chat

No standard "chat" command exists in Linux

TLDR

Execute a chat script directly from the command line

$ chat '[expect_send_pairs]'

Execute a chat script from a file

$ chat -f '[path/to/chat_script]'

Set a custom timeout (in seconds) for expecting a response

$ chat -t [timeout_in_seconds] '[expect_send_pairs]'

Enable verbose output to log the conversation to syslog

$ chat -v '[expect_send_pairs]'

Use a report file to log specific strings received during the conversation

$ chat -r [path/to/report_file] '[expect_send_pairs]'

Dial a phone number using a variable, substituting \T in the script

$ chat -T '[phone_number]' '["ATDT\\T CONNECT"]'

Include an abort condition if a specific string is received

$ chat 'ABORT "[error_string]" [expect_send_pairs]'

-A, --show-all
    Equivalent to -vET, shows non-printing characters, tabs, and line endings.

-b, --number-nonblank
    Number non-blank output lines, starting at 1. Overrides -n.

-E, --show-ends
    Display $ at the end of each line to indicate line breaks.

-n, --number
    Number all output lines, starting at 1.

-s, --squeeze-blank
    Squeeze multiple adjacent blank lines into a single blank line.

-T, --show-tabs
    Display TAB characters as ^I.

-u
    (Ignored) This option is a POSIX standard for compatibility but has no effect on modern cat implementations as output is unbuffered by default.

-v, --show-nonprinting
    Use ^ and M- notation, except for line feed (LF) and tab (TAB), to show non-printing characters.

--help
    Display a help message and exit.

--version
    Output version information and exit.

DESCRIPTION

The cat (short for "concatenate") command is a fundamental Unix and Linux utility. Its primary function is to read file content sequentially and write it to standard output. While its name implies concatenation, its most common modern usage is simply to display the content of one or more files directly to the terminal. Beyond mere viewing, cat is also widely used for combining multiple files into a single output stream or file, and for creating new files from standard input. It is an indispensable tool often employed in shell scripts and command pipelines, typically in conjunction with input/output redirection operators (like > for overwriting, >> for appending) or pipes (|) to feed file content to other commands for further processing.

CAVEATS

When dealing with very large files, cat loads the entire content into memory (or buffers it to standard output), which can be inefficient and consume significant resources. For interactive viewing of large files, commands like less or more are generally preferred as they allow scrolling and do not load the entire file at once.

Be cautious when redirecting output using the > operator (e.g., cat file1 > file2), as it will overwrite the destination file (file2 in this example) without warning if it already exists. Use >> to append instead (e.g., cat file1 >> file2).

STANDARD INPUT/OUTPUT

When no FILE is specified, or when FILE is given as a single hyphen (-), cat reads from its standard input until an end-of-file (EOF) signal is received (typically by pressing Ctrl+D). This makes it incredibly versatile for use in pipelines, where it can process output from other commands. For example, command | cat - file2 > combined_file allows you to concatenate the output of 'command' with 'file2' into 'combined_file'.

HISTORY

The cat command is one of the earliest Unix commands, predating the C programming language itself. It was originally implemented in assembly language for the PDP-7. Its name is derived from "concatenate," reflecting its initial primary purpose of joining files. While still capable of concatenation, its most prevalent modern use, displaying file contents on the standard output, was somewhat an unintended consequence of its design, often humorously referred to as an "abuse" by its original developers.