cat

Concatenate files and print on the standard output.

Synopsis

cat [OPTION]... [FILE]...

Main Purpose

• Display file contents. If no file is specified, or if the file is -, read from standard input.
• Concatenate the contents of multiple files and print them to standard output.
• Display non-printing characters (control characters, newlines, tabs, etc.) in the file content.

Parameters

FILE (optional): The file(s) to be processed. One or more files can be specified.

Options

Long options are equivalent to short options.

-A, --show-all           Equivalent to the combined option "-vET".
-b, --number-nonblank    Number non-empty output lines, starting from 1, overriding the "-n" option.
-e                       Equivalent to the combined option "-vE".
-E, --show-ends          Display a '$' character at the end of each line.
-n, --number             Number all output lines, starting from 1.
-s, --squeeze-blank      Suppress repeated empty output lines.
-t                       Equivalent to the combined option "-vT".
-T, --show-tabs          Display TAB characters as "^I".
-u                       POSIX compatibility option, has no effect.
-v, --show-nonprinting   Use "^" and "M-" notation for control characters, except for LFD (line feed, '\n') and TAB.

--help                   Display help information and exit.
--version                Output version information and exit.

Return Value

Returns success unless an invalid option or parameter is provided.

Examples

# Concatenate and display multiple files
cat ./1.log ./2.log ./3.log
# Display non-printing characters, tabs, and newlines in a file
cat -A test.log
# Squeeze empty lines in a file
cat -s test.log
# Display a file and append line numbers to the beginning of all lines
cat -n test.log
# Display a file and append line numbers to the beginning of all non-empty lines
cat -b test.log
# Display standard input content together with file content
echo '######' | cat - test.log

Notes

1. This command is part of the GNU coreutils package; for related help information, please refer to man -s 1 cat or info coreutils 'cat invocation'.
2. When using the cat command to view large files, the text flashes across the screen (scrolling) so quickly that users often cannot see the content. To control the scrolling, press Ctrl+s to stop; press Ctrl+q to resume; press Ctrl+c (interrupt) to terminate the command and return to the shell prompt.
3. It is recommended to use less, more, or text editors like emacs or vi when viewing large files.

Reference Links

1. Question about LFD key