Report generation script in Bash Scripting - Step-by-Step Execution

Concept Flow - Report generation script

Start Script

↓

Define Variables

↓

Collect Data

↓

Process Data

↓

Generate Report File

↓

Display/Save Report

↓

End Script

The script starts by setting variables, collects and processes data, then generates and saves a report before ending.

Execution Sample

Bash Scripting

#!/bin/bash
name="Sales Report"
date=$(date +"%Y-%m-%d")
echo "$name - $date" > report.txt
echo "Total Sales: 100" >> report.txt
cat report.txt

This script creates a simple sales report file with a title, date, and total sales, then shows the report.

Execution Table

Step	Action	Variable Values	Output	Notes
1	Set name variable	name='Sales Report'		Prepare report title
2	Get current date	date='2024-06-15' (example)		Store date in variable
3	Write title and date to report.txt	report.txt contains 'Sales Report - 2024-06-15'		Create report file with header
4	Append total sales line	report.txt now has two lines		Add sales data
5	Display report.txt content		Sales Report - 2024-06-15 Total Sales: 100	Show final report
6	Script ends			All steps complete

💡 Script ends after displaying the report content.

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	After Step 4	Final
name	undefined	Sales Report	Sales Report	Sales Report	Sales Report	Sales Report
date	undefined	undefined	2024-06-15	2024-06-15	2024-06-15	2024-06-15
report.txt	file does not exist	file does not exist	contains header line	contains header line	contains header + sales line	contains header + sales line

Key Moments - 2 Insights

Why do we use > in the echo command at step 3 and >> at step 4?

At step 3, > creates or overwrites the report file with the header line. At step 4, >> appends the sales line without deleting the existing content, as shown in the execution_table rows 3 and 4.

How does the date command store the current date in the variable?

The date command runs and its output is captured by $(...) and assigned to the variable 'date' at step 2, so the variable holds the current date string, as seen in variable_tracker after step 2.

Visual Quiz - 3 Questions

Look at the execution table, what is the content of report.txt after step 3?

A "Total Sales: 100"

B "Sales Report - 2024-06-15"

C "Sales Report - 2024-06-15\nTotal Sales: 100"

D Empty file

💡 Hint

Check the 'Output' column for step 3 in the execution_table.

At which step does the script add the total sales line to the report?

A Step 2

B Step 3

C Step 4

D Step 5

💡 Hint

Look at the 'Action' column in the execution_table for when the sales line is appended.

If the > operator at step 3 was changed to >>, what would happen?

A The header line would be appended to existing content.

B The script would fail to write the file.

C The report file would be overwritten each time.

D The date variable would change.

💡 Hint

Refer to the key_moments explanation about > vs >> operators.

Concept Snapshot

Report generation script in bash:
- Use variables to store data (e.g., name, date)
- Use > to create/overwrite files, >> to append
- Use echo to write lines to the report
- Use $(command) to capture command output
- Display report with cat or similar
- Script runs step-by-step to build report file

Full Transcript

This bash script starts by setting a variable 'name' to hold the report title. Then it captures the current date into the 'date' variable using the date command. Next, it writes the title and date into a new file called report.txt using the > operator, which creates or overwrites the file. After that, it appends a line with total sales using >> so the existing content is kept. Finally, it displays the content of report.txt using cat. The script ends after showing the report. Variables change as the script runs: 'name' and 'date' hold strings, and the report.txt file grows from empty to containing two lines. Key points include understanding the difference between > and >> for file writing, and how command substitution $(...) captures output into variables. The visual quiz tests understanding of file content after each step and the effect of changing operators.

Practice

1. What is the main purpose of a report generation script in bash?

easy

A. To automatically collect and save information into a file

B. To compile source code into an executable

C. To delete all files in a directory

D. To open a graphical user interface

Solution

1. Step 1: Understand the script's goal

   A report generation script is designed to gather data and save it for review.

2. Step 2: Match purpose with options

   Only To automatically collect and save information into a file describes collecting and saving information automatically.

