Essential tutorial bits for developers

This document is a collection of tutorial bits that I gather over time from topics ranging from simple bash commands and git gems to creating self-signed certifcates. It helps to have a common place to store these gems which can be easily searched.

Git

• List branches that contain a given commit

# search within a local branch
$ git branch --contains <commit>
# search across local and remote branches
$ git branch -r --contains <commit>

• List all commits in the current branch that are not in the remote branch

git cherry -v

• For a given file, find what commits were added to master relative to the local branch

git log --oneline HEAD..master -- <file>

• Change the author

git commit --amend --author="<Author Name> <email@address.com>"

• Show git root directory

git rev-parse --show-toplevel

Bash

• Check if stdin, stdout or stderr is attached to a terminal

# File descriptors for stdin, stdout and stderr are 0, 1 and 2 respectively.
# The bash builtin `-t` takes one of the above file descriptors and returns
# true if the descriptor is attached to a terminal and false otherwise. The
# following checks if stdout is attached to a terminal.
$ [ -t 1 ] && echo "Yes" || echo "No"
Yes
$ ([ -t 1 ] && echo "Yes" || echo "No") | cat
No

• Check if a given function or alias exists

# Bash builtin `type` determines if a given identifier is a function or an
# alias. For example, let's define a function `bar` and an alias `baz`
$ function bar() {
> echo "i am a bar function"
> }
$ alias baz='bar'
# Now, let's use the `type` builtin to determine the type of `bar` and `baz`
$ type -t bar
function
$ type -t baz
alias

Certificate generation

• Generate a keystore using the Java keytool

keytool -genkey -alias server -keyalg RSA -keysize 2048 -keystore cloud.jks

• Generate a certificate request

keytool -certreq -alias server -file cloud.csr.txt -keystore cloud.jks

• Import one or all entries from another keystore

keytool -importkeystore -srckeystore cloud.jks -destkeystore cloud.pkcs -srcstoretype JKS  -deststoretype PKCS12

• Generate a PEM from a pkcs12 formatted file

openssl pkcs12 -in cloud.pkcs -out cloud.pem

• Reveal the private key from the PEM file

openssl rsa -in cloud.pem -out cloud.key

• Generate a certificate from the certificate request and private key

openssl x509 -req -days 365 -in cloud.csr.txt -signkey cloud.key -out cloud.crt

• Convert CRT to PEM format

openssl x509 -in cloud.crt -out cloud.pem -outform PEM