Here strings (<<<) in Bash Scripting - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to use a here string to pass the word 'hello' to the 'cat' command.

Bash Scripting

cat [1] 'hello'

Drag options to blanks, or click blank then click option'

A<<<

B<

C<<

D>>

Attempts:

3 left

💡 Hint

Common Mistakes

Using '<<' which is for here documents, not here strings.

Using '<' which reads from a file, not a string.

The here string operator in bash is '<<<'. It passes the string on the right as input to the command on the left.

2fill in blank

medium

Complete the code to count the number of words in the string 'one two three' using a here string.

Bash Scripting

wc -w [1] 'one two three'

Drag options to blanks, or click blank then click option'

A>>

B<<

C<

D<<<

Attempts:

3 left

💡 Hint

Common Mistakes

Using '<' which expects a filename, causing an error.

Using '<<' which expects a delimiter for a here document.

Using '<<<' passes the string as input to 'wc -w' which counts words.

3fill in blank

hard

Fix the error in the code to correctly use a here string to grep the word 'apple' in the string 'apple banana'.

Bash Scripting

grep apple [1] 'apple banana'

Drag options to blanks, or click blank then click option'

A<<

B<<<

C<

D>>

Attempts:

3 left

💡 Hint

Common Mistakes

Using '<' which expects a file, causing an error.

Using '<<' which is for here documents, not here strings.

The correct operator for passing a string as input is '<<<'.

4fill in blank

hard

Fill all blanks to create a here string that converts 'hello world' to uppercase using 'tr'.

Bash Scripting

tr [1] [2] [3] 'hello world'

Drag options to blanks, or click blank then click option'

A'[:lower:]'

B'[:upper:]'

C<<<

D<<

Attempts:

3 left

💡 Hint

Common Mistakes

Using '<<' instead of '<<<' for here string.

Swapping the character sets in 'tr'.

The 'tr' command translates characters from the first set to the second. The here string operator '<<<' passes the string as input.

5fill in blank

hard

Fill both blanks to create a dictionary of word lengths for words longer than 3 letters using a here string and Python.

Bash Scripting

python3 <<< "words = 'apple banana cat dog'.split()\nlengths = [1]: len([2]) for [2] in words if len({{BLANK_2}) > 3}\nprint(lengths)"

Drag options to blanks, or click blank then click option'

A{word

Bword

C}

Dwords

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'words' instead of 'word' as the loop variable.

Missing closing brace in the dictionary comprehension.

The dictionary comprehension syntax is {word: len(word) for word in words if len(word) > 3}. The here string passes the Python code as input.

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