Bash patterns

Check these links:

• https://github.com/progrium/bashstyle
• https://www.shellcheck.net/
• https://kvz.io/blog/2013/11/21/bash-best-practices/
• http://www.kfirlavi.com/blog/2012/11/14/defensive-bash-programming/
• http://wiki.bash-hackers.org/scripting/obsolete
• https://google.github.io/styleguide/shell.xml
• https://github.com/SimonBaeumer/bash-tricks

Examples

#!/usr/bin/env bash

set -o errexit
set -o nounset
set -o pipefail

readonly DIR="$( cd "$( dirname "$0" )" && pwd )"
readonly RANDOM_ID=$(head -c 24 /dev/urandom | base64)  # 33 chars
[[ "$TRACE" ]] && set -o xtrace

main() {
  if [[ $# -gt 0 ]]; then
    "$@"
  else
    default_cmd
  fi
  echo "DONE!"
}

[[ "$0" == "$BASH_SOURCE" ]] && time main "$@"

clean_value() {
  local v=${1,,}  # lowercase
  v="${v//[!a-z0-9-]/-}"  # only a-z0-9-
  echo "${v:0:63}"  # 63 max chars
}

URI_NO_SLASH_AT_END=${URI%%/}

cat <(echo "123")
base64 <(echo "123")  # echo "123" | base64

cat <(base64 --decode << EOF
MTIzCg==
EOF
)

is_osx() {
    [[ $('uname') == 'Darwin' ]]
}

is_linux() {
    [[ $('uname') == 'Linux' ]]
}

adddate() {
  # adds data to output: e.g. somecommand | adddate
  while IFS= read -r line; do
    echo "$(date +"[%F %T]") $line"
  done
}

if ! hash something 2>/dev/null; then
    echo "'something' was not found"
fi

# list symlinks
find "$HOME" -maxdepth 2 -type l -exec ls -lah --color {} + 2>/dev/null | sed -e 's/.* \(.* -> .*\)/\1/'


# add line if not exists
grep -Fq 'source ~/.myterminalrc' ~/.bashrc || echo 'source ~/.myterminalrc' >> ~/.bashrc

# skip N lines
tail -n +2 /tmp/csv_file_with_header.csv


# heredocs
# https://stackoverflow.com/questions/1167746/how-to-assign-a-heredoc-value-to-a-variable-in-bash
# https://stackoverflow.com/questions/4937792/using-variables-inside-a-bash-heredoc
VAR=$(cat <<'EOF'
something'bla"
$(dont-execute-this)
foo"bar"'
EOF
)

VAR=$(cat <<EOF
something'bla"
$(do-execute-this)
foo"bar"''
EOF
)

# for each argument run command, in parallel
printf '%s\n' "$@" | xargs -I{} -P4 -t echo foo {} bar


# UTF-8 emojis at https://apps.timwhitlock.info/emoji/tables/unicode or https://unicode.org/emoji/charts/full-emoji-list.html
RED='\033[0;31m'
GREEN='\033[0;32m'
NC='\033[0m' # No Color

cleanup_exit() {
  rv=$?
  # do some handling
  if [[ $rv != 0 ]]; then
    # echo with colors and emojis to stderr
    >&2 echo -e "\\U1F6A8\\U1F6A8\\U1F6A8\\U1F6A8\\U1F6A8 \\U274C${RED} Failed! \\U1F446 ${NC}\\U1F6A8\\U1F6A8\\U1F6A8\\U1F6A8\\U1F6A8"
    exit $rv
  else
    >&2 echo -e "\\U2705${GREEN} Completed successfully!${NC}"
  fi
}

trap "cleanup_exit" SIGQUIT SIGTERM EXIT

# create base dir if not exists
mkdir -p "$(dirname "$someFilePath")"

# check if variable is defined and non empty
[[ -n "${POSIBLY_EMPTY_VARIABLE:-}" ]]