izabera

import collections
import itertools
import signal
import os
import time
import errno

blocks = " ▁▂▃▄▅▆▇█"

izabera

you know ${var?error message here} in sh? it produces an error and prints the message if $var is undefined. otherwise it expands to $var

introducing: ${var+${error message here}}

if $var is defined, the spaces in the error message cause a syntax error, which prints the message. otherwise it expands to nothing

(and similarly for all other outer expansions)

it reliably[^reliable] works[^works] perfectly[^dashzsh] in every[^shells] posix sh[^ext]

izabera

#!/bin/bash

# basic bash game loop

shopt -s extglob globasciiranges
gamesetup () {
    exitfunc() { :; } # override this if you want something done at exit
    trap exitfunc exit
    if [[ -t 1 ]]; then
        printf '\e[?%s' 1049h 25l

izabera

context: shells want to leave the seek position at the right offset so external commands can continue reading from the same fd

---

i saw this somewhat surprising tally of syscalls in bash. let's investigate

one iteration:

• unblock all signals

izabera

.globl _start
_start:
dec %ecx    # comment this out for a 6 byte binary that takes ~1090 years :)
loop:
loop loop
mov $60, %al
syscall

izabera

$ clang++ operator_symbols.cpp -c -std=c++23 -pedantic -Wall -Wextra 
$ nm -C operator_symbols.o | grep meow
0000000000000000 T operator"" _meow(char const*)
0000000000000000 W meow::promise_type::final_suspend()
0000000000000000 W meow::promise_type::initial_suspend()
0000000000000000 W meow::promise_type::get_return_object()
0000000000000000 W meow::operator&&(int)
0000000000000000 W meow::operator&()
0000000000000000 W meow::operator&(int)
0000000000000000 W meow::operator&=(int)

izabera

#include <string>
#include <unordered_map>
#include <variant>

template <typename keytype = std::string, typename valtype = std::string>
struct autovivi {
    using maptype = std::unordered_map<keytype, autovivi>;
    std::variant<std::monostate, valtype, maptype> valueormap;

    autovivi() = default;

izabera

A funky shell thingy that I've never seen before

So you're in posix sh and you want to do the equivalent of this in bash:

foo | tee >(bar) >(baz) >/dev/null

(Suppose that bar and baz don't produce output. Add redirections where needed if that's not the case.)

izabera

#!/bin/sed -f

# store rule in hold space
1 { h; d; }

# make borders wrap
s/\(.\)\(.*\)\(.\)/>\3\1\2\3\1|/

# do some mucking around that can probably be done more elegantly by someone who is actually good at sed
x; G; h; s/\n.*//; x

izabera

#!/bin/sh -e
target=${1?usage: $0 pid [fd]}
fd=${2-1}
fifo=fifo.$$
log=log.$$

mkfifo $fifo
echo writing to $log
tee $log <$fifo >/proc/$target/fd/$fd &