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Shell

OS​

Unix​

  • Bash
  • Zsh

Windows​

Mac OS X​

  • Bash

Tools​

  • shellcheck
  • makeself

Invocation​

Restricted Shell​

Login Shell​

echo $0
-bash
  • /etc/profile
  • ~/.bash_profile
  • ~/.bash_login
  • ~/.profile
  • ~/.bash_logout

Non-Login Shell​

echo $0
bash
  • /etc/bash.bashrc
  • ~/.bashrc

Interactive Shell​

Non-Interactive Shell​

SH​

POSIX​

Bash Options​

set(POSIX)​

  • set -o vi/set -o emacs

shopt​

SubShell​

SubShellNon-SubShell
(){}
|

Reserved Words​

  • function/{}
  • if/then/elif/else/fi
  • while/until/for/in/do/done
  • case/esac
  • select
  • [[]]/!
  • coproc
  • time

Control Operator​

  • ||
  • &&
  • &
  • ;
  • ;;
  • ;&
  • ;;&
  • |
  • |&(2>&1)
  • (
  • )

Quoting​

  • Escape Character
    • \(backslash)
  • Single Quotes
  • Double Quotes
  • ANSI-C Quoting(man echo)

Comment​

CommentDescription
#one-line comment
:' \n This is a \n multi line comment \n 'multiple lines comment

Internal Variables​

VariableComment
$N($0,$1,$2)Positional parameters, passed from command line to script, passed to a function, or set to a variable
$#Number of command-line arguments or positional parameters
#*All of the positional parameters, seen as a single word
$@Same as $*, but each parameter is a quoted string, that is, the parameters are passed on intact, without interpretation or expansion. This means, among other things, that each parameter in the argument list is seen as a separate word
$?Exit status of a command, function, or the script itself
$!PID (process ID) of last job run in background
$$PID of shell
$_Special variable set to final argument of previous command executed

Constructs​

Sequence​

Loop​

# Keywors: until while for break continue

# Basic for loop
for i in /etc/rc.*; do
  echo $i
done

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

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

for i in {5..50..5}; do
    echo "Welcome $i"
done

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

# Forever
while true; do
  ···
done

Conditionals​

# Test
[[ -z STRING ]] # Empty string
[[ -n STRING ]] # Not empty string
[[ STRING == STRING ]] # Equal
[[ STRING != STRING ]] # Not Equal
[[ NUM -eq NUM ]]       # Equal
[[ NUM -ne NUM ]]       # Not equal
[[ NUM -lt NUM ]]       # Less than
[[ NUM -le NUM ]]       # Less than or equal
[[ NUM -gt NUM ]]       # Greater than
[[ NUM -ge NUM ]]       # Greater than or equal
[[ STRING =~ STRING ]]  # Regexp
(( NUM < NUM )) # Numeric conditions
# File
[[ -e FILE ]] # Exists
[[ -r FILE ]] # Readable
[[ -h FILE ]] # Symlink
[[ -d FILE ]] # Directory
[[ -w FILE ]] # Writable
[[ -s FILE ]] # Size is > 0 bytes
[[ -f FILE ]] # File
[[ -x FILE ]] # Executable
[[ FILE1 -nt FILE2 ]] # 1 is more recent than 2
[[ FILE1 -ot FILE2 ]] # 2 is more recent than 1
[[ FILE1 -ef FILE2 ]] # Same files
# More conditions
[[ -o noclobber ]]      # If OPTIONNAME is enabled
[[ ! EXPR ]]    # Not
[[ X && Y ]]    # And
[[ X || Y ]]    # Or

# Keywors: if case select
if [[ -z "$string" ]]; then
  echo "String is empty"
elif [[ -n "$string" ]]; then
  echo "String is not empty"
fi

# case
case "$1" in
  start | up)
    vagrant up
    ;;

  *)
    echo "Usage: $0 {start|stop|ssh}"
    ;;
esac

Return/Exit​

  • return
  • exit

Expansion​

  • Brace

    {A,B}.js
    {1..5}

  • Parameter

    name="John"
    echo ${name}
    echo ${name/J/j}    #=> "john" (substitution)
    echo ${name:0:2}    #=> "Jo" (slicing)
    echo ${name::2}     #=> "Jo" (slicing)
    echo ${name::-1}    #=> "Joh" (slicing)
    echo ${name:(-1)}   #=> "n" (slicing from right)
    echo ${name:(-2):1} #=> "h" (slicing from right)
    echo ${food:-Cake}  #=> $food or "Cake"

Data Type​

String​

Number​

Arrays​

Fruits=('Apple' 'Banana' 'Orange')
Fruits[0]="Apple"
Fruits[1]="Banana"
Fruits[2]="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 "${arrayName[@]}"; do
  echo $i
done

Dictionary​

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

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

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

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

IO​

Input​

Here Document​

cat << EOF
#!/usr/bin/env bash
true
EOF

Here String​

# <<< = |

read FIRST SECOND <<< "Hello World"
echo "Hello World" | read FIRST SECOND # read run in subshell

Output​

Process​

  • Parallel
  • xargs

History​

CommandDescription
!!Execute last command again
!$Expand last parameter of most recent command
!*Expand all parameters of most recent command
!Expand most recent invocation of command

Projects​

Mindmaps​

Reference​