Pure Sh Bible

Post by hddqsb » Tue, May 02, 2023, 1:24 PM UTC

koolba wrote: post #75

ndsipa_pomu wrote: post #12

Earlier quoted context omitted.

It's well worth learning to use printf instead of echo to avoid all the various ways that echo can break or is not well defined. https://mywiki.wooledge.org/BashPitfalls#echo_.24foo

The %q format alone justifies learning about printf. Vanilla echo is for chumps.

Post by hddqsb » Tue, May 02, 2023, 1:47 PM UTC

1letterunixname wrote: post #77

cduzz wrote: post #7

I have to take exception to some of this; it's "technically correct" but like much of shell, likely full of terrifying edge cases that are best avoided. For instance, using eval to have variables with variable names is madness. $ var="world" $ eval "hello_$var=value" $ eval printf '%s\n' "\$hello_$var" I suppose the fancy business with printf is flexing, but I suspect the majority of people scanning documents like th…

I'm scratching my head at most of it and there's large portions that are incomplete or trivial. bash is ubiquitous. If you're trying to develop an entire web framework to run on a Bourne shell from busybox, dash, or FreeBSD 4, there's probably a better way to do it. Use the tool you have, not a hypothetical one compatible with 1983. YAGNI. Here's a common pattern for appending to PATH system-wide once: # /etc/profile…

    prepend() {
        local val
        eval "val=\$$1"
        export "$1=$2${val:+${3-:}$val}"
    }

    append() {
        local val
        eval "val=\$$1"
        export "$1=${val:+$val${3-:}}$2"
    }

Post by hddqsb » Tue, May 02, 2023, 2:31 PM UTC

protomikron wrote: post #98

tlamponi wrote: post #92

Earlier quoted context omitted.

> where things get easier if you just switch to a language with less caveats (like Python). For general, non-domain specific things, it gets IMO easier by two main reasons 1) obviously when using tools where one has more experience with, but 2) also when the tool is more widely available, and POSIX shell is probably one of the most (by default) available interpreters with a somewhat human-friendly input mode there is…

> They use the printf "%f" float format conversion so `printf "%f" 2e3` will work just fine, whereas using something that definitively is not a float makes printf exit with an error code as it fails to format the value as float, failing this check. You are of course correct (sorry to sound like a language model), I missed the printf.

Post by hddqsb » Tue, May 02, 2023, 2:54 PM UTC

teddyh wrote: post #57

tpoacher wrote: post #33

Regarding conditional expressions: I found something neat recently. The coreutils version of `test` doesn't have this, and when you use `test`, typically what you're using is the coreutils one. But if you use `builtin test` to force the bash builtin variant of `test`, this has a nice `-v` switch, which allows you to check if a variable is set. I found out about this recently when I had to use it in my bash argument p…

If you already assume bash, then you don’t need the “-v” option to the “test” builtin; just do if [ "${foo+some_string}" = "" ]; then echo "foo is unset" fi or, in your case: if test "${2+x}" = "" # i.e. if $2 is not set

Post by hddqsb » Tue, May 02, 2023, 4:33 PM UTC

hddqsb wrote: post #124

1letterunixname wrote: post #77

Earlier quoted context omitted.

I'm scratching my head at most of it and there's large portions that are incomplete or trivial. bash is ubiquitous. If you're trying to develop an entire web framework to run on a Bourne shell from busybox, dash, or FreeBSD 4, there's probably a better way to do it. Use the tool you have, not a hypothetical one compatible with 1983. YAGNI. Here's a common pattern for appending to PATH system-wide once: # /etc/profile…

Your "zsh/bash" code doesn't actually use any zsh/bash-only features, so it is compatible with POSIX sh. But you have a quoting bug: you should escape the `$` in `$2` and `${3...}` to protect from double-eval. I'd personally try to minimise the use of eval, e.g. prepend() { local val eval "val=\$$1" export "$1=$2${val:+${3-:}$val}" } append() { local val eval "val=\$$1" export "$1=${val:+$val${3-:}}$2" }