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validate does not accept substrings (remove the -x option to grep if you want that). Reference: Advanced Bash Script guide. Add the following code: #!/bin/bash Check if strings are not equal in Bash Instead of checking the quality, let’s do the opposite and check the inequality. You want the -n test ("true if the length of the given string is non-zero"), which is the opposite of the -z test ("true if the length of the given string is zero"). How to check if a string contains a substring in Bash (14) Compatible answer. This is a synonym for the test command/builtin. So as you see now I have used curly braces {} to make sure the separator is not considered part of the variable, now let's check the output from the script: ~]# ./eg_1.sh Hello_World This is the one of the most important thing you should always remember when working with bash string concatenation. Sample code to exercise the function: Bash If statement syntax is I tested on MS Windows 7 using bash 4.3.46 (works fine) and bash 3.1.17 (didn't work) The LHS of the =~ should be in quotes. The -p test is something completely different ("true if the given file exists and is a named pipe"). Above, PHONE_TYPE="SPACE TEL" would match too. This information is available to you in an interactive bash … does - bash string not contains . Now you can use any other special character here to combine both the strings. Note: not using quotes will cause issues when words contain spaces, etc. Bash 4+ examples. Please note that you need at least bash 4 for this use of =~ It doesn't work in bash 3. You can look in the Bash man page in the section called "Parameter Expansion" for information about ${var//string} and ${var#string} and in the section called "Pattern Matching" for [^[:digit:]]` (which is also covered in man 7 regex). Please note that the following is bash specific syntax and it will not work with BourneShell: if grep -q "$user2" /etc/passwd; then echo "User does exist!!" You can use (!=) operator to check when both strings are not equal. Check If Two Strings are Not Equal (!=) Bash also provides the negation operator to use “if not equal” condition in bash scripts. In my bash script I'm trying to print a line if a certain string does not exist in a file. However, [[is bash’s improvement to the [command. When comparing strings in Bash you can use the following operators: string1 = string2 and string1 == string2 - The equality operator returns true if the operands are equal. Here are some examples Bash 4+: Example 1, check for 'yes' in string (case insensitive): if [[ "${str,,}" == *"yes"* ]] ;then Example 2, check for 'yes' in string (case insensitive): The [and [[evaluate conditional expression. validate interprets its argument as a fixed string, not a regular expression (remove the -F option to grep if you want that). You need to pass the -z or -n option to the test command or to the if command or use conditional expression.This page shows how to find out if a bash shell variable has NULL value or not using the test command. Example – if -z (to check if string has zero length) Example – if -s (to check if file size is greater than zero) Example – if -n (to check if string length is not zero) Example – if -f (to check if file exists and is a regular file) Syntax of Bash If. Bash check if a string contains a substring . Let’s create a new test.sh script as shown below: nano test.sh. If the string on it somehow represents a regex (like [0-9] for example), there is a higher chance to trigger a "match". Always quote in Bash IMO. You can quickly test for null or empty variables in a Bash shell script. Bash also provides the negation operator so that you can easily use “if not equal” condition in shell scripts. Equal ” condition in shell scripts substrings ( remove the -x option to grep if want... Shell scripts check if a string contains a substring in bash ( 14 ) Compatible answer s a! Script I 'm trying to print a line if a string contains a substring in (. A new test.sh script as shown below: nano test.sh you can use (! = operator... Also provides the negation operator so that you can use any other special character here to combine the. A new test.sh script as shown below: nano test.sh does not exist a. Something completely different ( `` true if the given file exists and is a named pipe '' ) -q $... 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