3. Final Answer:

   To automatically collect and save information into a file -> Option A

4. Quick Check:

   Report generation = collect and save info [OK]

Hint: Think: What does 'report generation' mean? Collect and save! [OK]

Common Mistakes:

• Confusing report generation with compiling code
• Thinking it deletes files
• Assuming it opens GUIs

2. Which line correctly starts a bash script for report generation?

easy

A. echo "Start script"

B. #!/bin/python

C. #!/bin/bash

D. import bash

Solution

1. Step 1: Identify the correct shebang for bash

   The first line in a bash script must be #!/bin/bash to specify the interpreter.

2. Step 2: Check other options

   Options B, C, and D are either for other languages or commands, not the script start line.

3. Final Answer:

   #!/bin/bash -> Option C

4. Quick Check:

   Shebang for bash = #!/bin/bash [OK]

Hint: Always start bash scripts with #!/bin/bash [OK]

Common Mistakes:

• Using wrong interpreter path
• Starting with commands instead of shebang
• Confusing bash with python

3. What will be the output of this script?

#!/bin/bash

filename="report.txt"
echo "Report generated on: $(date)" > $filename
echo "User count: $(who | wc -l)" >> $filename
cat $filename

medium

A. Shows an error because of wrong variable usage

B. Prints current date and number of logged-in users in report.txt

C. Prints only the date, not user count

D. Creates an empty file named report.txt

Solution

1. Step 1: Analyze echo commands and redirection

   The first echo writes the date line to report.txt (overwrite). The second echo appends user count.

2. Step 2: Understand the final cat command

   cat prints the contents of report.txt, showing both lines.

3. Final Answer:

   Prints current date and number of logged-in users in report.txt -> Option B

4. Quick Check:

   echo > overwrite, echo >> append, cat prints file [OK]

Hint: Remember > overwrites, >> appends in bash [OK]

Common Mistakes:

• Confusing > and >> operators
• Thinking variable usage is wrong
• Assuming file is empty

4. Identify the error in this report generation script snippet:

#!/bin/bash
filename=report.txt
echo "Start report" > $filename
echo "Date: $(date)" > $filename
cat $filename

medium

A. The second echo overwrites the file, losing the first line

B. The variable filename is not defined correctly

C. Missing execute permission on the script

D. The cat command is incorrect

Solution

1. Step 1: Check file redirection operators

   The first echo writes "Start report" to the file. The second echo uses > again, overwriting the file.

2. Step 2: Understand the effect on output

   Because of overwrite, the first line is lost. Only the date line remains in the file.

3. Final Answer:

   The second echo overwrites the file, losing the first line -> Option A

4. Quick Check:

   Using > twice overwrites file [OK]

Hint: Use >> to append, not > to avoid overwriting [OK]

Common Mistakes:

• Assuming > appends instead of overwriting
• Thinking variable is undefined
• Blaming cat command

5. You want to create a report script that lists all files in the current directory and their sizes, saving to files_report.txt. Which script snippet correctly does this?

hard

A. #!/bin/bash
ls -l > files_report.txt

B. #!/bin/bash
ls -l >> files_report.txt
ls -a > files_report.txt

C. #!/bin/bash
ls -lh > files_report.txt

D. #!/bin/bash
ls -lh > files_report.txt
wc -l >> files_report.txt

Solution

1. Step 1: Understand the requirements

   The report must list files with sizes and save to files_report.txt.

2. Step 2: Analyze options for correct commands and output

   #!/bin/bash ls -lh > files_report.txt wc -l >> files_report.txt uses ls -lh for human-readable sizes and writes to the file. Then it appends the line count with wc -l, adding useful info.

3. Step 3: Check other options

   #!/bin/bash ls -l > files_report.txt lacks human-readable sizes. #!/bin/bash ls -l >> files_report.txt ls -a > files_report.txt overwrites file after appending, losing data. #!/bin/bash ls -lh > files_report.txt misses line count info.

4. Final Answer:

   Option D correctly lists files with sizes and appends line count to the report -> Option D

5. Quick Check:

   ls -lh for sizes + wc -l appended = correct report [OK]

Hint: Use ls -lh for sizes and append extra info with >> [OK]

Common Mistakes:

• Overwriting file after appending
• Not using human-readable size option
• Missing extra useful info like line count