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Alter your bash (or zsh) environment as you cd

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README.md

smartcd - make your shell come alive

WHAT IS SMARTCD?

smartcd is a library for bash and zsh which brings transformative power to your fingertips.

The basic premise is that as you move around your computer using the shell, actions can be automatically taken to provide you with the environment you really want, not the one you're accustomed to putting up with.

Have you ever...

  • Created a file for a project to alter your environment by setting variables or creating aliases so that things work correctly, one which you need to remember to load by hand

  • Struggled to set up your shell's configuation to support conflicting needs for different uses

  • Wished that your prompt could be made to say something or be a different color when you are in a sensitive directory

  • Wanted a daemon process to run automatically when you go to work on a project, and shut down when you finish

  • Wanted to automatically update your project from source control when you enter

  • Needed to attach to a particular screen(1) session when working in a particular directory

These are just a few examples of problems people are solving with smartcd.

OK, HOW DO I USE IT?

It's stupid easy. If you have already downloaded the archive or checked out the source, you can:

make install
source ~/.smartcd/lib/core/smartcd
smartcd config

However, if you would rather skip all that and simply have it install itself, try this:

curl -L http://smartcd.org/install | bash

Either method will prompt you to configure a small number of settings, and then help you set up your shell to load it on login.

Once it is installed, you're ready to go. All actions are available through the smartcd command.

Usage: smartcd ( edit | show | filename | helper | template | setup | config ) [args]

If you run smartcd edit enter, it will launch your editor to allow you to begin creating a script for the current directory which will run when you enter. Its counterpart, smartcd edit leave, will create a script that runs when you cd away from the current directory.

An auxiliary library is provided with smartcd called varstash. This provides you with a powerful mechanism which saves the definitions of variables, aliases, and shell functions to allow you to change or unset them temporarily. Once you are finished, it will allow you to (or automatically) restore their prior values.

For example,

autostash PATH=/path/to/my/project/bin:$PATH
autostash alias restart="apachectl restart"
restart

will save the value of your $PATH, and prepend a project-specific directory to it. smartcd will automagically restore its old value when you leave the directory.

The second line creates a temporary alias which is probably something only meaningful to the directory you are in, allowing you to keep concise aliases that won't get in your way, and allow you to re-use them between projects.

And these commands are immediately available, as shown by the third line, which makes use of the newly defined alias to restart your server.

You could instead create the files non-interactively

echo 'autostash PATH=__PATH__/temporary/path:$PATH' | smartcd edit enter

which also highlights a convenient feature that replaces PATH with the directory name before the script is run.

If you like doing things by hand, you may prefer

mkdir -p ~/.smartcd/scripts/some/directory
echo 'autostash PATH=__PATH__/temporary/path:$PATH' >> ~/.smartcd/scripts/some/directory/bash_enter

HOW DOES IT WORK?

Scripts for smartcd are contained in a directory structure under your home, in the .smartcd directory. As you change directory, it will look for files which correspond to where you are leaving from and going to, and run them for you.

The primary way of doing this is to create a "cd" function which calls smartcd cd. This also works with push and popd. The simplest way to create these wrappers is to call smartcd setup cd, smartcd setup pushd, and smartcd setup pushd. When you smartcd config, this will be set up for you.

If you prefer (or in addition), you can hook the prompt command. This sets PROMPT_COMMAND in bash, or precmd in zsh. This is enabled using smartcd setup prompt-hook. After calling smartcd, it will call any prior command for those hooks. This feature allows users with the "autocd" option set in their shell to also benefit from smartcd.

The structure of .smartcd will mirror the filesystem hierarchy you wish to configure. For example:

  Path         Action      Script
------------------------------------------------------------
 /foo/bar       enter     ~/.smartcd/scripts/foo/bar/bash_enter
 /foo/bar/baz   leave     ~/.smartcd/scripts/foo/bar/baz/bash_leave

You can edit and read these files with the smartcd command using the "edit", "show", and "filename" actions.

