Bash String Manipulation

You can extract a portion of a string using the ${string:start:length} syntax, where start is the starting index (0-based) and length is the number of characters to extract:

String Length

To find the length of a string, use the ${#string} syntax:

Find and Replace

You can find and replace substrings within a string using the ${string/find/replace} syntax:

To replace all occurrences, use the following:

Uppercase and Lowercase Conversion:

To convert a string to uppercase, use ${string^^} . To convert to lowercase, use ${string,,}:

Regular Expressions

Regular expressions (regex) are powerful patterns for matching and manipulating text. They allow you to define complex search patterns. For example, using grep to find lines containing numbers:

Here, [0-9]+ is a regular expression matching one or more digits.

sed can use regular expressions for text substitution:

Command Substitution

Command substitution allows embedding the output of a command within a string or assigning it to a variable.

Here, date +"%Y-%m-%d" is a command whose output is assigned to the variable currentDate.

Arrays

Arrays in Bash allow storing and manipulating multiple strings. Example:

In this example, fruits is an array with three elements. ${fruits[1]} accesses the second element (index 1). The loop iterates through all elements in the array.

Substring Replacement

Replace specific substrings within a string using ${string/substring/replacement}.

Pattern Matching

Utilize wildcard characters (* and ?) for pattern matching and manipulation.

Trimming Whitespace

Remove leading and trailing whitespace using parameter expansion.

String Comparison

Compare strings using conditional constructs like [[ $string1 == $string2 ]] or [[ $string1 != $string2 ]].

String Slicing

Extract a range of characters from a string using parameter expansion: ${string:start:length}.

String Splitting

Split a string into an array using IFS (Internal Field Separator) and read into an array variable.

String to Array Conversion

Convert a string to an array using read or by iterating over characters.

Quoting

Handle strings with special characters using single or double quotes for proper quoting and escaping.

String Comparison for Sorting

Compare strings numerically or lexicographically to facilitate sorting operations.

String Length Check

Evaluate if a string is empty or not using conditional constructs like [[ -z $string ]] or [[ -n $string ]].

Points to Remember:

1. Quote your strings: Enclose strings in quotes to prevent unexpected interpretation by the shell. Single quotes (') preserve special characters, while double quotes (") allow variable expansion.
2. Error handling: Check for errors and handle them smoothly to avoid script crashes. Use conditional statements and exit codes effectively.

Conclusion

String manipulation in Bash involves operations like concatenation, substring extraction, length calculation, find and replace, and case conversion. Bash provides built-in features for effective string handling, enabling tasks such as pattern matching with regular expressions and utilizing command substitution, while arrays offer a way to store and manipulate multiple strings.