WEBVTT captioned by howard
NOTE Introduction
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I have 10 minutes to talk you into
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giving Eshell a second chance.
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Have the right perspective and expectation,
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and I think you’ll really enjoy it.
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Just remember eshell is a shell,
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not a terminal emulator.
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I use both Eshell and vterm.
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I’m going to talk and type fast,
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as I have 10 reasons for you to try Eshell again.
NOTE 1. It’s an Emacs REPL
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1. It’s an Emacs REPL.
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I mean, check this out.
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Let’s start up Eshell here.
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Let’s just type a Lisp expression.
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It works.
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As a shell, the parens are kinda optional.
NOTE 2. It’s also a shell
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2. It’s also a shell.
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While eshell may look like a shell, like Bash
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you should view it as a REPL
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with parenthesis-less s-expressions.
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This makes sense, because a shell command with options,
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like this ls command,
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looks like an s-expression.
NOTE 3. You can mix these two modes
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3. You can mix these two modes.
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Shells can call subshells
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which return their output like a function call,
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like this Bash command.
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In this Eshell example,
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I use the output of a text file
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as command line arguments to ripgrep.
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Notice how I use braces
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to state that it is a call to an eshell expression.
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We can mix Lisp-expressions and Shell-expressions.
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Allow me a contrived example.
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Notice I use good ol' setq to create a variable.
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Yes, those are global Emacs variables available everywhere.
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In Eshell, the wildcard actually creates a list.
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This variable assignment doesn’t work as you might expect,
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as setq in Eshell is still setq,
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and it assigns variables in pairs.
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To make a list in Eshell, we use listify:
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Without parens, Eshell is in “shell mode”,
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which means that words are strings,
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and variables need to be prefixed with dollar signs.
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A command can have both Eshell and Lisp expressions.
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As you can see here,
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I have a call to ripgrep,
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but part of it is an s-expression.
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Remember the differences:
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With parens, eshell treats it as Lisp,
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like the last line in my example.
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With braces, eshell follows these shell-like rules:
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First, if it looks like a number, it's a number.
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Otherwise, eshell converts it to a string
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(quotes, like a shell, groups words).
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What about this mix between functions and executables
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for the first word?
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Functions that begin with eshell are called first.
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Next in priority are executables on your $PATH,
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then matching Lisp functions.
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You can actually switch this order
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with the `eshell-prefer-lisp-functions` variable.
NOTE 4. Emacs is better than shell
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4. Emacs is actually better than shell.
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If the following works, why would you call
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expr or bc or dc, or any of those other calculators?
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You can just call a Lisp expression.
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Why call less or more when you could call view-file?
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Here, I’ve aliased less to view-file.
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Load it up, and it shows up in an Emacs mode.
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Just like with less, if you hit q,
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you go back to your Eshell terminal.
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I do have an improvement, though.
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The problem with view-file is
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it takes a single file as an argument.
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In a shell, we might want to view more than one.
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So let’s make a solution to that.
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This function will call the first function
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with the first argument,
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and the second function with each of the rest.
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This allows me to make a version of less
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that calls view-file on the first [argument] given,
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but open in another window for each additional file.
NOTE 5. Better regular expressions
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5. Better regular expressions.
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Can’t remember regular expressions when calling
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grep or some other search function? Use the rx macro.
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Here I call ripgrep again, but this time,
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I’m using a Lisp expression calling the rx macro
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to look for UUIDs in the files in my current directory.
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But I have another improvement for this.
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While the rx macro is freaking cool for Emacs Lisp,
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it doesn’t always translate to regular expressions
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accepted by most commands.
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The (I have no idea how to pronounce this) pcre2el project
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can convert from a Lisp regular expression
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to Perl-compatible regular expressions (PCRE)
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acceptable by most search commands.
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I’ve created a new macro here, prx,
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that translates the output of the rx macro.
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This allows me to type something much more readable,
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and probably easier to remember.
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Certainly easier than this freaking regular expression.
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I’ve got an even better improvement.
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The rx macro with regular expression snippets
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can be assigned to key words
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that I can then take advantage of.
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Now our command would be much simpler to type.
NOTE 6. Loops are better with predicates
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6. Loops are better with predicates.
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Let’s say you want to remove the execute bit
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from files that have it.
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In a shell like bash, you need both a for loop and an if,
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as you can see in this example.
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With eshell, use a predicate to combine into a simple loop.
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The paren x after a file glob
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filters for only files marked as executable.
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Now here is another improvement.
