xd

NAME

xd - eXtra fast Directory changer

SYNOPSIS

xd [OPTIONS] arguments

DESCRIPTION

The program xd is used to perform eXtra fast Directory changes. Usually to change a directory the user is required to enter a command like, e.g., cd /usr/local/bin, possibly using shell completion. Often this is a tedious task: shell completion shows all entries, including files, when we’re only interested in directories and the full specification of our intented directory may eventually require many keyboard actions.

Note: xd version 4.00.00 introduces several new modes of operation: see section VERSION 4.00.00 for details.

Xd was designed a long time ago (in the early 90s) to reduce the effort of changing directories. Often we’re well aware to which directory we want to change, and it’s easy to provide the initial directory characters of that directory. E.g., if the intent is to cd to /usr/local/bin, it’s easy to specify the letters ulb.

Xd capitalizes on this capability. By providing the initial directory characters of directories xd determines the expansion(s) allowing you to do fast directory changes. So, after entering the command xd ulb xd may directly perform the change-directory to /usr/local/bin.

Often, however, multiple alternatives can match the specified series of characters. E.g., when entering xd ulb xd may find several alternatives, like

1: /usr/lib/base-config
2: /usr/lib/bonobo
3: /usr/lib/bonobo-activation
4: /usr/local/bin

If these are the alternatives, then this is exactly what xd shows you. Then, by simply pressing the 4 key (no Enter key required) xd performs the required /usr/local/bin.

Xd’s behavious can be fine-tuned in various ways:

	o		by default (as specified by the configuration file, see below) xd looks for expansions starting at the user’s home directory or at the system’s root directory;
	o		initial character /: if the first character of the command is / then all expansions are performed from the system’s root directory. E.g., xd /t produces /tmp but not /home/user/tmp;
	o		initial character .: if the first character of the command is . then by default all expansions are performed from the user’s home directory. E.g., xd .t results in /home/user/tmp but not in /tmp. The home directory recognition character can be altered using the --homedir-char option, see below (section OPTIONS);
	o		initial character 0: If the first character of the command is 0, then all expansions start at the current working directory. In fact, this is a specialization of the following, more general form:
	o		initial character 1..9: If the first character of the command is a digit between 1 and 9 then all expansions start at that parent directory level of the current working directory (up to the system’s root directory). E.g., if the current working directory is /usr/share/doc then xd 2lb will offer the alternative /usr/local/bin: two steps up, then look for directories starting with l and therein directories starting with b;
	o		separators (space, and the forward slash (’/’)): sometimes it is clear that there are many alternatives and the intention is to reduce that number. By using separators subsequently nested directories must start with the characters between the separators. E.g., xd u l bi doesn’t produce the alternative /usr/lib/base-config anymore, since base-config does not start with bi. In this case only /usr/local/bin is produced. When used as initial character in a pattern the forward slash always indicates the root-directory;
	o		search patterns may contain dots (like .s). In such cases the dot represents hidden directories. However, xd usually also finds patterns containing /./, as the current directory matches the dot. Such patterns are considered spurious and are not reported.

If there’s only one solution, Xd prepares for a directory change to the solution’s directory.

If there are multiple solutions, then by default (but see also section VERSION 4.00.00) lists of at most 62 alternatives (10 for the numbers 0..9, 26 for the letters a..z and 26 for the letters A..Z) are written to the standard error stream from which the user may select an alternative by simply pressing the key associated with the selection of choice. If no selection is requested any other key may be pressed (e.g., the space bar or the Enter key). If there is no solutioon xd writes the text No Solutions to the standard error stream.

When xd is given at least one argument, all its output is sent to the standard error stream, except for the selected directory name which should become the next working directory.

If no selection is made or if the selection process is aborted a single dot is written to the standard output stream. Usually xd will be called by a shell alias, providing the cd command with xd’s output (see below at the SHELL SCRIPTS section) executing cd ’xd $*’. The default dot produced by xd prevents an unintended change of directory.

When xd is merely given an initial directory specification, like a single dot (.) or digit (a digit in the set [0..9]) then xd returns the implied path. Specifying a parent before the root-directory (E.g., entering ’xd 5’ when the current working directory is ’/tmp’) results in writing the root directory (’/’) to the standard output stream.

If xd is called without arguments its usage information is written to the standard error stream.

Xd may be further configured using options and a configuration file, discussed in the OPTIONS and CONFIGURATION FILE sections below.

VERSION 4.00.00

Starting with xd version 4.00.00 several major changes were implemented:

o

xd may insert the cd command directly into the command shell from where xd was called.

