Notes to Self

Alex Sokolsky's Notes on Computers and Programming



The rest is history.

zsh startup

.zshenv → [.zprofile if login] → [.zshrc if interactive] → [.zlogin if login] → [.zlogout sometimes]

.zshenv is always sourced. It contains exported variables that should be available to other programs, e.g. $PATH, $EDITOR, $PAGER.

.zprofile is the same as .zlogin except that it’s sourced before .zshrc while .zlogin is sourced after .zshrc. According to the zsh documentation:

.zprofile is meant as an alternative to .zlogin for ksh fans; the two are not intended to be used together, although this could certainly be done if desired.

.zshrc is for interactive shell configuration. You set options for the interactive shell there with the setopt and unsetopt commands. You can also:

You also set any variables that are only used in the interactive shell (e.g. $LS_COLORS).

.zlogin is sourced on the start of a login shell but after .zshrc if the shell is also interactive. This file is often used to start X. Some systems start X on boot, so this file is not always very useful.

.zshenv, .zprofile, .zshrc

See dot-files

zsh/bash tips

here document

cat << EOF > session.txt
Your user name is: $(whoami)
Your current working directory is: $PWD
Your Bash version is: $ZSH_VERSION

Compare command output with expectations

diff -u expected.txt <(some command)

bash script header

#!/usr/bin/env bash
# Exit on error. Append "|| true" if you expect an error.
set -o errexit
# Exit on error inside any functions or subshells.
set -o errtrace
# Do not allow use of undefined vars. Use ${VAR:-} to use an undefined VAR
set -o nounset
# Catch the error in case mysqldump fails (but gzip succeeds) in `mysqldump |gzip`
set -o pipefail
# Turn on traces, useful while debugging but commented out by default
set -o xtrace

# add your commands below...

my example use

Shell Variables

From Shell-Variables:

Variable Description
PPID The process ID of the shell’s parent process.
PWD The current working directory as set by the cd builtin.
RANDOM Each time this parameter is referenced, it expands to a random integer between 0 and 32767.

From Special-Parameters:

Parameter Description
$* Positional parameters, starting from one.
$@ Positional parameters, starting from one.
$# Number of positional parameters in decimal.
$? Exit status of the most recently executed foreground pipeline.
$$ Process ID of the shell. In a subshell, it expands to the process ID of the invoking shell, not the subshell.
$! Process ID of the job most recently placed into the background.
$0 Name of the shell or shell script.
$1..$9 The first 9 additional parameters the script was called with.

Parameter Expansion

echo "${var}"
echo "Substitute the value of var."

echo "${var:-word}"
echo "If var is null or unset, word is substituted for var. The value of var does not change."

echo "${var:=word}"
echo "If var is null or unset, var is set to the value of word."

echo "${var:?message}"
echo "If var is null or unset, message is printed to standard error. This checks that variables are set correctly."

echo "${var:+word}"
echo "If var is set, word is substituted for var. The value of var does not change."

More details.

May combine with colon built-in to assign a default value to a variable, e.g.:

# TMPDIR is defined on MacOS
: "${TMPDIR:=/tmp}"