Capture Groups with Quantifiers In the same vein, if that first capture group on the left gets read multiple times by the regex because of a star or plus quantifier, as in ([A-Z]_)+, it never becomes Group 2. For an introduction to Bash regular expressions, see our Bash regular expressions for beginners with examples article instead. Bash substring with regular expression, In a bash script, I´d like to extract a variable string from a given string. Method 3. I read line by line through the data, and for that, i have some data i have to extract from that line. grep , expr , sed and awk are some of them.Bash also have =~ operator which is named as RE-match operator.In this tutorial we will look =~ operator and use cases.More information about regex command cna be found in the following tutorials. 8 thoughts on “How To Assign Output of a Linux Command to a Variable” Michael Schwager. Linux bash provides a lot of commands and features for Regular Expressions or regex. A regular expression can match part of the line; if you want to match the whole line, put ^ at the beginning of the regex and $ at the end. These hold information Bash can readily access, such as your username, locale, the number of commands your history file can hold, your default editor, and lots more. Use the regular expression match operator =~ if you want to have an extended regular expression on the right-hand side. I'm trying to match multiple alphanumeric values (this number could vary) from a string and save them to a bash capture group array. i need a string checked for an Regex and the Match should be returned into a variable. If you're trying to count the number of files in a directory that have names matching the globbing pattern stored in your shell variable named (confusingly) file_name, you could try something … Note that you don't grep a folder (usually called a directory in UNIX and Linux environments). Execute the shell script, and the variable is successfully converted into array and the strings can be iterated separately # /tmp/split-string.sh My array: string1 string2 string3 Number of elements in the array: 3 Method 4: Bash split string into array using tr I mean, i´d like to extract the string file.txt from the string: This is the file.txt this regex matching on the grep command fails all the time, even if the line contains F08R16 pattern. All this have to be done in a bash. January 30, 2017 at 9:37 am You missed process substitution. I checked that line for an value, if that is true, i need the regexp match as result back, to get stored in a value. Environment Variables. Or, if you grep for username tom, you’ll also get tomcat. Using the power of regular expressions, one can parse and transform textual based documents and strings. Install Linux from USB Device or Boot into Live Mode Using Unetbootin and dd Command. It will also match viveki, vivek25, etc. That’s a good bash tip, but that grep may give you some unexpected output. For good and for bad, for all times eternal, Group 2 is assigned to the second capture group from the left of the pattern as you read the regex. use bash regular expressions to capture the variable name (due to greedy matching, this matches variable names from right to left use variable indirection to get the variable value remove the matched varname from the input string to avoid infinite loop (this destroys the original string, back it … This article is for advanced users, who are already familiar with basic regular expressions in Bash. The grep utility searches for text in the contents of text files (not directories on most systems). Bash uses environment variables to define and record the properties of the environment it creates when it launches. 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