File: em-alias.el.html

Command aliases greatly simplify the definition of new commands.

They exist as an alternative to alias functions, which are otherwise quite superior, being more flexible and natural to the Emacs Lisp environment (if somewhat trickier to define; [Alias functions]).

;_* Creating aliases

The user interface is simple: type 'alias' followed by the command name followed by the definition. Argument references are made using '$1', '$2', etc., or '$*'. For example:

  alias ll 'ls -l $*'

This will cause the command 'll NEWS' to be replaced by 'ls -l NEWS'. This is then passed back to the command parser for reparsing.{Only the command text specified in the alias definition will be reparsed. Argument references (such as '$*') are handled using variable values, which means that the expansion will not be reparsed, but used directly.}

To delete an alias, specify its name without a definition:

  alias ll

Aliases are written to disk immediately after being defined or deleted. The filename in which they are kept is defined by the variable eshell-aliases-file.

The format of this file is quite basic. It specifies the alias definitions in almost exactly the same way that the user entered them, minus any argument quoting (since interpolation is not done when the file is read). Hence, it is possible to add new aliases to the alias file directly, using a text editor rather than the alias command. Or, this method can be used for editing aliases that have already defined.

Here is an example of a few different aliases, and they would appear in the aliases file:

  alias clean rm -fr **/.#*~
  alias commit cvs commit -m changes $*
  alias ll ls -l $*
  alias info (info)
  alias reindex glimpseindex -o ~/Mail
  alias compact for i in ~/Mail/**/*~*.bz2(Lk+50) { bzip2 -9v $i }

;_* Auto-correction of bad commands

When a user enters the same unknown command many times during a session, it is likely that they are experiencing a spelling difficulty associated with a certain command. To combat this, Eshell will offer to automatically define an alias for that misspelled command, once a given tolerance threshold has been reached.

Whenever the same bad command name is encountered eshell-bad-command-tolerance times, the user will be prompted in the minibuffer to provide an alias name. An alias definition will then be created which will result in an equal call to the correct name. In this way, Eshell gradually learns about the commands that the user mistypes frequently, and will automatically correct them!

Note that a '$*' is automatically appended at the end of the alias definition, so that entering it is unnecessary when specifying the corrected command name.

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