user@host:/usr/local/bin$ smartcd filename enter
/home/user/.smartcd/scripts/usr/local/bin/bash_enter

user@host:/usr/local/bin$ smartcd show leave
/home/user/.smartcd/scripts/usr/local/bin/bash_leave does not exist

user@host:/usr/local/bin$ smartcd show enter
/home/user/.smartcd/scripts/usr/local/bin/bash_enter exists
-------------------------------------------------------------------------
smartcd inform "testing"
-------------------------------------------------------------------------

user@host:/usr/local/bin$ smartcd edit enter
--> edits ~/.smartcd/scripts/usr/local/bin/bash_enter

user@host:/usr/local/bin$ echo "some-command" | smartcd edit enter

One thing to note is that going from a directory to its child is not considered "leaving", so the bash_leave will not be run until you go to another directory that doesn't contain that same directory as part of its path. The scripts are run as appropriate if they exist for each level going back to the common element between the paths.

If you cd from /foo/bar/baz to /foo/quux/biff, the following actions would take place:

1) bash_leave for /foo/bar/baz
2) bash_leave for /foo/bar
3) bash_enter for /foo/quux
4) bash_enter for /foo/quux/biff

These scripts are run in the interactive shell using eval, so any variables or other environment effects will take place in the user's shell directly.

WHAT ARE SOME COMMON RECIPES?

Here are some examples of useful setups that have been created so far

DISPLAY A MESSAGE

Sometimes you may want a message to be shown when you enter or leave the directory, either to remind to you do something, or simply to let you know what the script has done.

You could use echo for this, but the issue with that is if you are doing something sophisticated with pipes, you may not want this message to interfere with the command being piped. For example, you might use the following command to copy some files

( cd foo; tar -cf - sub-dir ) | ( cd bar; tar -xf - )

but if "foo" has an enter script which echos something, this will corrupt the tar file. By using smartcd inform, this will suppress the output when it is detected that the output is not a terminal

smartcd inform "Reminder, don't forget to commit your code!"

PROMPT COLOR

If you want a visual cue that you need to be careful, it might make sense to change your prompt. Here's one that will temporarily make your prompt red while leaving its actual value alone.

autostash PS1='\[\e[1;31m\]'"$PS1"'\[\e[0m\]'

Note the double-quotes around $PS1. This is not superfluous, if your current value has any space characters in it, it's important to use quoting because otherwise it would be seen as a second argument to autostash

SCREEN

This one can be a bit tricky since screen commands from within screen tend to confuse it. And of course, creating a new screen window will execute your bash_enter scripts.

So what we'll do is set a variable in the attaching shell which is seen from within screen to prevent it from doing so.

if [[ -z $MYSCREEN ]]; then
    autostash MYSCREEN=1
    screen -c __PATH__/.screenrc -RRD my-special-screen-session
fi

PERLBREW

perlbrew is a system for installing multiple builds and versions of the Perl language, allowing you to easily switch between them. This is very valuable for development, but probably not what you want for your whole system.

smartcd now ships with a helper designed to integrate perlbrew and smartcd seamlessly together. Simply put this line in your enter script:

smartcd helper run perlbrew init /path/to/perlbrew/install

When you leave the directory, perlbrew will stop being in effect and you will get your previous perl back.

perlbrew is available at http://search.cpan.org/~gugod/App-perlbrew/

local::lib

Perl currently ships with a module named local::lib, which is handy for installing module dependencies outside of the standard install locations.

A helper is included for interacting with this module as well.

smartcd helper run perl-locallib activate __PATH__/perl5lib

If you want to explicitly remove a path (as you might do with -Mlocal::lib=--deactivate), this is supported

smartcd helper run perl-locallib deactivate __PATH__/perl5lib

but not required. If you don't perform this set, it will still be automatically cleared when you cd away restoring any prior local::lib or PERL5LIB state.

RVM

RVM is the Ruby Version Manager, which like perlbrew, can manage multiple versions of the language being installed at once. Because it too wants to wrap the cd command, things are a little tricker than with perlbrew. Fortunately, the RVM project has added express support for smartcd as the action taken during its own cd. If both projects are installed, RVM's cd() will call smartcd's, regardless of which order the two are set up.

