Here Strings

Here Strings

Here strings are a feature in various programming and scripting languages that allow for the creation of multi-line strings or the redirection of input directly into commands. Here’s a detailed overview:

Definition

A here string is a type of string that allows you to pass a string directly to the standard input (stdin) of a command. It simplifies the process of providing multi-line input without needing to create temporary files or use echo commands.

Syntax

In Bash, here strings are denoted by the <<< operator. The basic syntax is:

command <<< "string"

This passes the specified string as input to the command.

Characteristics

• Multi-line Input: Here strings can handle multi-line text, treating each line as separate input.
• Simplicity: They provide a straightforward way to pass data to commands without additional piping or file management.
• Redirection: Here strings are a form of input redirection, similar to here documents (heredocs), but more concise.

Examples

1. Basic Usage:

   grep "pattern" <<< "This is a test string containing pattern."

   This command searches for “pattern” in the provided string.

2. Multi-line Input:

   tr ' ' '\n' <<< "Line 1 Line 2 Line 3"

   This command replaces spaces with newlines, outputting:

   Line
   1
   Line
   2
   Line
   3
   

3. Using Variables:

   my_var="Hello World"
   echo <<< "$my_var"

   This will output Hello World.

Comparison with Here Documents

While here strings and here documents (heredocs) serve similar purposes, here strings are simpler and more concise. Here documents require a delimiter to indicate the end of the input, whereas here strings do not.

Example of Here Document:

cat << EOF
This is a here document.
It can span multiple lines.
EOF