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Since we often type loops to execute on one command,
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what about creating a function
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that can do this all in one go?
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This do function splits the arguments on that double colon,
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where the left side is a single statement to run,
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and the right side is a list of files.
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I have to append and flatten it
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in order for it to work.
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It loops through each file,
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creating an eshell command with the file appended.
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With this, I can remove the execute bit
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on all CSV files that have it.
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I see that my example wasn’t too good, as most commands
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like chmod accept multiple files, but you get the idea.
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In my final, larger form on my website,
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I don’t assume the command expression accepts
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a file as a final argument,
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as I can also replace underscores with the filename.
NOTE 7. Output of last command
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7. Output of last command.
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Most shells have a special variable
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like $? for the exit code of the last command.
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While reading through the source code,
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I noticed that the $$ refers to
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the output of the last command.
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This seems pretty cool.
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However, Eshell returns true or nil
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when running external commands,
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so accessing the output from a call to ls
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doesn’t work as expected.
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But this is Emacs.
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We can fix that.
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After running any command, eshell sets these four variables.
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I can hook a function call after every Eshell command.
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Using buffer-substring,
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I store the output into a global variable,
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and extend Eshell’s special variables list.
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In my Emacs configuration,
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I turned this variable into a ring,
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so while $$ works,
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so does array sub-scripting on that variable.
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This allows me to run a command
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and use the output from that command more than once.
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The code for this is a bit longer,
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so you’ll need to see my Emacs configuration for details.
NOTE 8. Redirection back to Emacs
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8. Redirection back to Emacs.
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Output of any command
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can go to kill-ring (or the clipboard).
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Think of the implications.
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You don’t have to go into text selection mode.
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Just grab the output.
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In fact, with our $$ improvement,
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we can always copy the output from the last command
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to the clipboard.
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Better yet, let’s write the output
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to our engineering notebook.
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Here’s my idea.
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First, create a capture template that takes a string,
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or if called interactively, the region,
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and that does an immediate-finish after inserting
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that string to the default notes file.
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Next, create a wrapper function
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to call org-capture-string to run that template.
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Finally, we add our new function to eshell-virtual-targets.
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Let’s see this in action.
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I have a CSV file of user information.
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I can use grep and cut to extract some of that
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and write it out to this month’s engineering notebook.
NOTE 9. Using Emacs buffers
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9. Using Emacs buffers.
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Why leave the results of eshell commands
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in the *eshell* buffer?
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Send the output into a buffer where you can use it.
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Here’s a call to ripgrep
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that searches for lines with email addresses
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using a complicated regular expression
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that I added to my prx macro.
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When I switch to this almost-grep buffer,
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I can turn on grep-mode.
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Now I can jump around as if I just called grep directly.
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Perhaps I’m proficient with my prx macro
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to filter out entries,
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but not good with shell commands
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that I can use in pipes to extract just one…
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the address column, for instance?
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Let’s just extract it,
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send it to a buffer called email-list,
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and now I can use Emacs commands that I know and love
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to edit the data directly.
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We currently have an over-sight
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that the Eshell’s built-in cat command
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doesn’t pipe buffer contents as standard in.
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So I created a bcat, a buffer cat, function to do this.
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So this command works
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to grab my email addresses I just extracted
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and send them to another program.
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If you’re interested, I have a more elaborate
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and yet simpler workflow surrounding sending data
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back and forth from Eshell to Emacs buffers.
NOTE 10. cd to remote systems
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10. Did I mention that you can cd to remote systems?
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This command uses SSH to jump to my host, goblin,
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start a root session, and jump to the etc directory.
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Remember that Tramp can be finicky
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if you start blinging your remote hosts with oh-my-zshell,
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and funky prompts and things like that,
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so your mileage may vary.
NOTE Summary
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In summary: Use eshell if you want
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a quick way to run commands and Emacs functions as a REPL,
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or to run an OS program but process the output with Emacs.
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Keep in mind that Eshell has two types of subshells,
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and you can mix and match during a command call.
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The rx macro is really cool.
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Eshell loops are better with filters and predicates …
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if you can remember them.
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Take advantage of Emacs buffers
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to really enhance your shell experience.
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You’ve now seen that just like Emacs,
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I’ve crafted Eshell to be my own shell creation,
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tailored to my workflow.
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So, steal my spells, cast your own magic,
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but feel free to share your incantations back to me.
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I’ve gone over my time allotment, so we’ll have to
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continue this discussion on the intertubes.
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Why yes, I have joined the birdless diaspora,
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so toot me over there.
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Thanks.
