Here strings (<<<) in Bash Scripting - Step-by-Step Execution

Concept Flow - Here strings (<<<)

Start script

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Use <<< to send string

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Command reads string as input

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Command processes input

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Output result

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End script

The script uses <<< to send a string directly as input to a command, which then processes it and outputs the result.

Execution Sample

Bash Scripting

grep 'hello' <<< 'hello world'
echo $?

This code searches for 'hello' in the string 'hello world' using a here string and prints the exit status.

Execution Table

Step	Action	Command Input	Command Output	Exit Status
1	Send 'hello world' to grep via here string	'hello world'	hello world	0
2	Print exit status of grep		0
3	End of script

💡 grep finds 'hello' in the input string, so exit status is 0 (success).

Variable Tracker

Variable	Start	After Step 1	After Step 2	Final
Command Input		'hello world'	'hello world'	'hello world'
Exit Status		0	0	0

Key Moments - 2 Insights

Why does grep get the string without using a file?

Because the here string (<<<) sends the string directly as input to grep, so no file is needed. See execution_table step 1.

What does the exit status 0 mean after grep runs?

Exit status 0 means grep found the pattern in the input. See execution_table step 2 where exit status is printed.

Visual Quiz - 3 Questions

Look at the execution table, what is the command input to grep at step 1?

A 'hello'

B Empty string

C 'hello world'

D 'world hello'

💡 Hint

Check the 'Command Input' column in execution_table row for step 1.

At which step is the exit status of grep printed?

A Step 2

B Step 1

C Step 3

D It is never printed

💡 Hint

Look at the 'Action' column in execution_table to find when exit status is printed.

If the string did not contain 'hello', what would the exit status be?

A 0

B 1

C 2

D No exit status

💡 Hint

Exit status 1 means grep did not find the pattern; see common grep exit codes.

Concept Snapshot

Here strings (<<<) send a string as input to a command.
Syntax: command <<< 'string'
The command reads the string as if from a file.
Useful for quick input without files.
Exit status shows if command succeeded.

Full Transcript

This example shows how to use a here string (<<<) in bash scripting. The here string sends the string 'hello world' directly as input to the grep command. Grep searches for the word 'hello' in this input. Since 'hello' is found, grep outputs the matching line and sets the exit status to 0, meaning success. Then the script prints the exit status. This method avoids creating a file for input and is a quick way to provide input to commands.