CURL vs WGET, Process Priority, nohup, /proc, AWK, GREP & SED (Beginner-Friendly Guide)

Today was packed with extremely practical Linux concepts used daily in API testing, automation, monitoring, and log analysis.
Here’s a detailed breakdown of everything I learned, explained simply with clear examples and visuals 👇

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🌐 1️⃣ CURL vs WGET— Understanding the Difference

Today I learned the real purpose of these two powerful commands:

🟦 wget

• Download files from the internet

• Simple and reliable

• Great for grabbing large binaries, tar files, etc.

🟧 curl

• Can download AND upload

• Supports POST/PUT requests

• Supports FTP/SFTP

• Highly used in API testing

🔀 Handling Redirect URLs

When using shortened links like bit.ly, they redirect to another site.

• curl:

    curl -L <url>
  

• wget:

    wget --max-redirect=10 <url>
  

📡 API Testing with cURL

curl -X POST <url>

This allows interacting with APIs directly from Linux — extremely useful for DevOps/DevSecOps pipelines.

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⚙️ 2️⃣ Process Priority, nohup & The /proc Directory

📊 Setting Process Priority

I learned how to control how much CPU a process should get:

nice -n 10 ./longjob.sh

Higher numbers = lower priority.

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🔄 nohup — Keep Processes Running Even After Logout

nohup ./script.sh &

• Makes the process immune to disconnections

• Perfect for long-running background tasks

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📁 Understanding /proc Directory

• /proc contains virtual files representing system and process information.

• Shows live data: memory, CPU usage, process status, etc.

• Great for debugging & monitoring performance.

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📝 3️⃣ Text Processing Tools — AWK, GREP & SED

These three tools are the backbone of log analysis and data filtering in Linux.

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🟡 AWK — The Text Processing Powerhouse

AWK works with columns and delimiters.
Example text:

Max Rodriguez

• Max → Column 1 ($1)

• Rodriguez → Column 2 ($2)

📌 Common AWK Commands

• print $0 → entire line

• print $1 → first word

• print $2 → second word

📐 General Format

awk 'pattern { action }' file.txt

🧪 Example

Print rows where the 4th column is greater than 5000:

awk '$4 > 5000 {print $1, $4}' 1.txt

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🔵 GREP — Searching & Filtering Text

Grep helps find specific patterns in huge logs or datasets.

🔍 Common Flags

• -i → ignore case

• -v → inverse match

• -n → show line numbers

• -c → count matches

• -E → extended regex

• -r → recursive search

• -w → exact word

📌 Useful Patterns

• ^A → lines starting with “A”

• New York$ → lines ending with “New York”

Perfect for filtering logs, API responses, and system messages.

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🔴 SED — Stream Editor for Editing Text

SED helps modify files without opening them.

📄 Common Commands

1️⃣ Suppress output

sed -n

2️⃣ Print the 3rd line

sed -n '3p' 1.txt

3️⃣ Print lines 2 to 4

sed -n '2,4p' 1.txt

4️⃣ Append after a line

sed '3a\This is a new line' 1.txt

5️⃣ Insert before a line

sed '1i\This is a new line' 1.txt

SED becomes extremely useful during automation, CI/CD scripts, and configuration changes.

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🎯 Day 5 Takeaway

Today strengthened my understanding of:
✔️ API testing using cURL
✔️ Priority management using nice
✔️ Persistent background processing with nohup
✔️ Understanding Linux internals via /proc
✔️ Text processing (AWK, GREP, SED) — crucial for handling logs and automation

Each day, the Linux foundation becomes clearer — helping me build the strong fundamentals needed for DevSecOps.

See you on Day 6! 🚀