What's dt? ⌾
dt is a functional programming riff on shell one-liners. It's useful for many situations, its simple syntax makes it easy to write and read, and dt is for solving problems with no pretense of elegance. The philosophy can be summed up with quotes from the ultimate handyman, Red Green:
- If it ain't broke, you're not trying.
- ...the handyman's secret weapon, duct tape.
- This is only temporary, unless it works.
- Spare the duct tape, spoil the job.
It's meant to supplement (not replace!) other tools like awk, sed, xargs, and shell built-ins. A functional programming riff on Python/Ruby/Perl one-liners, with extremely minimal syntax that's easy to read and easy to reason about.
dt is released as open source software, usable under the (permissive) terms of the BSD 3-Clause license.
Use in Pipes ⌾
When piping in/out, the REPL is skipped. If dt has receives standard input from a pipe, it's fed to `dt` as a list of lines.
$ seq 3 | dt rev pls
3
2
1
Great for aliases:
$ alias scream-lines="dt [upcase words unlines] map pls"
$ echo "hey you pikachu" | scream-lines
HEY
YOU
PIKACHU
If you want to read lines manually, use `stream` as the first command:
$ alias head.dt="dt stream [rl pl] args last to-int times"
$ seq 100 | head.dt 3
1
2
3
Use in Shebang Scripts ⌾
When the first argument to `dt` is a file starting with `#!` it will interpret the file. In short: `dt` supports shebang scripting.
A naive tee implementation:
tee.dt
#!/usr/bin/env dt
readln unlines \stdin :
args pop \file :
stdin pl
stdin file writef
Then use like:
cat wish-list | sed 's/red/green/g' | tee.dt new-wish-list
Using Interactive Mode (REPL) ⌾
Running `dt` by itself with no pipes in or out starts a read-eval-print loop (REPL).
$ dt
dt 1.x.x
Now, this is only temporary... unless it works.
» # Comments start with #
»
» 1 1 + println
2
»
» # Printing is common, so there are a bunch of printing shorthands.
» # "p" is print, "pl" is print line, "pls" is print lines (i.e. of a list of values)
» # Let's define a command that consumes a value, prints it, then returns its double.
»
» [ \n : n p " " p n 2 *] \print-and-double def
»
»
» # And let's do it... 7 times!
»
» 1 \print-and-double 7 times drop
1 2 4 8 16 32 64
»
»
» # You can conditionally execute code
»
» ["hi" pl] false do?
» ["bye" pl] true do?
bye
»
» quit
For a better experience, also install rlwrap and set a shell alias like so:
$ alias dtsh='rlwrap dt'
$ dtsh
dt 1.x.x
Now, this is only temporary... unless it works.
»
The above example assumes a bash-like shell. Details on the syntax and configuration files to set an alias that persists will vary by your shell.
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