Simple and quick bash scripting reference

simple-cheatsheet.sh

#!/bin/bash
#----------
# simple-cheatsheet.sh
#
# source: https://devhints.io/bash
#
#----------

# Variables
NAME="John"
echo $NAME
echo "$NAME"
echo "${NAME}!"

# Conditional execution
git commit && git push
git commit || echo "Commit failed"

## Creating directory if it doesn't exist
dest_dir="/tmp/test"
[[ ! -d $dest_dir ]] && mkdir $dest_dir

# Arrays
fruits=('Apple' 'Banana' 'Orange')

echo ${fruits[0]}           # Element #0
echo ${fruits[-1]}          # Last element
echo ${fruits[@]}           # All elements, space-separated
echo ${#fruits[@]}          # Number of elements
echo ${#fruits}             # String length of the 1st element
echo ${#fruits[3]}          # String length of the Nth element
echo ${fruits[@]:3:2}       # Range (from position 3, length 2)
echo ${!fruits[@]}          # Keys of all elements, space-separated

for i in "${fruits[@]}"; do
  echo $i
done

fruits=("${fruits[@]}" "Watermelon")    # Push
fruits+=('Watermelon')                  # Also Push
fruits=( ${fruits[@]/Ap*/} )            # Remove by regex match
unset fruits[2]                         # Remove one item
fruits=("${fruits[@]}")                 # Duplicate
fruits=("${fruits[@]}" "${Veggies[@]}") # Concatenate
lines=(`cat "logfile"`)                 # Read from file

# Dictionaries
declare -A sounds

sounds[dog]="bark"
sounds[cow]="moo"
sounds[bird]="tweet"
sounds[wolf]="howl"

for val in "${sounds[@]}"; do
  echo $val
done

for key in "${!sounds[@]}"; do
  echo $key
done

echo ${sounds[dog]}     # Dog's sound
echo ${sounds[@]}       # All values
echo ${!sounds[@]}      # All keys
echo ${#sounds[@]}      # Number of elements
unset sounds[dog]       # Delete dog

# Heredoc

cat <<END >production.txt
[my box]
0.0.0.0
END

# Conditionals

## String
if [[ -z "$string" ]]; then
  echo "String is empty"
elif [[ -n "$string" ]]; then
  echo "String is not empty"
else
  echo "This never happens"
fi

## Equal
a="foo"
b="foo"
if [[ "$a" == "$b" ]]; then
  echo "equal"
fi

## Regex
a="testing"
if [[ "$a" =~ ^test$ ]]; then
  echo "match"
fi

## replacing all
foo="foobarfoobarfoo"
echo ${foo//foo/bar}

## smaller
if (( $a < $b )); then
   echo "$a is smaller than $b"
fi

## checking file
if [[ -e "file.txt" ]]; then
  echo "file exists"
fi

# Functions
myfunc() {
    echo "hello $1"
}

myfunc "Lucas"

#-- returning values
myfunc() {
    local myresult='some value'
    echo $myresult
}
result="$(myfunc)"

# Ranges
for i in {1..5}; do
    echo "Welcome $i"
done

# C-like loop
for ((i = 0 ; i < 100 ; i++)); do
  echo $i
done

# Basic loop
for i in /tmp/*; do
  echo $i
done

# Reading files line by line
cat file.txt | while read line; do
  echo $line
done