186 lines
7 KiB
Markdown
186 lines
7 KiB
Markdown
---
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title: "Alternate Files"
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permalink: /docs/alternates
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---
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When possible, it is best to use the same files across all systems. However,
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there are occasions when you need different files in some places. Below are
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features and strategies for dealing with those occasions.
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## Symlink alternates
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It can be useful to have an automated way of choosing an alternate version of a
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file for a different operating system, host, user, etc.
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yadm will automatically create a symbolic link to the appropriate version of a
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file, when a valid suffix is appended to the filename. The suffix contains the
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conditions that must be met for that file to be used.
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The suffix begins with `##`, followed by any number of conditions separated by
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commas.
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##<condition>[,<condition>,…]
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Each condition is an attribute/value pair, separated by a period. Some
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conditions do not require a "value", and in that case, the period and value can
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be omitted. Most attributes can be abbreviated as a single letter.
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| Attribute | Meaning |
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| - | - |
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| `template`, `t` | Valid when the value matches a supported template processor. See the [Templates](/docs/templates) section for more details.|
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| `user`, `u` | Valid if the value matches the current user. Current user is calculated by running <code>id ‑u ‑n</code>. |
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| `distro`, `d` | Valid if the value matches the distro. Distro is calculated by running <code>lsb_release ‑si</code> or inspecting <code>/etc/os-release</code> |
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| `os`, `o` | Valid if the value matches the OS. OS is calculated by running <code>uname ‑s</code>. <sup>*</sup> |
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| `class`, `c` | Valid if the value matches the local.class configuration. Class must be manually set using <code>yadm config local.class <class></code>. |
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|`hostname`, `h`|Valid if the value matches the short hostname. Hostname is calculated by running `hostname`, and trimming off any domain.|
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|`default`|Valid when no other alternate is valid.|
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<sub><sup>*
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The OS for "Windows Subsystem for Linux" is reported as "WSL", even though uname identifies as "Linux".
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<br/>
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*
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If `lsb_release` is not available, "distro" will be the ID specified in `/etc/os-release`.
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</sup></sub>
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You may use any number of conditions, in any order. An alternate will only be
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used if _ALL_ conditions are valid. For all files managed by yadm's repository
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or listed in `$HOME/.config/yadm/encrypt`, if they match this naming convention,
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symbolic links will be created for the most appropriate version.
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The "most appropriate" version is determined by calculating a score for each
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version of a file. A [template](/docs/templates) is always scored higher than
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any symlink condition. The number of conditions is the next largest factor in
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scoring. Files with more conditions will always be favored. Any invalid
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condition will disqualify that file completely.
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If you don't care to have all versions of alternates stored in the same
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directory as the generated symlink, you can place them in the
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`$HOME/.config/yadm/alt` directory. The generated symlink or processed template
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will be created using the same relative path.
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Alternate linking may best be demonstrated by example. Assume the following
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files are managed by yadm's repository:
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$HOME/path/example.txt##default
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$HOME/path/example.txt##class.Work
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$HOME/path/example.txt##os.Darwin
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$HOME/path/example.txt##os.Darwin,hostname.host1
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$HOME/path/example.txt##os.Darwin,hostname.host2
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$HOME/path/example.txt##os.Linux
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$HOME/path/example.txt##os.Linux,hostname.host1
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$HOME/path/example.txt##os.Linux,hostname.host2
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If running on a Macbook named `host2`, yadm will create a symbolic link which looks like this:
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`$HOME/path/example.txt` → `$HOME/path/example.txt##os.Darwin,hostname.host2`
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However, on another Mackbook named `host3`, yadm will create a symbolic link which looks like this:
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`$HOME/path/example.txt` → `$HOME/path/example.txt##os.Darwin`
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Since the hostname doesn't match any of the managed files, the more generic
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version is chosen. If running on a Linux server named `host4`, the link will be:
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`$HOME/path/example.txt` → `$HOME/path/example.txt##os.Linux`
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If running on a Solaris server, the link will use the default version:
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`$HOME/path/example.txt` → `$HOME/path/example.txt##default`
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If running on a system, with class set to `Work`, the link will be:
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`$HOME/path/example.txt` → `$HOME/path/example.txt##class.Work`
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If no `##default` version exists and no files have valid conditions, then no
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link will be created.
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Links are also created for directories named this way, as long as they have at
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least one yadm managed file within them.
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yadm will automatically create these links by default. This can be disabled
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using the `yadm.auto-alt` configuration. Even if disabled, links can be manually
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created by running `yadm alt`.
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## Class and Overrides
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Class is a special value which is stored locally on each host (inside the local
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repository). To use alternate symlinks using `##class.<CLASS>`, you must set the
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value of class using the configuration `local.class`. This is set like any other
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yadm configuration—with the `yadm config` command. The following sets the
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`local.class` to be "Work".
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yadm config local.class Work
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Similarly, the values of `os`, `hostname`, and `user` can be manually overridden
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using the configuration options `local.os`, `local.hostname`, and `local.user`.
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## Templates
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Templates are another powerful tool for creating alternate content on each host.
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See the [Templates](/docs/templates) documentation for full details.
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## Strategies for alternate files on different systems
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Where possible, you should try to use the same file on every system. Here are a few examples:
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### .vimrc
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```vim
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let OS=substitute(system('uname -s'),"\n","","")
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if (OS == "Darwin")
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" do something that only makes sense on a Mac
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endif
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```
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### .tmux.conf
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# use reattach-to-user-namespace as the default command on OSX
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if-shell "test -f /usr/local/bin/reattach-to-user-namespace" 'set -g default-command "reattach-to-user-namespace -l bash"'
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### .bash_profile
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```bash
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system_type=$(uname -s)
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if [ "$system_type" = "Darwin" ]; then
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eval $(gdircolors $HOME/.dir_colors)
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else
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eval $(dircolors -b $HOME/.dir_colors)
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fi
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```
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### .gitconfig
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However, sometimes the type of file you are using doesn't allow for this type of
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logic. If a configuration can do an "_include_", you can include a specific
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alternate version using yadm. Consider these three files:
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`.gitconfig`
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```ini
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[log]
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decorate = short
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abbrevCommit = true
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[include]
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path = .gitconfig.local
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```
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`.gitconfig.local##os.Darwin`
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```ini
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[user]
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name = Tim Byrne
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email = tim@personal.email.org
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```
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`.gitconfig.local##os.Linux`
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```ini
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[user]
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name = Dr. Tim Byrne
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email = dr.byrne@work.email.com
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```
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Configuring Git this way includes `.gitconfig.local` in the standard
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`.gitconfig`. yadm will automatically link the correct version based on the
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operating system. The bulk of your configurations can go in a single file, and
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you just put the exceptions in OS-specific files.
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