Here strings (<<<) in Bash Scripting - Mini Project: Build & Apply

Using Here Strings (<<<) in Bash Scripting

📖 Scenario: You are writing a small bash script to process a short text input without creating a separate file. You want to use a simple way to send a string directly to a command.

🎯 Goal: Learn how to use the here string operator &lt;&lt;&lt; to pass a string as input to a command in bash.

📋 What You'll Learn

Create a variable with a short text string

Use a here string to send the variable content to the wc -w command to count words

Store the word count in a variable

Print the word count

💡 Why This Matters

🌍 Real World

Here strings let you quickly send small pieces of text to commands without creating files. This is useful in scripts that process dynamic or short inputs.

💼 Career

Many automation and scripting tasks require passing data to commands efficiently. Knowing here strings helps write cleaner, faster bash scripts.

1

Create a variable with a text string

Create a variable called text and set it to the string "Hello world from bash scripting" exactly.

Bash Scripting

# Create a variable called text with the exact string
# Your code here

Hint

Use = to assign the string to the variable text. Enclose the string in double quotes.

2

Use a here string to count words

Create a variable called word_count and set it to the output of the command wc -w using a here string with the variable text as input.

Bash Scripting

text="Hello world from bash scripting"
# Use a here string to count words in text and save to word_count
# Your code here

Hint

Use $(command) to capture command output. Use wc -w <<< "$text" to count words from the variable.

3

Trim whitespace from word count

Update the word_count assignment to remove any leading or trailing whitespace from the output using tr -d ' '.

Bash Scripting

text="Hello world from bash scripting"
word_count=$(wc -w <<< "$text")
# Remove whitespace from word_count output
# Your code here

Hint

Pipe the output of wc -w to tr -d ' ' to delete spaces.

4

Print the word count

Write a echo command to print the text Word count: followed by the value of the variable word_count.

Bash Scripting

text="Hello world from bash scripting"
word_count=$(wc -w <<< "$text" | tr -d ' ')
# Print the word count
# Your code here

Hint

Use echo "Word count: $word_count" to display the result.

Practice

1. What does the here string operator <<< do in bash scripting?

easy

A. Redirects output to a file

B. Starts a multiline comment

C. Sends a short string as input to a command

D. Creates a new shell process

Solution

1. Step 1: Understand the purpose of here strings

   Here strings use <<< to send a short string directly as input to a command without needing a file.

2. Step 2: Compare with other redirections

   Unlike output redirection or comments, here strings provide input data inline.

3. Final Answer:

   Sends a short string as input to a command -> Option C

4. Quick Check:

   Here strings = send input string [OK]

Hint: Here strings send input text directly to commands [OK]

Common Mistakes:

• Confusing input with output redirection
• Thinking it creates files
• Mixing with multiline comments

2. Which of the following is the correct syntax to use a here string to send the text "hello world" to the cat command?

easy

A. cat <<<"hello world"

B. cat << hello

C. cat < hello

D. cat <<< hello world

Solution

1. Step 1: Identify correct here string syntax

   The here string operator is <<< followed by a quoted string to preserve spaces or special characters.

2. Step 2: Check each option

   cat <<< hello world misses quotes, which can cause word splitting. cat << hello uses here document syntax. cat < hello is input redirection from a file. cat <<<"hello world" correctly uses cat <<<"hello world".

3. Final Answer:

   cat <<<"hello world" -> Option A

4. Quick Check:

   Quotes needed with here strings = cat <<<"hello world" [OK]

Hint: Use <<< with quotes for strings containing spaces [OK]

Common Mistakes:

• Omitting quotes causing errors
• Using << instead of <<<
• Confusing input redirection with here strings

3. What is the output of the following command?

grep 'world' <<< "hello world"

medium

A. "

B. world

C. hello

D. hello world

Solution

1. Step 1: Understand grep with here string input

   The here string sends "hello world" as input to grep. Grep searches for lines containing 'world'.

2. Step 2: Determine grep output

   The entire line "hello world" contains 'world', so grep outputs the full line.

3. Final Answer:

   hello world -> Option D

4. Quick Check:

   grep outputs matching lines = hello world [OK]

Hint: grep prints full matching lines from input [OK]

Common Mistakes:

• Expecting only the matched word
• Confusing grep output with cut or awk
• Thinking here string changes grep behavior

4. Identify the error in this script snippet:

read name <<

medium

A. No error, script runs fine

B. read command cannot use here strings

C. Missing quotes around John in here string

D. Incorrect use of echo syntax

Solution

1. Step 1: Analyze the here string usage

   The here string operator works with read and does not require quotes for simple alphanumeric strings like John.

2. Step 2: Check the given snippet

   read name << correctly sets name=John (even with literal \n if present), and echo "Name is $name" outputs correctly. No syntax or runtime errors.

3. Final Answer:

   No error, script runs fine -> Option A

4. Quick Check:

   Here strings + read works without quotes for simple input [OK]

Hint: Here strings with read work without quotes for simple input [OK]

Common Mistakes:

• Assuming read can't use here strings
• Thinking quotes are always required
• Misunderstanding echo syntax

5. You want to count how many times the word "error" appears in a log line stored in a variable line. Which command correctly uses a here string to do this?

hard

A. grep 'error' < $line | wc -l

B. grep -o 'error' <<< "$line" | wc -l

C. echo $line | grep -c 'error'

D. wc -l <<< "$line" | grep 'error'

Solution

1. Step 1: Understand the goal

   We want to count occurrences of 'error' in the variable line.

2. Step 2: Analyze each option

   grep -o 'error' <<< "$line" | wc -l uses here string to send $line to grep with -o (outputs each match on a new line), then counts lines with wc -l, correctly counting occurrences.
   grep 'error' < $line | wc -l tries to redirect input from a file named by $line, which is wrong.
   echo $line | grep -c 'error' echoes line and uses grep -c, which counts matching lines, not occurrences.
   wc -l <<< "$line" | grep 'error' pipes wc -l output to grep, which is incorrect usage.

3. Final Answer:

   grep -o 'error' <<< "$line" | wc -l -> Option B

4. Quick Check:

   Use grep -o with here string to count matches [OK]

Hint: Use grep -o with <<< and wc -l to count matches [OK]

Common Mistakes:

• Using grep -c which counts lines, not matches
• Redirecting input from variable as file
• Misordering pipes causing wrong output