code_conventions.md

echo x${output}x

Trim leading whitespaces

output="${output##*( )}"

echo x${output}x

trim trailing whitespaces

output="${output%%*( )}"

echo x${output}x

Find file extension

ext="${file##*.}" # string after last '.'

Put these lines at the top and bootom of your bashrc

PS4='+ $(date "+%s.%N")\011 ' exec 3>&2 2>$HOME/bashstart.$$.log set -x

code

set +x exec 2>&3 3>&-

Mac OS X: Darwin refers to the underlying kernel and terminal utilities put together by Apple, which has slightly different (BSD?) implementations than Arch Linux (GNU?). Shell scripts are called OSX when they refer more to the OS X userspace.

Arch Linux: Upgrade fails. Usually because it's been a while since last upgrade.

Try upgrading important packages by themselves: arch-linux-keyring pgp linux

Perhaps write a scriptc that searches for "base" upgrades, and runs that first, then runs upgrade again.

Keep a directory empty in git (and ignore new files)

echo '# Ignore everything in this directory *

Except this file

!.gitignore ' >> EMPTY_DIRECTORY/.gitignore

Keep an empty directory in git (but allow files later)

touch EMPTY_DIRECTORY/.gitignore

Aliases are passe. Use functions instead!

#alias cd 'cd !*; ls' # This is how to include args in an alias

A function:

buzz() { echo "buzz" }

Escape UTF-8 characters into their 3-byte format

escape() { printf "\\x%s" $(printf "$@" | xxd -p -c1 -u) }

Create a data URL from a file

data_url() { local mimeType=$(file -b --mime-type "$1") if test $mimeType = text/*; then mimeType="${mimeType};charset=utf-8" fi echo "data:${mimeType};base64,$(openssl base64 -in "$1" | tr -d '\n')" }

Scripts should be 'sourced' into the shell, because they use shell language. trying to run a script as an executable is just a layer of obfuscation in a subprocess.

Dotfiles should stay as terminal settings, not full-blown portable programs.

The difference between a shell function and a script is that a shell function is an atomic action typed by hand and returned to the terminal immediately. A script takes more time or is usually executed as/by another process. A shell function should be merely a modified way to start another program. A script is defined by the programming logic it is written in, and is a program in itself.

IFS="$(printf '\n\t')"

WARNING: Setting environment variables from URI this way is insecure!

IFS="&" #set -- $QUERY_STRING #array=($@) #array=($QUERY_STRING) #for var in "${array[@]}"; do for var in $QUERY_STRING; do #IFS="=" #set -- "$var" #declare "$1=$2" declare "$var" done

URL Decode: Replace %NN with \xNN and pass the lot to printf -b, which will decode hex

test -z "$location" && location=/ || printf -v location '%b' "${location//%/\x}"

A shell's functions are to assist in executing files, managing files, managing processes, and serving files+pipes to processes, to aid in browsing/displaying/editing.

It excells at doing this locally and remotely because it is a text interface, but smart command+file completion, suggestion, and highlighting is paramount.

Currently I use '&>/dev/null' and '>file' without a space in the name. The shortcuts '&2' and '&1' are not very clear, but are sometimes unavoidable.

Only export variables that might be used by other programs. Do not export variables specific to the functionality of the shell

Shell script naming priority should try to be as specific as possible (shell name whenever possible). Scripts are sourced in this order:

Does it work only in your SHELL? or is it important for any tty or shell (SH)? Does it work only on your distro (ID)? or is it important for any of the same kernel (OS)? SHELL (program) > SH (any shell) > ID (distro) > OS (kernel) example: .bash > .sh > .arch > .linux

if connected; then true fi

test ! connected && echo "Error: No internet connectivity." >/dev/stderr && return 1

This automatically passes the last command's return value

test $EUID = 0 || return

This allows you to print an error and then return a nonzero value

test $EUID != 0 && echo "Error: You must be root to do this." >/dev/stderr && return 1

Always use '&&' and '||' together in that order!

(if) true && (then) || (if) false && || (else)

Put another way:

true && || false && ||

Remember that this only works if the second term CAN NOT FAIL

This would be very bad, because all three commands are run:

true: && false: ||

unset ANSWER echo -n "Do this thing? [y/N] " read ANSWER ANSWER=$(echo "$ANSWER" | tr '[:upper:]' '[:lower:]') if test "$ANSWER" = "y" || test "$ANSWER" = "yes"; then true fi

unset ANSWER echo -n "Do you agree with this? [yes or no]: " read ANSWER case $ANSWER in [yY] | [yY][Ee][Ss] ) true ;;

[nN] | [n|N][O|o] ) false ;; *) echo "Error: Invalid input" >/dev/stderr esac

Secure temporary files

tmp=${TMPDIR:-/tmp} tmp=${tmp}/tempdir.$$ $(umask 077 && mkdir $tmp) || echo "Error: Could not create temporary directory." >/dev/stderr && return 1 Basic shell mistakes: relying on quoting errors to relay arguments (instead of using arrays), convoluted grep+sed pipes (instead of awk), echo -e (instead of printf), ancient backtick format (instead of $())