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+---
+
+title: Useful Bash variables
+
+date: 2020-11-12
+
+layout: post
+
+lang: en
+
+ref: useful-bash-variables
+
+---
+
+[GNU Bash][gnu-bash] has a few two letter variables that may be useful when
+typing on the terminal.
+
+[gnu-bash]: https://www.gnu.org/software/bash/
+
+## `!!`: the text of the last command
+
+The [`!!` variable][previous-command] refers to the previous command, and I find
+useful when following chains for symlinks:
+
+[previous-command]: https://www.gnu.org/software/bash/manual/bash.html#Event-Designators
+
+```shell
+$ which git
+/run/current-system/sw/bin/git
+$ readlink $(!!)
+readlink $(which git)
+/nix/store/5bgr1xpm4m0r72h9049jbbhagxdyrnyb-git-2.28.0/bin/git
+```
+
+It is also useful when you forget to prefix `sudo` to a command that requires
+it:
+
+```shell
+$ requires-sudo.sh
+requires-sudo.sh: Permission denied
+$ sudo !!
+sudo ./requires-sudo.sh
+# all good
+```
+
+Bash prints the command expansion before executing it, so it is better for you
+to follow along what it is doing.
+
+## `$_`: most recent parameter
+
+The [`$_` variable][recent-parameter] will give you the most recent parameter
+you provided to a previous argument, which can save you typing sometimes:
+
+```shell
+# instead of...
+$ mkdir -p a/b/c/d/
+$ cd a/b/c/d/
+
+# ...you can:
+$ mkdir -p a/b/c/d/
+$ cd $_
+```
+
+[recent-parameter]: https://www.gnu.org/software/bash/manual/bash.html#Special-Parameters
+
+## Conclusion
+
+I wouldn't use those in a script, as it would make the script terser to read, I
+find those useful shortcut that are handy when writing at the interactive
+terminal.