Linux cat Command

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The cat (full English: concatenate) command is used to concatenate files and print them to the standard output device. Its main purpose is to view and concatenate files.

Permissions

All users

Syntax

cat [选项] [文件]

Parameter description:

  • -n: Display line numbers, adding a line number before each line of output.
  • -b: Display line numbers, but number only non-blank lines.
  • -s: Squeeze consecutive blank lines into a single blank line.
  • -E: Display at the end of each line$the symbol.
  • -T: Display Tab characters as^I。
  • -v: Display some non-printing characters.

Usage instructions:

  • Display file content:cat filenameIt will output the content of the specified file to the terminal.

  • Concatenate files:cat file1 file2 > combined_fileYou can concatenate the contents of file1 and file2 and output the result to combined_file.

  • Create a file: you can usecatcommand to create a file, for examplecat > filename, then you can enter text and pressCtrl+Dto save and exit.

  • Display file in terminal: you can usecatwith a pipe (|) in combination to display the output of other commands, for examplels -l | catwillls -l's output throughcatprinted to the terminal.

Examples

View file content:Displays the content of the file filename.

cat filename

Create a file:Redirect standard input to the file filename, overwriting the file's content.

cat > filename

Append content to a file:Append standard input to the end of the file filename.

cat >> filename

Concatenate files:Merge the contents of file1 and file2 into file3.

cat file1 file2 > file3

Display the contents of multiple files:Display the contents of file1 and file2 at the same time.

cat file1 file2

Using pipes:Use the output of the cat command as input to another command.

cat filename | command

View the last few lines of a file:Displays the last 10 lines of the file filename.

cat filename | tail -n 10

Use the -n option to display line numbers:Displays the content of the file filename and adds a line number before each line.

cat -n filename

Use the -b option to display line numbers only for non-blank lines:

cat -b filename

Use the -s option to merge blank lines:Displays the content of the file filename and collapses consecutive blank lines.

cat -s filename

Use the -t option to display tab characters:Displays the content of the file filename, using ^I to represent tab characters.

cat -t filename

Use the -e option to display end-of-line characters:Displays the content of the file filename, using $ to represent the end of a line.

cat -e filename

Add line numbers to the contents of textfile1 and output to textfile2:

cat -n textfile1 > textfile2

Add line numbers to the contents of textfile1 and textfile2 (excluding blank lines) and then append the result to textfile3:

cat -b textfile1 textfile2 >> textfile3

Clear the contents of /etc/test.txt:

cat /dev/null > /etc/test.txt

cat can also be used to create image files. For example, to create a floppy disk image, insert the floppy disk and type:

cat /dev/fd0 > OUTFILE

Conversely, if you want to write an image file to a floppy disk, type:

cat IMG_FILE > /dev/fd0

Note：

  • 1. OUTFILE refers to the output image file name.
  • 2. IMG_FILE refers to the image file.
  • 3. When writing back from the image file to the device, the device capacity must be equivalent.
  • 4. Usually used to create boot disks.

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