88 lines
1.7 KiB
Markdown
88 lines
1.7 KiB
Markdown
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---
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title: The Beautiful in the Ugly
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date: 2018-04-23
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for: Silver
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---
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# The Beautiful in the Ugly
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Functional programming is nice and all, but sometimes you just need to have
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things get done regardless of the consequences. Sometimes a dirty little hack
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will suffice in place of a branching construct. This is a story of one of these
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times.
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In shell script, bare words are interpreted as arbitrary commands for the shell
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to run, interpreted in its rules (simplified to make this story more interesting):
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1. The first word in a command is the name or path of the program being loaded
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2. Variable expansions are processed before commands are executed
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Given the following snippet of shell script:
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```shell
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#!/bin/sh
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# hello.sh
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function hello {
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echo "hello, $1"
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}
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$1 $2
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```
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When you run this without any arguments:
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```console
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$ sh ./hello.sh
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$
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```
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Nothing happens.
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Change it to the following:
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```console
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$ sh ./hello.sh hello world
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hello, world
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$ sh ./hello.sh ls
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hello.sh
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```
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Shell commands are bare words. Variable expansion can turn into execution.
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Normally, this is terrifying. This is useful in fringe cases.
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Consider the following script:
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```shell
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#!/bin/sh
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# build.sh <action> [arguments]
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projbase=github.com/Xe/printerfacts
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function gitrev {
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git rev-parse HEAD
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}
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function app {
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export GOBIN="$(pwd)"/bin
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go install github.com/Xe/printerfacts/cmd/printerfacts
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}
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function install_system {
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app
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cp ./bin/printerfacts /usr/local/bin/printerfacts
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}
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function docker {
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docker build -t xena/printerfacts .
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docker build -t xena/printerfacts:"$(gitrev)"
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}
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function deploy {
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docker tag xena/printerfacts:"$(gitrev)" registry.heroku.com/printerfacts/web
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docker push registry.heroku.com/printerfacts/web
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}
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$*
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```
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