Nire Bryce

@NireBryce

reality is the battlefield

she/they (pl)
breadthcharge.net/

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🐥 I am not embroiled in any legal battle
🐦 other than battles that are legal 🎮

I speak to the universe and it speaks back, in it's own way.

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email: contact at breadthcharge dot net

I live on the northeast coast of the US.

'non-functional programmer'. 'far left'.

conceptual midwife.

https://cohost.org/NireBryce/post/4929459-here-s-my-five-minut

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Nire Bryce @NireBryce9/11/2023, 8:56 PM

TIL by forgetting the [[, negating a statement in a bash `if` statement evaluates the negated, it doesn't negate the output

which makes sense but the lack of any sort of separation sorta makes it unclear which part it'd negate. that's fine, tho.

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in reply to @NireBryce's post:

sage @wavebeem9/11/2023, 9:54 PM

can you explain this in more detail?

my understanding was that it just inverts the condition so exit code 0 fails the if statement (and the rest of the line is just a regular command rather than the bash special syntax [[

Nire Bryce @NireBryce9/11/2023, 10:07 PM

if ! statement; then
    echo "if"
else
     echo "else"

yields the else, because it parses ! statement as going into the if

I've literally never used them without the brackets outside of forgetting so i didn't realize

sage @wavebeem9/11/2023, 10:52 PM

yeahh... my understanding is that [ is potentially just a regular program called test normally... but then [[ is bash-specific non-POSIX shell level syntax that fixes some of the issues related to variable expansion and whatnot

it took me a while to sort out regular if vs if [ vs if [[ in bash x_x;

Nire Bryce @NireBryce9/11/2023, 11:21 PM

right, but if you flub the negation and put it outside of [/[[, it still will do what I'm saying, which is what tripped me up

whereas in other languages, in this example python but also most others,

if not <thing>: 
    print("if") 
else: 
    print("else")

will print "if" and not "else"

sage @wavebeem9/12/2023, 1:19 AM

bash: if [[ ! "$x" = "" ]]; then echo T; else echo F; fi
T

bash: if ! [[ "$x" = "" ]]; then echo T; else echo F; fi
T

bash: if [[ "$x" != "" ]]; then echo T; else echo F; fi
T

bash: if ! [[ "$x" = "" || "$x" = "1" ]]; then echo T; else echo F; fi
F

bash: if [[ ! "$x" = "" || "$x" = "1" ]]; then echo T; else echo F; fi
T

>>> (not x == 0 or x == 1)
True

>>> not (x == 0 or x == 1)
False

>>> not x == 0
True

>>> not (x == 0)
True

>>> x != 0
True

it seems like it matches up to me with python, maybe i'm missing something 😅

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