Before version 4.00.00 the selected directory was written to the standard output stream, where a a shell alias or script, passes xd’s output to the cd command (cf. section SHELL SCRIPTS). In this mode of operation xd returns a single dot if no selection is made, preventing an unintended change of directory.

This mode of operation is still xd’s default mode of operation. By specifying option --input (or by entering input in the configuration file) the additional shell alias or script is no longer necessary. In this input mode xd directly inserts the requested cd command into the shell’s input buffer. This mode has an additional feature: if a key is pressed that is not assiciated with a possible directory then the current directory is kept, and the character corresponding to the pressed key is entered into the shell’s input buffer. E.g., if xd ulb shows a list of five alternatives, but the L key is pressed then xd ends and the shell’s input buffer shows l. Merely pressing s + Enter will then show the current directory content. To merely end xd in this mode the space bar or Enter key can be pressed;

o

the option --block-size <nr> (or specifying block-size <nr> in the configuration file), the possible directories matching xd’s argument are listed in blocks of <nr> elements. The built-in minimum block size is 5. If there are fewer alternatives then this built-in minimum then the actually available alternatives are displayed;

When alternatives are split up in blocks, a + is displayed after listing the first block, a - is displayed after listing the last block, and -+ is displayed after listing the intermediate blocks. In these cases, pressing - redisplays the previous block, pressing + displays the next block;

Although these block-end prompts only show - and +, the characters , and < (usually combined in one key) can be used instead of -, while . and > (also usually combined in one key) can be used instead of +.

GENERALIZED DIRECTORY SEARCH

Xd also supports generalized directory search commands (GDS). When GDS is requested separators are no longer required, and xd finds all possible alternatives resulting from all possible sequential combinations of the initial search command. GDS is activated either by specifying the -g option or by entering generalized-search in xd’s configuration file. Alternatively, when the latter is specified then the --traditional command line option suppresses GDS.

When using GDS each initial substring of the command to xd is considered as the initial characters of a directory. E.g., if the command xd tmps is entered using GDS then directories matching the following search patterns will be found;

	o		/t*/m*/p*/s*/
	o		/t*/m*/ps*/
	o		/t*/mp*/s*/
	o		/t*/mps*/
	o		/tm*/p*/s*/
	o		/tm*/ps*/
	o		/tmp*/s*/
	o		/tmps*/ With the traditional processing mode only the first one of these alternative patterns is considered.

Multiple command line arguments, the slash, and the underscore can still be used with GDS. In this case they force a directory change using the considered patterns. E.g., with the command xd tm/ps the following patterns will be considered:

	o		/t*/m*/p*/s*/
	o		/t*/m*/ps*/
	o		/tm*/p*/s*/
	o		/tm*/ps*/ In this set all of the previous patterns showing the ...mp... combination were dropped, as a directory change is forced between the m and p characters.

RETURN VALUES

Xd may return the following values to its caller, allowing scripts calling xd to make decisions that depend on the actually performed action by xd:

	o		0 is returned if xd issued a cd command;
	o		1 is returned if xd received a non-space character, not selecting a directory to change to. When the input option has been specified this character is inserted into the command shell’s input buffer;
	o		2 is returned if xd received a space (or Enter) character, indicating that xd should perform no further action;
	o		3 is returned if no directory was found matching the argument passed to xd;
	o		4 is returned if the --help or --version option was specified (see their descriptions in the OPTIONS section);
	o		5 is returned if an error was encountered (e.g., when a non-existing configuration file is specified).

OPTIONS

If available, single letter options are listed between parentheses following their associated long-option variants. Single letter options require arguments if their associated long options require arguments as well.

Most options can also be specified in xd’s configuration file, in which case the long option variants must be used, omitting the initial two dashes (see the section CONFIGURATION FILE below for specific details about the configuration file.

By default the options can also be specified in the configuration file. If an option cannot be specifiied in the configuration file it is explicitly stated at its description.

Options that are specified as command-line options take priority over options specified in the configuration file.

o

--add-root condition

If the search starts at the user’s home directory an additional search starting at the system’s root directory may be performed as well, depending on the value specified for the add-root option. Conditions are

	o		never (no additional search is performed),
	o		if-empty (an additional search is performed if the initial search did not yield any directory),
	o		always (an additional search is always performed);
	o

--all -a
If the configuration file (see below) contains ignore directives then those directives are ignored when computing the alternatives from which the user may select a directory to change to;

o

--block-size=nr (-b)

The possible directories matching xd’s argument are listed in blocks of <nr> elements. See also the previous section VERSION 4.00.00,

o

--config-file=filename (-c)

The name of an xd configuration file. By default xd looks for the file .xdrc in the user’s home directory. The existence of the default file is optional.

