Day-4 text processing cmnds In Linux

📄 What is Text Processing?

Text processing means working with text data to read, change, organize, or analyze it.

• It involves manipulating the actual content of text files or streams.

• You can extract parts of the text, replace words, count data, sort lines, or format output.

• It’s like editing or analyzing text to get useful information.

Example:

• Extracting usernames from a file.

• Changing all "error" words to "warning".

• Counting how many words are in a documents

Linux Text Processing Commands

• sed — Stream editor to find & replace text, filter lines

• awk — Powerful column/field extraction and processing tool

• cut — Extract specific columns or character ranges

• sort — Sort lines alphabetically or numerically

• uniq — Remove duplicate adjacent lines

• tr — Translate or delete characters (e.g., case conversion)

• wc — Count lines, words, characters

✅ 1. awk — Extract and process columns

awk is a powerful text-processing tool that works on column-based data.

Syntax:

awk '{print $1, $3}' filename

Example:
File: data.txt

Alice 24 Engineer
Bob 30 Doctor
Cara 28 Teacher

Command:

awk '{print $1, $3}' data.txt

Output:

Alice Engineer
Bob Doctor
Cara Teacher

📌 Explanation: Prints 1st and 3rd columns (Name and Job).

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✅ 2. sed — Replace or edit text

. sed — Stream editor for text substitution and filtering

sed stands for stream editor, which is used to search a word in the file and replace it with the word required to be in the output

Note: it will only modify the output, but there will be no change in the original file.

sed is a stream editor used to find and replace text or edit in-place.

Syntax:

sed 's/old/new/' filename

Example:

echo "I like cats" | sed 's/cats/dogs/'

Output:

I like dogs

📌 Explanation: Replaces the word "cats" with "dogs".

To replace in a file permanently:

sed -i 's/cats/dogs/' file.txt

Syntax:

sed 's/old/new/g' filename

Example:
File: file.txt

Hello world
Hello everyone

Command:

sed 's/Hello/Hi/g' file.txt

Output:

Hi world
Hi everyone

• 📌 Explanation:
  Replaces all occurrences of "Hello" with "Hi" in each line.

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4. cut — Extract specific columns or characters

Syntax:

cut -d'delimiter' -f field_numbers filename

Example:
File: /etc/passwd (sample line)

root:x:0:0:root:/root:/bin/bash

Command:

cut -d':' -f1 /etc/passwd

Output:

root

📌 Explanation:
Extracts and prints the first field (username) from colon-separated lines.

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5. sort — Sort lines in a file

Syntax:

sort filename

Example:
File: names.txt

Bob
Alice
Cara

Command:

sort names.txt

Output:

Alice
Bob
Cara

📌 Explanation:
Sorts lines alphabetically in ascending order.

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6. uniq — Filter duplicate adjacent lines

Syntax:

uniq filename

Example:
File: sorted.txt

Alice
Alice
Bob
Cara
Cara
Cara

Command:

uniq sorted.txt

Output:

Alice
Bob
Cara

📌 Explanation:
Removes duplicate consecutive lines (use sort first for non-adjacent duplicates).

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7. tr — Translate or delete characters

Syntax:

tr SET1 SET2

Example:

echo 'hello' | tr 'a-z' 'A-Z'

Output:

HELLO

📌 Explanation:
Converts all lowercase letters to uppercase.

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8. wc — Count lines, words, characters

Syntax:

wc -l filename

Example:
File: file.txt

Hello world
This is Linux

Command:

wc -l file.txt

Output:

2 file.txt

📌 Explanation:
Counts the number of lines in the file.

🧠 Linux Filter Commands – Quick Reference Table