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2025-01-26 Update From: SLTechnology News&Howtos shulou NAV: SLTechnology News&Howtos > Servers >
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This article mainly shows you "what are the internal commands of Shell programming bash in Linux", the content is simple and clear, and I hope it can help you solve your doubts. Let me lead you to study and learn what are the internal commands of Shell programming bash in Linux.
The bash command interpreter suite contains some internal commands. Internal commands are not visible in the directory list, and they are provided by Shell itself. Common internal commands are: echo, eval, exec, export, readonly, read, shift, wait and dot (.).
1.echo
Command format: echo arg
Function: the string specified by arg is displayed on the screen.
2.eval
Command format: eval args
Function: when the Shell program executes the eval statement, Shell reads in the parameter args, combines them into a new command, and then executes.
3.exec
Command format: exec command parameter
Function: when Shell executes the exec statement, it does not create a new child process, but instead executes the specified command. When the specified command is executed, the process (that is, the original Shell) is terminated, so the following statements of exec in the Shell program will no longer be executed.
4.export
Command format: export variable name or: export variable name = variable value
Function: Shell can use export to bring its variables down into the child Shell, thus allowing the child process to inherit the environment variables in the parent process. But the child Shell cannot use export to bring its variables up into the parent Shell.
Note: export statements without any variable names will display all current export variables.
5.readonly
Command format: readonly variable name
Function: identifies a user-defined Shell variable as immutable. The readonly command with no arguments displays all read-only Shell variables.
6.read
Command format: read variable name table
Function: read a line from a standard input device, decompose it into several words, and assign values to variables defined within the Shell program.
7.shift statement
Function: the shift statement renames all positional variables in the following way, that is, $2 becomes $1 and 3 becomes $2. Each time the shift statement is used in the program, all the position parameters are moved one position to the left in turn, and the position parameter $# minus 1 until it is reduced to 0.
8.wait
Function: make Shell wait for the end of all child processes started in the background. The return value of wait is always true.
9.exit
Function: exit the Shell program. After exit, you can optionally specify a digit as the return state.
10. "(dot)
Command format:. Shell program file name
Function: make Shell read into the specified Shell program file and execute all the statements in the file in turn.
These are all the contents of the article "what are the internal commands for Shell programming bash in Linux?" Thank you for reading! I believe we all have a certain understanding, hope to share the content to help you, if you want to learn more knowledge, welcome to follow the industry information channel!
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