This option cannot be specified in the configuration file;

o

--directories inclusion

Directories may be also be reached via symbolic links. The (default) inclusion type all adds these symbolic links to the list of alternatives. The inclusion type unique prevents symbolic links from being added to the list of alternatives;

o

--generalized-search -g

When specified xd uses GDS unless the directive traditional is specified in the configuration file;

o

--help (-h)

Basic usage information is written to the standard error stream, whereafter xd terminates.

This option cannot be specified in the configuration file;

o

--homedir-char ch

By default an initial dot character (’.’) initiates a search from the user’s home directory. There is a slight disadvantage to using the dot, as it is also be the initial character of ’hidden’ directories. Assuming that you have a directory ~/.ssh then the command to xd to that directory would be xd ..s, the first dot being the home directory indicator, after which .s is used to find .ssh. The option --homedir-char can be used to specify another character. Homedir characters cannot be digits or a slash (’/’) as these are used to specify, respectively, parent directories and the computer’s root directory. Characters like ’’, @ % ^’’ or maybe ’H’ (assuming that it doesn’t interfere with an existing directory beginning with H) could be used as homedir-characters, other than the default dot character.

Caveat: command shells by default interpret characters like ’’~ $ ’ " ’ < > |’’ etc., which therefore should probably not be specified as home directory specifiers;

o

--history [filename]

A history of previously made choices is kept in the file filename. If --history is specified, but the filename is left empty the history file $HOME/.xd.his is used. This file should only be modified by xd itself. If you can’t resist editing it then use the following example showing the format of the lines in the history file.

1292596154 1 /home/frank/svn/xd/

The first field is the time (in seconds since the epoch) the entry was written, the second field is the number of times the entry has been selected and the third field is the associated path.

The following history-... options are only interpreted if the history option is also specified.

o

--history-lifetime spec

The lifetime of the entries in the history file. The specification consists of a number followed by D, W, M or Y, representing, resp. days, weeks, months, or years. A month is considered a period of 30 days, a year a period of 365 days. If the specification is omitted a lifetime of 1M (one month) is used. Entries older than history-lifetime are disregarded as history-items and are removed from the history file;

o

--history-maxsize nr

The maximum number of entries the history file may contain. By default there is no limit. When history-maxsize is specified and more than the maximum number of history items are found in the history file then the nr most popular choices are kept. Usually the cut-off point will be somewhere within a popularity category. In that case the most recently selected alternatives within that category are kept;

o

--history-position [top|bottom]

Previously found alternatives are displayed either at the top of the list or at the bottom of the list. If this option is omitted then the elements in the history are intermixed with new alternatives. The next option history-separate is only used when this option is also specified. By merely specifying history-position the history items are shown at the top of the list;

o

--history-separate

When specified a blank line is written between the items in the history and new alternatives (not previously selected). This option is only interpreted when the previous option is also specified;

o

--icase -i

Specify this option to use case-insensitive pattern matching. E.g., specifying xd /ub returns the directory /usr/bin, but not a directory like /UnSpecified/Books, which is returned by xd /UB. However, xd -i /ub (using any letter casing for the specification) returns both directories. The option icase could of course be specified in the configuration file, which which case case-insensitive matching is used by default. In the latter case specifying -i as a command line option reverts the matching procedure to case-sensitive directory matching. In general, when an even number of icase specifications is provided xd uses case-sensitive directory matching, while an odd number of icase specifications results in case-insensitive directory matching;

o

ignore path

This option cannot be specified as command-line option. Instead, the configuration file may contain multiple ignore directives which are (different from the way other directives are handled) all interpreted. Each ignore directive is followed by a path specification as shown in a list of alternatives produced by xd or an initial substring of such a path terminating in a * character. When xd encounters a path matching any of the ignore directives (interpreting the final * as ’any further directory name’ specification) it will not display that path in its list of alternatives.

This directive is overruled by the ---all command line option;

o

--input

Xd itself issues the cd command for the selected directory to the shell, and enters other (non alternative-selecting characters) into the shell’s input. See also the previous section VERSION 4.00.00. See also option no-input.

To merely end xd press the Enter key or space-bar;

o

--no-input

The no-input option can only be specified as a command-line option and suppresses the input option. The no-input option has no effect if the input option is not specified.

