alias

Linux alias(1POSIX) command is used to define or display aliases. The alias utility shall create or redefine alias definitions or write the values of existing alias definitions to standard output.

DEFINITION
alias — define or display aliases
USAGE
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; 
An  alias  definition  shall affect the current shell execution environment and the execution environments of the subshells of the current shell,
the  alias definition shall not affect the parent process of the current shell nor any utility environment invoked by the shell;
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.1‐2008, Section 8.2, International‐
                 ization  Variables for the precedence of internationalization variables used to de‐
                 termine the values of locale categories.)

       LC_ALL    If set to a non-empty string value, override the values of all the  other  interna‐
                 tionalization 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  argu‐
                 ments).

       LC_MESSAGES
                 Determine the locale that should be used to affect the format and contents of diag‐
                 nostic 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  oc‐
             curred.

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 "

 

/* alias command will list all aliases */
root@letusstudy:~# alias
alias egrep='egrep --color=auto'
alias fgrep='fgrep --color=auto'
alias grep='grep --color=auto'
alias l='ls -CF'
alias la='ls -A'
alias listfiles='ls -ef'
alias ll='ls -alF'
alias ls='ls --color=auto'

/* ll is set as alias for command ls -alF */
root@letusstudy:~# ll
total 56
drwx------  8 root root  4096 Nov  7 12:17 ./
drwxr-xr-x 20 root root  4096 Nov  5 21:27 ../
-rw-r--r--  1 root root  3130 Nov  7 12:17 .bashrc
drwx------  6 root root  4096 Nov  6 08:48 .cache/
drwxr-xr-x  2 root root  4096 Nov  5 23:27 .composer/
drwx------  6 root root  4096 Nov  6 08:40 .config/
drwx------  3 root root  4096 Nov  6 08:39 .dbus/
-rw-r--r--  1 root root     0 Nov  7 12:16 files.txt
drwxr-xr-x  3 root root  4096 Nov  5 23:29 .local/
-rw-r--r--  1 root root     0 Nov  7 12:16 manpages.txt
-rw-------  1 root root   211 Nov  5 23:25 .mysql_history
-rw-r--r--  1 root root   161 Dec  5  2019 .profile
-rw-r--r--  1 root root     0 Nov  7 12:16 retry.pdf
drwxr-xr-x  2 root root  4096 Nov  5 23:44 .vim/
-rw-------  1 root root 12146 Nov  7 12:17 .viminfo
-rw-r--r--  1 root root     0 Nov  7 12:16 welcome.txt

/* You will see the same output for ls -alf without using alias name ll*/
root@letusstudy:~# ls -alF
total 56
drwx------  8 root root  4096 Nov  7 12:17 ./
drwxr-xr-x 20 root root  4096 Nov  5 21:27 ../
-rw-r--r--  1 root root  3130 Nov  7 12:17 .bashrc
drwx------  6 root root  4096 Nov  6 08:48 .cache/
drwxr-xr-x  2 root root  4096 Nov  5 23:27 .composer/
drwx------  6 root root  4096 Nov  6 08:40 .config/
drwx------  3 root root  4096 Nov  6 08:39 .dbus/
-rw-r--r--  1 root root     0 Nov  7 12:16 files.txt
drwxr-xr-x  3 root root  4096 Nov  5 23:29 .local/
-rw-r--r--  1 root root     0 Nov  7 12:16 manpages.txt
-rw-------  1 root root   211 Nov  5 23:25 .mysql_history
-rw-r--r--  1 root root   161 Dec  5  2019 .profile
-rw-r--r--  1 root root     0 Nov  7 12:16 retry.pdf
drwxr-xr-x  2 root root  4096 Nov  5 23:44 .vim/
-rw-------  1 root root 12146 Nov  7 12:17 .viminfo
-rw-r--r--  1 root root     0 Nov  7 12:16 welcome.txt
root@letusstudy:~# 

The alias description is based on historical KornShell implementations. Known differences ex‐ ist 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.1‐2008, 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 vol‐ ume of POSIX.1‐2008 only when an explicit extension such as −x is used. The standard develop‐ ers 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.1‐2008 has made this a requirement for all similar output. Therefore, consistency was chosen over this detail of historical practice.

FUTURE DIRECTIONS
None.

Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 7, Copyright (C) 2013 by the Institute of Electrical and Electronics Engineers, Inc and The Open Group. (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) 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 Stan‐ dard is the referee document. The original Standard can be obtained online at http://www.unix.org/online.html . Any typographical or formatting errors that appear in this page are most likely to have been introduced during the conversion of the source files to man page format. To report such er‐ rors, see https://www.kernel.org/doc/man-pages/reporting_bugs.html .

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