RVM is available at http://beginrescueend.com/

STOP/START

If you want something to start running when you enter the directory, and stop running when you leave, you can certainly use smartcd for this. Here's an example of how someone is using smartcd to start and stop a Plack service

### enter script ###

# temporarily define the functions stop and start
autostash stop start pidfile="__PATH__/.pid"
start() {
    if [[ ! -f "$pidfile" ]] || ! kill -0 $(cat "$pidfile") >/dev/null 2>&1; then
        (
            builtin cd __PATH__/html
            plackup &> /dev/null &
            local pid=$!
            echo $pid > "$pidfile"
            smartcd inform "Started Plack with pid $pid"
        )
    fi
}
stop() {
    if [[ -f "$pidfile" ]] && kill -0 $(cat "$pidfile") >/dev/null 2>&1; then
        kill $(cat "$pidfile")
        rm "$pidfile"
    fi
}

# Create an alias that calls both functions
autostash alias restart="stop; sleep 2; start"

# And automatically start-up on enter
start


### leave script ###

# Shut down when leaving.  Yes, this function is still available here, and
# it will be removed by autounstash after this leave is complete
stop

# There are several things to make a note of here
#
#   1) The sub-shell created in the start() function is not actually necessary
#      if `start` is _only_ run from within smartcd, since the extra `cd` command
#      will not prevent you from ending up in the right directory.  However, since
#      this function can be called manually, it's safer to do this in a subshell.
#
#   2) I used `builtin cd` instead of just `cd` in start() to avoid smartcd being
#      called during another call, possibly causing surprising results.  However,
#      if you actually want smartcd to be run in that situation, it's ok to do so.
#
#   3) Use __PATH__ liberally to ensure that files and actions are taken in the
#      correct place, even after you've changed to a subdirectory of where the script
#      was defined.

and of course, if you want to be sure that this daemon is shut down properly if you simply log out or close your shell, you will want the exit hook as well

# in your .smartcd_config, see `smartcd config`
smartcd setup exit-hook

WHAT ELSE CAN IT DO?

HELPERS

A system for pre-written scripts is provided which implement things that you may find useful. This system allows people to distribute and share these independently of the core smartcd distribution.

Some helpers are provided with smartcd, including:

  • path:

    Simple ways to temporarily add elements to your PATH

    smartcd helper run path append __PATH__/bin
    smartcd helper run path prepend __PATH__/bin
    
  • history:

    This keeps commands run in the current and any subdirectories in a separate history file specified as an argument. The also-read command will prepend another history file into the shell's buffer when setting up, so that other history can be availble "further back" in your history.

    smartcd helper run history also-read ~/.bash_history
    smartcd helper run history localize __PATH__/.history
    

    You can also have ask it to save and/or reload this history file on each prompt

    smartcd helper run history prompt-append
    smartcd helper run history prompt-reload
    
  • perlbrew:

    Automagic setup and teardown of Perlbrew

    smartcd helper run perlbrew init /path/to/perlbrew/install
    

TEMPLATES

In addition to configuring scripts individually, smartcd supports a template system, which can be set up to re-use common configuration among many directories. This is controlled with the "smartcd template" action.

To create a new template based on the current directory, run:

smartcd template create some_template_name

This will create a new template named "some_template_name", and prepopulate it from the bash_enter and bash_leave files corresponding to the working directory, replacing any instance of your working directory with PATH.

You can then edit the contents with smartcd template edit some_template_name. The create step is optional, and if you edit a template that is not yet created you will start with an empty one.

Now that your template is ready, you'll want to use it somewhere. For this, there are two options:

  1. Run it "in-place", and all changes to the template will be dynamically picked up by the enter and exit scripts which execute it

      echo 'smartcd template run some_template_name' | smartcd edit enter
    

    The run action will determine if you are in an "enter" or "leave" script, and execute the correct portion of the template. This does not need to be the only line in your script, and in fact you can even run more than one template from the same script.

  2. Copy the current contents of the template to the scripts for a directory, as a one-time operation. This will not automatically propagate changes to the places it is in use, and can be used as a way to quickly bootstrap scripts but allow them to exist independently.

      smartcd template install some_template_name
    

    The other template editor actions are show, list, and delete.

NESTABLE PROMPT COMMANDS

Users can define their own actions which will be taken just before each prompt is displayed. In fact, smartcd itself can use this mechanism to invoke itself.

smartcd on-prompt takes this concept to a new level. By specifying commands to be run, they will be run on each prompt, similar to the built-in feature, but only while you are in the current directory and its children. In addition to this, further on-prompt commands specified in child directories will run in addition to the current ones rather than replacing them.

