cat

🐱 cat, tac, and Piping Commands in Linux

📋 Command & Option Table

Command / Option	Description
cat file.txt	View contents of a file
cat file1 file2	Concatenate multiple files
cat > file.txt	Create a file from input (overwrites if exists)
cat >> file.txt	Append input to an existing file
cat -n file.txt	Number all lines
cat -b file.txt	Number non-empty lines only
cat -s file.txt	Squeeze multiple blank lines
cat -E file.txt	Show $ at end of each line
tac file.txt	Output file with lines in reverse order
cat file.txt | grep "term"	Pipe output to grep for searching
cat file.txt | sort	Pipe output to sort to order lines
cat file.txt | less	Pipe output to less for scrollable view

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📄 Basic Usage

View File Content

cat file.txt

View Multiple Files

cat file1.txt file2.txt

Create a File (from Input)

cat > newfile.txt

Type your content, then press Ctrl+D to save.

Append to an Existing File

cat >> existingfile.txt

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🔢 Numbering Lines

Number All Lines

cat -n file.txt

Number Non-Empty Lines Only

cat -b file.txt

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🧹 Clean Output

Squeeze Blank Lines

cat -s file.txt

Show End of Line Characters

cat -E file.txt

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🔁 Reverse Output

Use tac to Reverse Lines

tac file.txt

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📤 Piping with cat

Filter with grep

cat file.txt | grep "error"

Sort Lines

cat file.txt | sort

Scroll with less

cat file.txt | less

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📎 Merge Files into One

Save Merged Output to a New File

cat file1.txt file2.txt > merged.txt

Append More Content to Merged File

cat file3.txt >> merged.txt

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