## Arrays
```bash
distro=("redhat" "debian" "gentoo")
echo ${distro[0]}
echo ${distro[2]}  # will print gentoo
echo ${#distro[@]} # print array size, here 3

tLen=${#distro[@]}
for (( i=0; i<${tLen}; i++ ));
do
  echo ${distro[$i]}
done
```

## Basic
```bash
foo="asdf"
echo${#foo} # 4 - lenght of foo
```
### Incrementation
```bash
i=0
((i++)) # i=1
((i+=3)) # i=4
```
### Command substitution
```bash
$(cmd) # POSIX
`cmd` # more or less obsolete for Bash
$((cmd)) # arithmetic expansion
$( (cmd) ) # explicit subshell (cmd) inside the command substitution $( )
```
#### Nesting
```bash
echo `echo `ls``      # INCORRECT
echo `echo \`ls\``    # CORRECT
echo $(echo $(ls))    # CORRECT
echo "$(echo "$(ls)")" # nested double-quotes
```
### Condition execution
```bash
git commit && git push
git commit || echo "Commit failed"
```

## Parameter expansions
### Substitution
```bash
STR="/path/to/foo.cpp"
# ${FOO%suffix}	Remove first suffix
echo ${STR%.cpp}    # /path/to/foo
echo ${STR%.cpp}.o  # /path/to/foo.o
# ${FOO%%suffix}	Remove long suffix

# ${FOO#prefix}	Remove prefix
echo ${STR#*/}      # path/to/foo.cpp
# ${FOO##prefix}	Remove long prefix
echo ${STR##*.}     # cpp (extension)
echo ${STR##*/}     # foo.cpp (basepath)
# ${FOO/from/to}	Replace first match
echo ${STR/foo/bar} # /path/to/bar.cpp
name="Johnny"
echo ${name/n/N}    #=> "JohNny"
# ${FOO//from/to}	Replace all
echo ${name/n/N}    #=> "JohNNy"
# ${FOO/%from/to}	Replace suffix
BASE=${STR##*/}   #=> "foo.cpp" (basepath)
DIR=${SRC%$BASE}  #=> "/path/to" (dirpath)
# ${FOO/#from/to}	Replace prefix

```
### Substrings
```bash
name="Johnny"
# ${FOO:0:2}	Substring (position, length)
echo ${name:0:2}    #=> "Jo"
echo ${name:0:-2}   #=> "John"
```
### Default values
```bash
# ${FOO:-val}	return $FOO, or val if $FOO not set
unset foo
echo ${food:-Cake}  #=> "Cake"
echo $food          #=> ""
food="Pie"
echo ${food:-Cake}  #=> "Pie"
# ${FOO:=val}	Set $FOO to val if $FOO not set
unset foo
echo ${food:=Cake}  #=> "Cake"
echo $food          #=> "Cake"
food="Pie"
echo ${food:=Cake}  #=> "Pie"
# ${FOO:+val}	return val if $FOO is set
unset foo
echo ${food:+Cake}  #=> ""
echo $food          #=> ""
food="Pie"
echo ${food:+Cake}  #=> "Cake"
# ${FOO:?message}	Show error message and exit if $FOO is not set