How to Print or View Contents of File in Linux

The cat command in Linux (short for “concatenate”) is used to read, combine, and write file contents. It is one of the most versatile commands for viewing file content directly in the terminal, merging multiple files into one, creating new files, or redirecting output. While simple, it’s essential for tasks like debugging, scripting, and quick file operations.

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Display a File’s Content

cat file.txt

Prints the entire content of file.txt to the terminal.

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View Multiple Files

cat file1.txt file2.txt

Displays the contents of file1.txt and file2.txt sequentially.

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Create a New File

cat > newfile.txt

Creates newfile.txt. Type input, then press Ctrl + D to save and exit.

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Append to a File

cat >> existing_file.txt

Adds text to the end of existing_file.txt (press Ctrl + D to finish).

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Combine Files into One

cat file1.txt file2.txt > mergedfile.txt

Merges file1.txt and file2.txt into mergedfile.txt.

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Display Line Numbers

cat -n file.txt

Shows line numbers for all lines in file.txt.

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Show Non-Printable Characters

cat -v file.txt

Reveals non-printing characters (e.g., tabs as ^I).

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Concatenate with Pipes

cat file.txt | grep "keyword"

Searches for keyword in file.txt using grep.

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Reverse Output Order

tac file.txt

Prints lines in reverse order (uses tac, the reverse of cat).

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Read Input Until a Delimiter

cat << EOF > output.txt
This is line 1.
This is line 2.
EOF

Creates output.txt with lines typed between << EOF and EOF.

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Display File with Pagination

cat longfile.txt | more

Shows longfile.txt one screen at a time (use more or less).

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Create a Backup of a File

cat original.txt > backup.txt

Copies the content of original.txt to backup.txt.

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Append Multiple Files

cat file1.txt file2.txt >> combined.txt

Adds the content of file1.txt and file2.txt to combined.txt.

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View Files with Wildcards

cat *.log

Displays all .log files in the current directory.

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Remove Blank Lines

cat -s file.txt

Squeezes consecutive blank lines into a single blank line.

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Highlight Line Endings

cat -E file.txt

Displays $ at the end of each line (helps to spot trailing spaces).

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Create a Multi-Line File Quickly

cat > list.txt << EOF
Apple
Banana
Cherry
EOF

Creates list.txt with three lines of fruit names.

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Combine Binary Files

cat part1.bin part2.bin > full.bin

Merges binary files (e.g., split archives).

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Key Notes:

• Large Files: Avoid cat for huge files—use less or tail instead.
• Modifications: cat doesn’t edit files—it only reads or combines them.
• Overwriting: Use > carefully, as it overwrites existing files. Use >> to append.