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Shell redirection cheatsheet

• Examples
  • stdout to file
  • stderr to file
  • stdout to stderr
  • stderr to stdout
  • stdout and stderr to file
  • string to stdin
• Reference

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#!/bin/bash

cat /dev/urandom | tr -dc A-Za-z0-9- | head -c 512

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semver rules

How:

• The Node package manager (npm)
• Golang Modules

handles semver range definitions.

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Fetch current Git commit SHA-1

Method 1

From within Git repository:

$ cd /path/to/git/repo
$ git rev-parse HEAD
c8f882b484eeb71068539fd02f04c5c2eada1c02

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Bash string manipulation cheatsheet

Assignment
Assign value to variable if variable is not already set, value is returned. Combine with a : no-op to discard/ignore return value.	${variable="value"} : ${variable="value"}

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NPM package.json template

Based on the properties (and ordering) outlined in the NPM docs.

Reference

• https://docs.npmjs.com/cli/v10/configuring-npm/package-json
• https://docs.npmjs.com/creating-and-publishing-scoped-public-packages
• https://nodejs.org/docs/latest-v20.x/api/packages.html#nodejs-packagejson-field-definitions

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Rsync delete orphan files from target only - no copy

Calling rsync in the following way, using --existing, --ignore-existing and --delete allows the following:

• Files at target that do not exist at source will be deleted.
• Skipping all file copy operations from source to target.

$ rsync \
 --delete \

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Nginx upstream HTTP keepalive config example

As per Nginx documentation, the key directives of proxy_http_version and proxy_set_header need to be set as per below:

upstream backend {
	server 127.0.0.1:8080;
	keepalive 8;
}

server {

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Cancel Ubuntu Grub2 menu after failed boot/shutdown

Use the following values in /etc/default/grub:

GRUB_HIDDEN_TIMEOUT=2
GRUB_HIDDEN_TIMEOUT_QUIET=true
GRUB_TIMEOUT=0
GRUB_RECORDFAIL_TIMEOUT=2

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Escaping token replace values for sed

In this case replacement is passed in $1. Will replace TOKEN_NAME in given /path/to/my/templatefile.txt.

The magic is sed --regexp-extended 's/[\/&]/\\&/g' - ensures replace value is not tripped up in call to sed.

#!/bin/bash -e

tokenReplace=$1