alias - define or display aliases
The alias utility shall create or redefine alias definitions or write the values of existing alias definitions to standard output. An alias definition provides a string value that shall replace a command name when it is encountered; see Alias Substitution.
An alias definition shall affect the current shell execution environment and the execution environments of the subshells of the current shell. When used as specified by this volume of POSIX.1-2017, the alias definition shall not affect the parent process of the current shell nor any utility environment invoked by the shell; see Shell Execution Environment.
The following operands shall be supported:
- Write the alias definition to standard output.
- Assign the value of string to the alias alias-name.
If no operands are given, all alias definitions shall be written to standard output.
The following environment variables shall affect the execution of alias:
- Provide a default value for the internationalization variables that are unset or null. (See XBD Internationalization Variables for the precedence of internationalization variables used to determine the values of locale categories.)
- If set to a non-empty string value, override the values of all the other internationalization variables.
- Determine the locale for the interpretation of sequences of bytes of text data as characters (for example, single-byte as opposed to multi-byte characters in arguments).
- Determine the locale that should be used to affect the format and contents of diagnostic messages written to standard error.
- [XSI] Determine the location of message catalogs for the processing of LC_MESSAGES.
The format for displaying aliases (when no operands or only name operands are specified) shall be:"%s=%s\n", name, value
The value string shall be written with appropriate quoting so that it is suitable for reinput to the shell. See the description of shell quoting in Quoting.
The standard error shall be used only for diagnostic messages.
The following exit values shall be returned:
- Successful completion.
- One of the name operands specified did not have an alias definition, or an error occurred.
Create a short alias for a commonly used ls command:alias lf="ls -CF"
Create a simple "redo" command to repeat previous entries in the command history file:alias r='fc -s'
Use 1K units for du:alias du=du\ -k
Set up nohup so that it can deal with an argument that is itself an alias name:alias nohup="nohup "
The alias description is based on historical KornShell implementations. Known differences exist between that and the C shell. The KornShell version was adopted to be consistent with all the other KornShell features in this volume of POSIX.1-2017, such as command line editing.
Since alias affects the current shell execution environment, it is generally provided as a shell regular built-in.
Historical versions of the KornShell have allowed aliases to be exported to scripts that are invoked by the same shell. This is triggered by the alias -x flag; it is allowed by this volume of POSIX.1-2017 only when an explicit extension such as -x is used. The standard developers considered that aliases were of use primarily to interactive users and that they should normally not affect shell scripts called by those users; functions are available to such scripts.
Historical versions of the KornShell had not written aliases in a quoted manner suitable for reentry to the shell, but this volume of POSIX.1-2017 has made this a requirement for all similar output. Therefore, consistency was chosen over this detail of historical practice.
Function Definition Command
XBD Environment Variables
First released in Issue 4.
This utility is marked as part of the User Portability Utilities option.
The APPLICATION USAGE section is added.
The alias utility is moved from the User Portability Utilities option to the Base. User Portability Utilities is now an option for interactive utilities.
SD5-XCU-ERN-97 is applied, updating the SYNOPSIS.
The first example is changed to remove the creation of an alias for a standard utility that alters its behavior to be non-conforming.
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