Using the cut Command
Specifying the character index isn't the only way to extract a substring. You can also use the -d and -f flags to extract a string by specifying characters to split on. The -d flag lets you specify the delimiter to split on while -f lets you choose which substring of the split to choose.
Bash provides an option to extract the information from a string itself. You can extract the digits or a given string using several methods.
Example 3: To Extract a Single Character
Under Linux, the awk command has quite a few useful functions. One of them, which is called substr, can be used to select a substring from the input. Here is its syntax: substr(s, a, b) : it returns b number of chars from string s, starting at position a.
Another option to determine whether a specified substring occurs within a string is to use the regex operator =~ . When this operator is used, the right string is considered as a regular expression. The period followed by an asterisk . * matches zero or more occurrences any character except a newline character.
`sed` command is another option to remove leading and trailing space or character from the string data. The following commands will remove the spaces from the variable, $myVar using `sed` command. Use sed 's/^ *//g', to remove the leading white spaces. There is another way to remove whitespaces using `sed` command.
A Shell script usually needs to test if a command succeeds or a condition is met. In Bash, this test can be done with a Bash if statement.
What are the Bash Conditional Expressions?
|-a file||True if file exists.|
|-b file||True if file exists and is a block special file.|
To replace content in a file, you must search for the particular file string. The 'sed' command is used to replace any string in a file using a bash script. This command can be used in various ways to replace the content of a file in bash. The 'awk' command can also be used to replace the string in a file.
Awk is an excellent tool for building UNIX/Linux shell scripts. AWK is a programming language that is designed for processing text-based data, either in files or data streams, or using shell pipes.
Awk in Shell Scripts – Passing Shell Variables TO Awk.
|Category||List of Unix and Linux commands|
Since version 3 (circa 2004), bash has a built-in regular expression comparison operator, represented by =~. ... A regular expression is some sequence of characters that represents a pattern. For example, the [0-9] in the example above will match any single digit where [A-Z] would match any capital letter.
$ expands to the process ID of the shell. So, you can see the PID of the current shell with echo $$ . See the Special Paramaters section of man bash for more details.
Any of the following syntaxes can be followed to count the length of string.
Steps to write and execute a script