Linux built-in commands

Main shell built-in commands

The shell has a lot of commands built into its source code. These commands are built-in, so the shell does not have to search for them on the disk and the execution speed is accelerated. Different shell built-in commands vary.

a.2.1 Bash built-in commands

.: Executes the program in the current process environment. With source.

. The File:dot command reads the command from the file and executes it.

: null operation, return exit status 0.

Alias: Displays and creates an alias for an existing command.

BG: Put your homework in the background.

Bind: Displays the current keyword's binding to the function, or binds the keyword to a readline function or macro.

Break: Jumps out of the inner loop.

Builtin [Sh-builtin [args]]: runs a built-in shell command and transmits parameters, returning exit status 0. This command is useful when a function has the same name as a built-in command.

CD [ARG]: Change directory, if no parameters, go back to the home directory, with parameters switch to the directory referred to by the parameter.

Command COMAND [ARG]: Executes the command even if there is a function with the same name. That is, skipping the function lookup.

DECLARE [VAR]: Displays all variables, or declares variables with optional attributes.

Dirs: Displays the directory of the current record (the result of the pushd).

Disown: Deletes an active job from the job table.

echo [args]: Displays args and wraps.

Enable: Enables or disables commands built into the shell.

eval [args]: reads args into the shell and executes the resulting command.

EXEC command: Run commands to replace the current shell.

Exit [n]: Exit the shell with State N.

Export [var]: Make the variable readable by the quilt shell.

FC: History of the Modify command, used to edit history commands.

FG: Put the background work in the foreground.

Getopts: Parses and Processes command-line options.

Hash: Controls the internal hash table used to speed up command lookups.

Help [command]: Displays useful information about the built-in commands. If you specify a command, the details of the command are displayed.

History: Displays a list of command histories with line numbers.

Jobs: Displays the job put in the background.

Kill [-signal Process]: sends a signal to the process specified by the PID number or job number. Enter Kill-l to view the list of signals.

Let: Used to calculate the value of an arithmetic expression and assign the result of an arithmetic operation to a variable.

Local: In the function, limit the scope of the variable to the inside of the function.

Logout: Exit login shell.

POPD: Deletes an item from the directory stack.

PUSHD: Adds an item to the directory stack.

PWD: Prints out the current working directory.

Read [VAR]: reads a row from the standard input and saves it to the variable var.

ReadOnly [var]: variable var is set to read-only and is not allowed to reset the variable.

return [n]: Exit from function, n is the exit status value assigned to the return command.

Set: Sets options and positional parameters.

Shift [n]: Shifts the positional parameter n times to the left.

Stop PID: Pauses the operation of the PID number process.

Suspend: Terminates the operation of the current shell (not valid for login shell).

Test: Check the file type and evaluate the conditional expression.

Times: Displays the cumulative user time and system time that the process started by the current shell runs.

Trap [ARG] [n]: executes ARG when the shell receives a signal n (n is 0, 1, 2, or 15).

Type [command]: Displays the types of commands, for example: PWD is a built-in command for the shell.

Typeset: With declare. Sets the variable and assigns its properties.

Ulimit: Displays or sets the maximum amount of resources available for the process.

Umask [octal number]: User files Create pattern masks for owners, genera groups, and other users.

Unalias: Cancels all command alias settings.

unset [name]: Cancels the value of the specified variable or the definition of the function.

Wait [pid#n]: Wait for the background process with PID number N to end and report its end status.

Linux built-in commands