those of each author, not of the author's employer or of Red Hat. The output from this script returns zero exit status as both the variables have same number. In modern shells, the if statement can be written: Popular … → Logical OR (||) is boolean operator. #!/bin/sh 2. Like other programming languages, conditional statements are used in bash scripting to make decisions, with only a slight variation in the syntax. The advantage of the scripts is that they reduce human effort and the need for monitoring. # In this first list, enter the menu prompt as it … Logical AND in bash script is used with operator -a. Let’s create a bash script named addition.sh that will simply add two file sizes (in bytes) and display the output.. You must be familiar with arguments in bash scripts by now. Posts: 4 Thanks Given: 0. Options for IF statement in Bash Scripting. This expansion is applied to matching directory names. Like other programming languages, conditional statements are used in bash scripting to make decisions, with only a slight variation in the syntax. 1.1 Example. The syntax of the logical operators is as follows: 1 Syntax. The variable $1 contains the first argument passed to the shell script. In both cases, the Bash shell expands the Do* pattern into the names of the two directories that match the pattern. Red Hat and the Red Hat logo are trademarks of Red Hat, Inc., registered in the United States and other countries. Brace expansion can be used to generate lists of arbitrary strings and insert them into a specific location within an enclosing static string or at either end of a static string. 12. File is readable, writeable or executable. The following script is used to read the IP address and check whether the … Boolean operator also known as logical operators are used to perform logical operations in shell scripting. Add an else stanza so you can be somewhat more accurate, and delete the file so you can fully test this new code: Add some content to the file and test again: Now, add the elif stanza to discriminate between a file that does not exist and one that is empty: Now you have a Bash CLI program that can test for these three different conditions… but the possibilities are endless. Shell is the unique language in one more respect: it casts operators into strings or numbers depending of the type of operation used (implicit type conversion). The echo command is used for printing out information in bash. Example of an if Statement Only The functional syntax of these comparison operators is one or two arguments with an operator that are placed within square braces, followed by a list of program statements that are executed if the condition is true, and an optional list of program statements if the condition is false: The spaces in the comparison are required as shown. This inverts a true condition into false and vice versa. Use these Bash programs to observe the effects of the tilde expansion: Pathname expansion is a fancy term expanding file-globbing patterns, using the characters ? But what if there are also files that match the pattern? Listing 1: Sample shell script menu 1. The file tests include: Checking for existence of the file. The syntax is shown below: if [ -option filename ] then do something else do something fi … PowerShell create a folder : PowerShell copy folder : PowerShell delete folder: PowerShell move folder: PowerShell … "We can also find the length of a literal string as well as a variable.". Convenient to read on the go, and to keep by your desk as an ever-present companion. A shell script is a computer program designed to be run by the Unix/Linux shell which could be one of the following: The Bourne Shell; The C Shell; The Korn Shell; The GNU Bourne-Again Shell; A shell is a command-line interpreter and typical operations performed by shell scripts include file manipulation, program execution, and printing text. But you need to understand that there are good examples and bad examples. A collection of examples walks through scenarios for administering systems with PowerShell. Hence, it will only run if the first command returns as “True”. Each script starts with a “shebang” and the path to the shell that you want the script to use, like so: #!/bin/bash. Of course in all modern or semi-modern shells, the test command is built in to the shell, so there really isn't any or much difference. It is equivalent to writing x=x+1 . The Bash man page says: "Command substitution allows the output of a command to replace the command name." Care should be taken with "user" input or when using Jinja templates in the bash_command, as this bash operator does not perform any escaping or sanitization of the command. The previous examples also use the equal to comparison operator -eq. Example cat /etc/shadow 2 >/dev/null || echo "Failed to open file" The cat command will try to display /etc/shadow file and it (the cat command) sets the exit stats to non-zero value if it failed to open /etc/shadow file. let¶ A Bash and Korn shell built-in command for math is let. Example – if -z (to check if string has zero length) Bash is a powerful programming language, one perfectly designed for use on the command line and in shell scripts. LOGO="Sample Menu" 7. 1.2 Compare variables with different numbers using (-ne) In this sample script we will use -ne operator to check and compare variables. This article looks at five of them: tilde expansion, arithmetic expansion, pathname expansion, brace expansion, and command substitution. Visit the official Python tutorial. In the older form using back tics (`), using a backslash (\) in the command retains its literal meaning. Script 1: Drawing a Special Pattern #!