Edit Text File Bash Script Example' title='Edit Text File Bash Script Example' />The easiest way is to use sed or perl sed i e sabcXYZg tmpfile.Which will invoke sed to do an inplace edit due to the i option.How to Write a Batch File with ExamplesCommunity Tested.Two Methods Writing a Batch File.Sample Batch File.Community Q AA batch file contains a series of DOS commands, and is commonly written to automate frequently performed tasks.Instead of typing the same commands over and over, you can simply double click the batch file.Writing a batch file is easier than it looks the difficult part is making sure that everything happens in the right order.Well made batch files can save you a lot of time over the long run, especially if you deal in repetitive tasks.Filetofolder script.Bobo February 21, 2009.This didnt work for me.Running Vista Home Premium.Wouldve been nice, but it ended up.Bash Script Step By Step, You will love it.Today we are going to talk about bash scripting or shell scripting and how to write your first bash script.Actually, they are called shell scripts in general, but we are going to call them bash scripts because we are going to use bash among the other Linux shells.There are zsh, tcsh, ksh and other shells.In the previous posts, we saw how to use the bash shell and how to use Linux commands.The concept of a bash script is to run a series of Commands to get your job done.To run multiple commands in a single step from the shell, you can type them on one line and separate them with semicolons.Actually, this is a bash script The pwd command runs first, displaying the current working directory then the whoami command runs to show the currently logged in users.You can run multiple commands as much as you wish, but with a limit.You can determine your max args using this command.ARGMAXWell, What about putting the commands into a file, and when we need to run these commands we run that file only. 147 Windows 7 Themes Uj Online here. This is called a bash script.First, make a new file using the touch command.At the beginning of any bash script, we should define which shell we will use because there are many shells on Linux, bash shell is one of them.Bash Script Shebang.The first line you type when writing a bash script is the followed by the shell you will use.If you use the pound sign in front of any line in your bash script, this line will be commented which means it will not be processed, but, the above line is a special case.This line defines what shell we will use, which is bash shell in our case.The shell commands are entered one per line like this.This is a comment.This is a commentpwdwhoami.You can type multiple commands on the same line but you must separate them with semicolons, but it is preferable to write commands on separate lines, this will make it simpler to read later.Set Script Permission.After writing your bash script, save the file.Now, set that file to be executable, otherwise, it will give you permissions denied.You can review how to set permissions using chmod command.Then try run it by just typing it in the shell.And Yes, it is executed.Print Messages. As we know from other posts, printing text is done by echo command.Edit our file and type this.The current directory is.The user logged in is.The current directory is pwdechoThe user logged in is whoami.Look at the output Perfect Now we can run commands and display text using echo command.If you dont know echo command or how to edit a file I recommend you to view previous articles about basic Linux commands.Using Variables. Variables allow you to store information to use it in your script.You can define 2 types of variables in your bash script Environment variables.User variables. Environment Variables.Sometimes you need to interact with system variables, you can do this by using environment variables.Home for the current user is HOMEbinbash display user homeechoHome for the current user is HOMENotice that we put the HOME system variable between double quotations, and it prints the home variable correctly.What if we want to print the dollar sign itself I have 1 in my pocketBecause variable 1 doesnt exist, it wont work.So how to overcome that You can use the escape character which is the backslash before the dollar sign like this echoI have 1 in my pocketNow it works User Variables.Also, you can set and use your custom variables in the script.You can call user variables in the same way like this.User variables. echo person is a good boy, he is in grade gradebinbash User variablesgrade5personAdamechoperson is a good boy, he is in grade grade.Command Substitution.You can extract information from the result of a command using command substitution.You can perform command substitution with one of the following methods The backtick character.The format. Make sure when you type backtick character, it is not the single quotation mark.You must enclose the command with two backticks like this mydirpwdOr the other way mydirpwdSo the script could be like this.The output of the command will be stored in mydir variable.Math calculation.You can perform basic math calculations using 2 2 format.Just that easy. if then statement.You bash scripts will need conditional statements.Like if the value is smaller than 1.You can imagine any logic you want.The most basic structure of if then statement is like this if commandthendo somethingfiand here is an example.It works. fibinbashifwhoamithenechoIt worksfi.Since the whoami command will return my user so the condition will return true and it will print the message.Lets dig deeper and use other commands we know.Maybe searching for a specific user in the users file etcpasswd and if a record exists, tell me that in a message.No such a user user.No such a user userfi.We use the grep command to search for the user in etcpasswd file.You can check our tutorial about the grep command.If the user exists, the bash script will print the message.What if the user doesnt exist The script will exit the execution without telling us that the user doesnt exist.OK, lets improve the script more.Statement. The if then else statement takes the following structure if commandthendo somethingelsedo another thingfi.If the first command runs and returns zero which means success, it will not hit the commands after the else statement, otherwise, if the if statement returns non zero which means the statement condition fails, in this case, the shell will hit the commands after else statement.User. if grep user etcpasswd.The user user Exists.The user user doesnt exist.UserifgrepuseretcpasswdthenechoThe user user ExistselseechoThe user user doesnt existfi.We are doing good till now, keep moving.Now, what if we need more else statements.Well, that is easy, we can achieve that by nesting if statements like this if condition.If the first command return zero means success, it will execute the commands after it, else if the second command return zero, it will execute the commands after it, else if none of these return zero, it will execute the last commands only.User. if grep user etcpasswd.The user user Exists.The user doesnt exist.UserifgrepuseretcpasswdthenechoThe user user ExistseliflshomethenechoThe user doesnt existfi.You can imagine any scenario here, maybe if the user doesnt exist, create a user using the useradd command or do anything else.Numeric Comparisons.You can perform a numeric comparison between two numeric values using numeric comparison checks like this number.Checks if number.Checks if number.Checks if number.Checks if number.Checks if number.Checks if number.As an example, we will try one of them and the rest is the same.Note that the comparison statement is in square brackets as shown.The num is greater than 1.String Comparisons.You can compare strings with one of the following ways string.Checks if string.Checks if string.Checks if string.Checks if string.Checks if string.Checks if string.We can apply string comparison on our example.USER. echo The user user is the current logged in user.USERthenechoThe user user is the current logged in userfi.One tricky note about the greater than and less than for string comparisons, they MUST be escaped with the backslash because if you use the greater than symbol only, it shows wrong results.So you should do it like that.It runs but it gives this warning.To fix it, wrap the vals with a double quotation, forcing it to stay as one string like this.One important note about greater than and less than for string comparisons.Check the following example to understand the difference.Likegeeksv. 2likegeeksifv.Likegeeks. The test condition considers the lowercase letters bigger than capital letters.Unlike the sort command which does the opposite.The test condition is based on the ASCII order, while the sort command is based on the numbering orders from the system settings.File Comparisons.You can compare and check for files using the following operators d myfile Checks if its a folder.Checks if the file is available.Checks if its a file.Checks if its readable.Checks if myfile is newer than myfile.Checks if myfile is older than myfile.
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