While creating a bash script, you might encounter a situation where you need to find whether a file exists or not to perform some action with it. In this example script we will collect multiple input arguments using getopts. Check File Existence using shorter forms. bash test.sh. However, [[is bash’s improvement to the [command. The name stands for Global Regular Expression Print. You can use the test command to check if file exists and what type is it. Furthermore, the bash manual warns that this sort of pattern matching is slow if the string which should be matched is long. The [and [[evaluate conditional expression. The script will prompt you to enter a number. ; The statements that follow the then statement can be any valid UNIX command, any executable user program, any executable shell script, or any shell statement with the exception of fi. For example: #!/bin/bash echo “How old are you?” read age It doesn't call your check_log function at all.. Change it to this: if check_log; By the way, the function could be more simply written as: Here is a list of all comparison operators:-eq – equal to-ne – not equal to-lt – less than-le – less than or equal to-gt – greater than-ge – greater than or equal to. And as per the previous comments, when using bash or ksh, it's recommended to use ((..)) for numerical tests, and [[..]] for string/file tests and complex expressions. if [ check_log ]; When you use square brackets you're invoking the test command. Again if we execute the same script with some other flag: # bash single_arg.sh -m Invalid option: -m. Example-2: Collect multiple input arguments. Of course, too many nested levels can be unwieldy as well, so two conditions per test seems like a good balance to me. Please note that the following is bash specific syntax and it will not work with BourneShell: In this tutorial, we will show you how to check if file exists in the Linux-based operating systems. The variable is greater than 10. if..else Statement # The Bash if..else statement takes the following form: You can also use the elif statement to test for any number of conditions. Grep is a powerful utility available by default on UNIX-based systems. If, for example, you enter 15, the test command will evaluate to true because 15 is greater than 10, and the echo command inside the then clause will be executed. It's equivalent to if test check_log which is shorthand for if test -n check_log, which in turn means "if "check_log" is not an empty string". # bash single_arg.sh -h showing usage! Bash check if a string contains a substring . Avoid using the old [..] test unless you specifically need POSIX-style portability. You can grep multiple strings in … By using the grep command, you can customize how the tool searches for a pattern or multiple patterns in this case. Need Multiple checks inside if condition in a bash shell script Hi, I need to perform the untar and rm operation if the file found is a .tar and does not have test.tar or hello.tar as the file names. In some cases, you may be interested in checking if a file exists or not directly in your Bash shell. Basic Syntax of Test Command While creating a bash script, it is commonly helpful to test if file exists before attempting to perform some action with it.. Please note that the solution shown below might be bash-only, because I have no clue about the differences between bash and other shells. ./single_arg.sh -h --> shows usage. This is a synonym for the test command/builtin. 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