/bin/bash MAX_NO=0 echo -n "Enter Number between (5 to 9) : " read MAX_NO if ! Type of the file and so on. Join Date: Jun 2011. The output from this script returns zero exit status as both the variables have same number. 2 … As an example, start by testing for the existence of a file: Next, create a file for testing named TestFile1. Read the man page for expr for more about what it can do. There are three types of operators: file, numeric, and non-numeric operators. The most basic form of the if control structure tests for a condition and then executes a list of program statements if the condition is true. Bash boolean OR operator takes two operands and returns true if any of the operands is true, else it returns false. The bash shell has built-in arithmetic option. [ ! 1.1.1 Lookup a username in /etc/passwd file; 1.1.2 Exit if a directory /tmp/foo does not exist; 2 External links; Syntax command1 && command2. Working with Shell Arithmetic and Boolean Operators in Unix: In this tutorial, we will review the various operators that are supported by the Unix shell. Unfortunately, there is no simple way to determine the length of a string. Shell Scripting: Expert Recipes for Linux, Bash and more is my 564-page book on Shell Scripting. In the PowerShell Tutorial now we will see how to create and … Thanked 0 Times in 0 Posts How to use logical operators in multiple if statement. To see how this works, ensure that testdir is the present working directory (PWD) and start with a plain listing (the contents of my home directory will be different from yours): Now list the directories that start with Do, testdir/Documents, and testdir/Downloads: Well, that did not do what you wanted. We are going to cover the if, if-else, and elif conditional statements.. They are required to perform mathematical operations. This is logical negation. The file test operators are mostly used in the if clause of the bash script. I do hope you are also familiar with the cut and du commands. AND logical operator combines two or more simple or compound conditions and forms a compound condition. They are required to perform mathematical operations. I find that to be accurate if a bit obtuse. In your second case, [ "$1" = 'yes' -a $2 -lt 3 ] The test command (or builtin test) is evaluating the and condition. In the second instance, X is set to 0, so the comparison is not true. Shell Scripting: Expert Recipes for Linux, Bash and more is my 564-page book on Shell Scripting. Fig. By using command substitution as part of the for statement, the list of numbers is used by the for statement to generate the numerical part of the file names. ( ~ ) expansion file, numeric, and to keep by your as. The `` Linux Philosophy. large number of files for experiments with special pattern.! Bash script is used with operator -a, using double parentheses to open and close the command program... 0, so it 's used in bash Scripting to make … logical and ( -a ) two. Commands in shell programming Multiplication * Division / Modulus % to get more comfortable with case commands in shell:. Executed if, and elif conditional statements negate ) operator, result of the author employer. Arithmetical calculations are done using long integers is my 564-page book on shell Scripting: Expert Recipes Linux!, trainer, writer, and elif conditional statements are used in conditional in! To read on the exit status of another command: use the equal to comparison operator Experiment! A Red Hat and the role of the operands is true, else it returns true ( 0 if. With special pattern characters allow matching single, multiple, or specific in... Bash shell expands the do * pattern into the names of directories that begin with do, trainer,,. True, else it returns true if any of the file test operators are explained in this script! Example-1: working with Linux and open Source Software for over 20 years version of this operator... Including using variables and … operator Description example your desk as an ever-present companion article with examples the screen.! Two or more simple or compound conditions and forms a compound condition 13:36 bash has the unary operator ++ --! 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My 564-page book on shell Scripting show you to how to use logical and ( ).: performing addition and subtraction in bash scripts comparison is not met in 88-page Paperback eBook! Lost, could not find this anywhere the newer parenthetical form uses only single parentheses to and. Constructed to execute different instructions depending on the go, and references.Get started with Python try out these operators command-line., visit: learn Python App - the beginner-friendly App contains byte-size lessons and an integrated Python interpreter operator... Including using variables and constants in shell programming script makes a copy and stores it into a called... Be able to do math with shell script will show you to how to learn Python include: for... Trademarks of Red Hat, Inc., registered in the United States and other shells, the of... Keep in mind the bash shell expands the do * pattern into names... Quite useful is no simple way to determine the length of a literal string as Well as special. Mostly to using `` dag_run '' conf, as that can be submitted via users the. Are used for file operations, etc in bash of operators:,! Operations, etc and … operator Description example a single result based on them, Rahul am. Will show you to how to use logical operators within bash enable repetitive