For example:

~/foo$ smartcd on-prompt 'echo test 1'
test 1
~/foo$ cd bar
test 1
~/foo/bar$ smartcd on-prompt 'echo test 2'
test 1
test 2
~/foo/bar$ cd ..
test 1
~/foo$ cd
~$

EXIT HOOK

By default, your enter scripts will be run when a shell is started. However, the opposite is not the case. If you'd like your leave scripts to run when the shell exits, smartcd is able to utilize the shell's EXIT trap hook to do so, or in zsh, the zshexit hook. This is enabled by running

smartcd setup exit-hook

BACKUP

If you would like to back up your scripts and templates, or copy them to another computer, you can use the provided export/import feature.

# Export your scripts
smartcd export > my_smartcd_backup

# Several methods to import them
smartcd import my_smartcd_backup
cat my_smartcd_backup | smartcd import

For more complete documentation, see the documentation in lib/core/smartcd.

OTHER LIBRARIES

VARSTASH

As already discussed, the included library lib/core/varstash provides several functions for saving values to a temporary location so that you can edit them, and then later restore the original value.

In addition to autostash, you could manually stash and unstash using functions with those names if there is some need to do so

echo 'stash FOO=bar' | smartcd edit enter
echo 'unstash FOO' | smartcd edit leave

You may also trigger autostash's restore mechanism by calling

autounstash

by hand. It's safe to do so multiple times and it won't harm smartcd if you do this.

If you run stash, unstash, or autostash interactively, they will instruct you on how to create files for smartcd to run those commands for you. If you do not wish to see this advice, set VARSTASH_QUIET=1. The library can automatically follow its own advice and configure these files if you set VARSTASH_AUTOCONFIG=1. It can do so, but also give you an opportunity to make additional edits to the relevant file, if you set VARSTASH_AUTOEDIT=1.

Alias stashing was briefly mentioned, and it is supported to do in-line stashing and declaration of an alias with autostash

autostash alias mycmd="do something crazy"

However, stashing functions looks like this:

autostash my_func
my_func() {
    some_new_definition
}

It's useful to autostash something even before it's set, because that triggers the mechanism which will unset them upon leaving. Since functions cannot be declared inline with autostash, this is how you should do it.

ARRAYS

Bash added array support in version 2.0, but it doesn't have a very good set of supporting built-ins. In particular, I find myself missing the Perl functions push, pop, shift, unshift, reverse.

To provide these capabilities, another library, lib/core/arrays, is included. The provided functions are:

apush    - Add an element to the end of your array
apop     - Remove the last element from the array and print it
ashift   - Remove the first element from the array and print it
aunshift - Add an element to the beginning of the array
areverse - Reverse the order of elements in the array
afirst   - Like ashift, but doesn't remove anything.
alast    - Like apop, but doesn't remove anything.
anth     - Retreive the n-th element of an array.
alen     - Print the current number of elements in the array
acopy    - Copy an array into a new variable

See documentation included in lib/core/arrays for more detail.

LICENSE

This code is Copyright (c) 2009,2012 Dave Olszewski cxreg@pobox.com

You may distribute under the terms of either the GNU General Public License v2 or the Artistic License.

SEE ALSO

As with most ideas worth doing, there are other implementations of some of the things provided by smartcd. Here are a few of them, and how they differ from this library.

  • ondir - http://swapoff.org/ondir.html

    • Written in C, and is executed by a "cd" function
    • Requires manual and explicit variable setting and unsetting
  • direnv - https://github.com/zimbatm/direnv/

    • Requires ruby
    • Works only with PROMPT_COMMAND or precmd
    • Does not walk directory hierarchy
    • Does not support functions or aliases
    • Is entirely "snapshot" based
    • Runs files directly out of local directory, similar to "legacy mode"
  • EnvWatcher - https://github.com/MrMasterplan/EnvWatcher

    • Requires python
    • Only supports bash
    • Is triggered manually, not automatically
    • Does not walk directory hierarchy
    • Is entirely "snapshot" based
    • Does not allow other actions besides environment variable switching
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