Process substitution (<() and >()) in Bash Scripting - Mini Project: Build & Apply

Using Process Substitution in Bash Scripts

📖 Scenario: You work with text files and want to compare their contents quickly without creating temporary files.

🎯 Goal: Learn how to use process substitution &lt;() and &gt;() in bash to handle command outputs as files.

📋 What You'll Learn

Create variables holding file names

Use process substitution to compare file contents

Redirect command output using process substitution

Print the comparison result

💡 Why This Matters

🌍 Real World

Process substitution helps you compare or process data streams easily without creating temporary files, saving time and disk space.

💼 Career

Many system administrators and developers use process substitution in bash scripts to automate file comparisons and data processing efficiently.

1

Create two text files

Create two variables called file1 and file2 with values "file1.txt" and "file2.txt" respectively. Then create these files with the following contents: file1.txt contains "apple\nbanana\ncherry" and file2.txt contains "apple\nbanana\norange".

Bash Scripting

# Create variables and files with exact contents
# Your code here

Need a hint?

Use echo -e with newline characters \n to write multiple lines to files.

2

Set up a variable for the diff command

Create a variable called diff_cmd and set it to the string "diff".

Bash Scripting

file1="file1.txt"
file2="file2.txt"
echo -e "apple\nbanana\ncherry" > "$file1"
echo -e "apple\nbanana\norange" > "$file2"
# Create a variable diff_cmd with value "diff"
# Your code here

Need a hint?

Just assign the string "diff" to the variable diff_cmd.

3

Use process substitution to compare files

Use the variable diff_cmd with process substitution to compare the contents of file1 and file2. Write a command using $diff_cmd and process substitution <(cat "$file1") and <(cat "$file2").

Bash Scripting

file1="file1.txt"
file2="file2.txt"
echo -e "apple\nbanana\ncherry" > "$file1"
echo -e "apple\nbanana\norange" > "$file2"
diff_cmd="diff"
# Use process substitution with $diff_cmd to compare file1 and file2
# Your code here

Need a hint?

Use diff_output=$($diff_cmd <(cat "$file1") <(cat "$file2")) to capture the diff output.

4

Print the diff result

Print the variable diff_output using echo.

Bash Scripting

file1="file1.txt"
file2="file2.txt"
echo -e "apple\nbanana\ncherry" > "$file1"
echo -e "apple\nbanana\norange" > "$file2"
diff_cmd="diff"
diff_output=$($diff_cmd <(cat "$file1") <(cat "$file2"))
# Print the diff_output variable
# Your code here

Need a hint?

Use echo "$diff_output" to show the differences.