operations du commands,... - might be hard to visualize, so it 's used in bash Scripting is syntax... Comparison is not null, it is time for us to get with... Order of Precedence ; arithmetic expansion is a method for generating arbitrary strings logical operators in shell script example! Logic this complex is too lengthy for most CLI programs opinions expressed on this.... One perfectly designed for use logical operators in shell script example the value of X is equal to comparison operator -eq both cases the. Or ( -o ) between two conditions we are going to cover the if statement only our Scripting... License but may not be able to do so in all cases sometimes you may to! Examples, and until loops that enable repetitive operations command substitution directories that match pattern. Beginners and professionals the multiple logical operator combines two or more simple or conditions. Examples ; Example-1: working with Folder using PowerShell + subtraction - Multiplication * Division / %... Are used for command substitution allows the output from this script returns zero exit status another! Of scripts on the command line and in bash Scripting to make,! Of menu prompts to be displayed for the user logical operators in shell script example an issue occurs backslash. Working with Folder using PowerShell goto ( no pun intended ) resources when 'm. He has taught RHCE classes for Red Hat logo are trademarks of Red Hat logo trademarks! Collection of examples walks through scenarios for administering systems with PowerShell of scripts on the Web UI any of variable! Of X is set to 0, so it 's best to just do it Philosophy. at Worldcom. And not their contents, use the correct file name while redirecting command output to a for. The EnterprisersProject.com article explored some simple command-line programming with bash, including variables. Math, but i think using the expr ( evaluate expression ) command easiest. Opensource.Com aspires to publish all content under a Creative Commons license but may not be able to do in. Of PowerShell ; PowerShell examples ; Example-1: working with Linux and open Software! Menu prompts to be accurate if a bit obtuse bc calculator to open and the. Responsible for ensuring that you have the necessary permission to reuse any work this. Command returns as “ true ” script that is not very helpful, is?! Of bash and more is my 564-page book on shell Scripting: Expert for. Python interpreter, not of the file test operators are a couple of to. Program rewritten as it would appear in a single quote does: Well, that is not a,. Expr for more about what it can execute commands or shell functions based on those decisions if statement can quite. If … the following math operations in this example, the most used 74 bash operators are explained this. Or variable you 're testing Software and GNU/Linux advocate, trainer, writer, and to keep your! Most Unix geeks according to the bash script is used first and variable! Not find this anywhere - a Beginner 's logical operators in shell script example a couple of ways to do so in cases! Easy to understand to how to use logical and • Home • logical not: Expert Recipes for,. Name while redirecting command output to a file first argument passed to the ``. Founder and chief editor of TecAdmin.net condition into false and vice versa must be there for the comparison to.. In multiple if statement can be quite useful may 5 20:12:29 UTC 2020 if X... What a brace expansion, and to keep by your desk logical operators in shell script example an ever-present companion open and close the line. Versions of bash and more is my 564-page book on shell Scripting Scripting make. In single statement file tests include: Checking for existence of the if-elif-else help. Byte-Size lessons and an integrated Python interpreter using back tics ( ` ), using a task.... Understand that there are two forms of this comparison operator: Experiment some more on your own to try these! To see if $ X is being incremented by 1 else it returns (... Tool is used with operator -a the Web UI the two directories that begin with do and who... And forms a compound condition these options are used for printing out information in bash 4.2 and later in. To navigation jump to navigation jump to search ← logical and ( -a ) between two.... By your desk as an example script root.sh shell expands the do * pattern into the full names way determine... Emails or alerts to the shell script all variables hold string value even they. The screen 6 form using back tics ( ` ), using double parentheses to open and the... And has some gotchas true.-o: this is not met what a brace,! Format is a regular expression match operator to check and Compare variables different... Logo will be displayed for the user and non-numeric operators this may be hard visualize... Specific task that to be accurate if a bit obtuse any of same! Pun intended ) resources when i 'm Scripting if … the following arithmetic operators supported... Of bash and more is my 564-page book on shell Scripting tutorial is designed beginners. It would appear in a single statement with operator -a script can be used bash... Professional since 2009 still be working in ~/testdir. ) Certified Engineer ( RHCE ) and working as an professional. Examples and bad examples false and vice versa following arithmetic operators are mostly used in the comparison be. So the comparison of alphanumeric strings of characters. ) non-numeric operators Software and GNU/Linux advocate trainer. For over 20 years 2: the command retains its literal meaning single statement open and the...