By suppressing the input mode xd writes the name of the directory to change to to its standard output stream. This allows shell functions to process the directory returned by xd. An example of its use is the function pxd (pushd using xd) shown in section SHELL SCRIPTS;

o

--start-at origin

Defines the default start location of directory searches. Origin home (the default) results in all default searches to start at the user’s home directory. Origin root results in searches to begin at the disk’s root (/) directory;

o

--traditional

Xd does not use GDS but uses its traditional mode. It overrules a generalized-search directive specified in the configuration file as well as the -g option;

o

--verbose (-V)

More extensive information about the actions taken by the xd program is written to the standard error stream.

This option cannot be specified in the configuration file;

o

--version (-v)

Xd’s version number is written to the standard error stream whereafter xd terminates.

This option cannot be specified in the configuration file.

CONFGURATION FILE

The default configuration file is .xdrc in the user’s home directory. It may be overruled by the program’s --config-file command-line option.

Empty lines are ignored. Information at and beyond #-characters is interpreted as comment and is also ignored.

Directives in xd configuration files follow the pattern

directive value

(for some directives there is no value term).

A line may at most contain one directive, but white space (including comment at the end of the line) is OK. The same directive may be specified multiple times, in which case the last directive will be used (except for the ignore directive, which are all interpreted). All directives are interpreted case sensitively unless option icase is specified. Non-empty lines not beginning with a recognized directive are silently ignored.

SHELL SCRIPTS

Assuming xd is installed in /usr/bin scripts can be defined around xd for various shell programs. This allows the shell to change directories under control of xd.

o

Example 1.

To use xd in combination with the pushd shell command xd itself should not perform directory changes. In such cases the no-input option should be specified in the shell function combining pushd and xd.

To use xd with the bash(1)-shell, the following function can be used (which could be added to, e.g., .bash_login):

pxd() # function to do ’pushd’ using ’xd’
{
pushd "’/usr/bin/xd --no-input $*’"
}

To use xd with the tcsh(1)-shell, the following alias can be defined in, e.g., the ~/.alias file:

alias pxd ’pushd ’\xd --no-input \!*’’

o

Example 2.

If the input option is specified (as command-line or configuration file option) then this example can be ignored.

To use xd with the bash(1)-shell, the following function can be used (which could be added to, e.g., .bash_login):

xd() # function to do ’cd’ using ’xd’
{
cd "’/usr/bin/xd $*’"
}

To use xd with the tcsh(1)-shell, the following alias can be defined in, e.g., the ~/.alias file:

alias xd ’cd ’\xd \!*’’

Having defined the xd alias or script xd ... commands results in the automatic (or optional) change of the current working directory

If your system uses blanks in directory names, the above tcsh-alias cannot be used as the blanks are interpreted as argument-separaters. In that case the following alias can be defined as the xd alias:

alias xd ’setenv XD "’\xd \!*’";cd "$XD"’

EXAMPLES

xd ulb - all directories starting subsequently,
with u, l and b origin is default, or
specified in .xdrc as home or root

xd 0t - all directories starting with t below the cwd

xd 2t - all directories starting at the ’grandparent’
(2 steps up) of the cwd

xd --start-at root t
- all directories at the root starting with t

xd .. - all directories starting with a dot in the cwd

xd . - the user’s home directory

xd 0 - the current working directory

xd 1 - the current directory’s parent directory

Assuming the following directories exist:

/usr/lib/bonobo
/usr/lib/bonobo-activation
/usr/local/bin

then the following two ignore specifications in xd’s configuration file will result in ignoring the bonobo directory alternatives:

First specification:

ignore /usr/lib/bonobo
ignore /usr/lib/bonobo-activation

Second specification:

ignore /usr/lib/bonobo*

FILES

	o		$HOME/.xdrc: Default location of the configuration file
	o		https://fbb-git.gitlab.io/xd/: Home directory

BUGS

None reported

ABOUT xd

The program xd was initially (before 1994) written for the MS-DOS platform. In 1994 it was redesigned to work under Unix (Linux, AIX) and it was converted to C++. The original C++ code is still available from tag start (https://gitlab.com/fbb-git/xd/tags, find the start tag and download) and is funny to look at as it is a remarkable illustration of C++ code written by C programmers who had just learned about C++. Versions 2.x were used until 2008, and in late August 2008 I rewrote xd completely, reflecting my then views about C++, eventually resulting in versions 3.x.y and beyond. The 3.x.y and later versions extensively use the facilities offered by the bobcat(7) library.

ACKNOWLEDGEMENTS

GDS was added to xd following a suggestion by Bram Neijt (bram at neijt dot nl).

AUTHOR

Frank B. Brokken (f.b.brokken@rug.nl).