GETFLAGS(1plan9)

💖 GETFLAGS 💖

okay bestie, listen up — this is a plan9 section 1 situation, and we're talking about command-line parsing for shell scripts. two lil utilities: getflags and usage. they are the dynamic duo of not letting your script choke on -x and friends. periodt. 🎀

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✨ SYNOPSIS ✨

getflags $*

usage [ progname ]

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🦋 DESCRIPTION 🦋

💅 getflags

so getflags looks at the options in its command-line arguments and parses them according to the environment variable $flagfmt. it's giving "i read the rules and i follow them". 👑

$flagfmt needs to be a list of comma-separated options. and each option is one of two vibes:

• a single letter — meaning it does not take arguments
• a letter followed by the space-separated names of its arguments

then getflags prints an rc(1) script on standard output, and that script initializes the environment variable $flagx for every option mentioned in $flagfmt. every single one. no option left behind fr fr.

here's the tea on what that script does per option:

• if the option is not present on the command line → the script sets that option's flag variable to an empty list
• if the option is present → the script sets that option's flag variable to a list containing the option's arguments... or, if the option takes no arguments, to the string 1. slay.

and the script also sets the variable $* to the list of arguments that come after the options. ✨

the final line of the script sets the $status variable:

• empty string on success 💖
• the string usage when there's an error parsing the command line 💀

🌸 usage

usage prints a usage message to standard error. dramatic? maybe. necessary? absolutely.

it builds that message out of:

• $flagfmt, as described above 👆
• $args, which should contain the string to be printed explaining non-option arguments
• $0, the program name (see rc(1))

⚠️ important bestie: if you're running under sh(1), which does not set $0, then you have to give the program name explicitly on the command line. no shortcuts, no vibes, just type it. 😭

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🌈 EXAMPLE 🌈

let's parse the arguments for leak(1) — iconic behavior honestly:

flagfmt='b,s,f binary,r res,x width'
args='name | pid list'
if(! ifs=() eval `{getflags $*} || ~ $#* 0){
     usage
     exit usage
}

see how $flagfmt and $args are just... sitting there, being set, doing their thing? that's the whole mood. 💜

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🍓 SOURCE 🍓

/src/cmd/getflags.c
/src/cmd/usage.c

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👑 SEE ALSO 👑

• arg(3)

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okay that's the whole page, you ate it, you understood it, you're a shell-scripting main character now 💅✨ this was GETFLAGS(1plan9) from the plan9 manual, section 1 — go forth and parse responsibly, bestie 🫶🌸