While creating a bash script, it is commonly helpful to test if file exists before attempting to perform some action with it.This is a job for the test command, that allows to check if file exists and what type is it.As only the check is done – the test command sets the exit code to 0 ( TRUE) or 1 ( FALSE), whenever the test succeeded or not.Also the test command has a logical “not” operator which allows to get the TRUE answer when it needs to test if file does not exist.Cool Tip: Create a clever bash script! Make it do more tests! Check easily whether a string exists in a file! Bash Shell: Test If File ExistsRun one of the below commands to check whether a file exists: $ test -f FILENAME– or – $ -f FILENAME Test if the file /etc/passwd exist ( TRUE): $ test -f /etc/passwd$ echo $?0$ -f /etc/passwd $ echo $?0Test if the file /etc/bebebe exist ( FALSE): $ test -f /etc/bebebe$ echo $?1$ -f /etc/bebebe $ echo $?1Test if the file /etc/bebebe does not exist ( TRUE): $ test! -f /etc/bebebe$ echo $?0$ ! -f /etc/bebebe $ echo $?0 If File Exists, Then. It goes without saying that we don’t just check whether a file exists without a reason.We usually test if a file exists to perform some action depending on the result of the test.Maybe if file doesn’t exist – there is no sens to move forward and it is required to break the script or whatever.In the examples below, lets print corresponding messages depending on the results of the test command.Cool Tip: The CASE statement is the simplest form of the IF-THEN-ELSE statement!

1. How To Write A Shell Script Unix

If you have many ELIF elements – it is better to use the CASE!Test if the file /etc/passwd exists and print a message if it is TRUE: $ if -f '/etc/passwd' ; then echo 'The file exists'; fiThe file existsTest if the file /etc/bebebe does not exist and print a message if it is TRUE: $ if ! -f '/etc/bebebe' ; then echo 'The file does not exist'; fiThe file does not existTest if the file exists and print a corresponding message in the each case: $ -f '/etc/passwd' && echo 'The file exists' echo 'The file does not exist'The file exists$ -f '/etc/bebebe' && echo 'The file exists' echo 'The file does not exist'The file does not exist Bash Script: Test If File Exists. Lets create a bash script, that will check whether a passed as an argument file exists or not, by printing a corresponding message.Create an empty checkfile.sh file with the touch checkfile.sh command.Make it executable with chmod +x checkfile.sh.Open the checkfile.sh with a text editor and put the following code: #!/bin/bashFILE=$1if -f $FILE ; thenecho 'The file '$FILE' exists.' Elseecho 'The file '$FILE' in not found.' FiCool Tip: A good bash script prints usage and exits if arguments are not provided!

It is very simple to configure!Save and execute the script as follows: $./checkfile.sh /etc/bebebeThe file '/etc/bebebe' is not found.$./script.sh /etc/passwdThe file '/etc/passwd' exists.

What You Will Learn:.Advanced Shell Scripting in UnixUnix includes commands for:. Testing various conditions associated with specified files. Testing various conditions associated with specified strings. Performing file read/write operations.ArraysArrays are used to store a series of values in an indexed list.

How To Write A Shell Script Unix

Items in an array are stored and retrieved using an index. Note that Arrays are not supported by the original Bourne Shell, but are supported by bash and other newer shells. File Test OperatorsShell scripts often need to check various properties of files as a part of the control flow. Unix provides a number of options for this purpose.

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