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PROLOG
This manual page is part of the POSIX Programmer's Manual. The Linux implementation of
this interface may differ (consult the corresponding Linux manual page for details of
Linux behavior), or the interface may not be implemented on Linux.
NAME
alias — define or display aliases
SYNOPSIS
alias [alias-name[=string]...]
DESCRIPTION
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 Section 2.3.1, 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 Section 2.12, Shell Execution
Environment.
OPTIONS
None.
OPERANDS
The following operands shall be supported:
alias-name
Write the alias definition to standard output.
alias-name=string
Assign the value of string to the alias alias-name.
If no operands are given, all alias definitions shall be written to standard output.
STDIN
Not used.
INPUT FILES
None.
ENVIRONMENT VARIABLES
The following environment variables shall affect the execution of alias:
LANG Provide a default value for the internationalization variables that are unset or
null. (See the Base Definitions volume of POSIX.1‐2017, Section 8.2,
Internationalization Variables for the precedence of internationalization
variables used to determine the values of locale categories.)
LC_ALL If set to a non-empty string value, override the values of all the other
internationalization variables.
LC_CTYPE 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).
LC_MESSAGES
Determine the locale that should be used to affect the format and contents of
diagnostic messages written to standard error.
NLSPATH Determine the location of message catalogs for the processing of LC_MESSAGES.
ASYNCHRONOUS EVENTS
Default.
STDOUT
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 Section 2.2, Quoting.
STDERR
The standard error shall be used only for diagnostic messages.
OUTPUT FILES
None.
EXTENDED DESCRIPTION
None.
EXIT STATUS
The following exit values shall be returned:
0 Successful completion.
>0 One of the name operands specified did not have an alias definition, or an error
occurred.
CONSEQUENCES OF ERRORS
Default.
The following sections are informative.
APPLICATION USAGE
None.
EXAMPLES
1. Create a short alias for a commonly used ls command:
alias lf="ls -CF"
2. Create a simple ``redo'' command to repeat previous entries in the command history
file:
alias r='fc -s'
3. Use 1K units for du:
alias du=du\ -k
4. Set up nohup so that it can deal with an argument that is itself an alias name:
alias nohup="nohup "
RATIONALE
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.
FUTURE DIRECTIONS
None.
SEE ALSO
Section 2.9.5, Function Definition Command
The Base Definitions volume of POSIX.1‐2017, Chapter 8, Environment Variables
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form from IEEE Std
1003.1-2017, Standard for Information Technology -- Portable Operating System Interface
(POSIX), The Open Group Base Specifications Issue 7, 2018 Edition, Copyright (C) 2018 by
the Institute of Electrical and Electronics Engineers, Inc and The Open Group. In the
event of any discrepancy between this version and the original IEEE and The Open Group
Standard, the original IEEE and The Open Group Standard is the referee document. The
original Standard can be obtained online at http://www.opengroup.org/unix/online.html .
Any typographical or formatting errors that appear in this page are most likely to have
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such errors, see https://www.kernel.org/doc/man-pages/reporting_bugs.html .