Bash scripting cheatsheet

Esempio

#!/usr/bin/env bash NAME="John" echo "Hello $NAME!"

Variabili

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

Quotes delle stringhe

NAME="John" echo "Hi $NAME"  #=> Hi John echo 'Hi $NAME'  #=> Hi $NAME

Esecuzione di comandi

echo "I'm in $(pwd)" echo "I'm in `pwd`" # Same

Esecuzione condizionale

git commit && git push git commit || echo "Commit failed"

Funzioni

get_name() {   echo "John" } echo "You are $(get_name)"

If.. Then.. Else...

if [[ -z "$string" ]]; then   echo "String is empty" elif [[ -n "$string" ]]; then   echo "String is not empty" fi

Strict mode

set -euo pipefail IFS=$'\n\t'

Espansione di stringhe

echo {A,B}.js

Manipolazione di stringhe

Basics

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" length=2
echo ${name:0:length}
#=> "Jo"

STR="/path/to/foo.cpp"
echo ${STR%.cpp}
# /path/to/foo
echo ${STR%.cpp}.o  
# /path/to/foo.o
echo ${STR##*.}     
# cpp (extension)
echo ${STR##*/}
# foo.cpp (basepath)
echo ${STR#*/}
# path/to/foo.cpp
echo ${STR##*/}
# foo.cpp echo
${STR/foo/bar}
# /path/to/bar.cpp
STR="Hello world"
echo ${STR:6:5}
# "world"
echo ${STR:-5:5}
# "world"
SRC="/path/to/foo.cpp"
BASE=${SRC##*/}
#=> "foo.cpp" (basepath)
DIR=${SRC%$BASE}
#=> "/path/to/" (dirpath)

Sostituzione

Sottostringhe

Lunghezza

Valori di default

The : is optional (eg, ${FOO=word} works)

Cicli

For

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

For (C-like)

for ((i = 0 ; i < 100 ; i++)); do
echo $i
done

For (Intervallo)

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

For (Intervallo e passo)

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

Lettura di righe da file

< file.txt | while read line; do
echo
$line
done

Ciclo infinito

while true; do
···
done

Funzioni

Definizione di funzioni

myfunc() {
echo "hello $1"
} 
# Same as above (alternate syntax) 
function myfunc() {
echo "hello $1"
} 
myfunc "John"

Valori di ritorno

myfunc() {
local myresult='some value'
echo $myresult
}
result="$(myfunc)"

Gestione errori

myfunc() {
return 1
} 

if myfunc; then
echo "success"
else
echo "failure"
fi

Argomenti delle funzioni

Espressioni condizionali

Conditioni

NB [[ è un comando a tutti gli effetti che restituisce 0 (true) o 1 (false). Qualunque programma che utilizza la stessa logica (come tutti quelli base come grep(1) o ping(1)) possono essere usati come condizioni.

Condizioni sui file

Example

if ping -c 1 google.com; then   echo "It appears you have a working internet connection" fi if grep -q 'foo' ~/.bash_history; then   echo "You appear to have typed 'foo' in the past" fi # String if [[ -z "$string" ]]; then   echo "String is empty" elif [[ -n "$string" ]]; then   echo "String is not empty" fi # Combinations if [[ X ]] && [[ Y ]]; then   ... fi # Equal if [[ "$A" == "$B" ]] # Regex if [[ "A" =~ "." ]] if (( $a < $b )); then    echo "$a is smaller than $b" fi if [[ -e "file.txt" ]]; then   echo "file exists" fi

Arrays

Defining arrays

Fruits=('Apple' 'Banana' 'Orange') Fruits[0]="Apple" Fruits[1]="Banana" Fruits[2]="Orange"

Working with arrays

echo ${Fruits[0]}           # Element #0 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)

Operations

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

Iteration

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

Dictionaries

Defining

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

Declares sound as a Dictionary object (aka associative array).

Working with dictionaries

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

Iteration

Iterate over values

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

Iterate over keys

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

Options

Options

set -o noclobber  # Avoid overlay files (echo "hi" > foo) set -o errexit    # Used to exit upon error, avoiding cascading errors set -o pipefail   # Unveils hidden failures set -o nounset    # Exposes unset variables

Glob options

set -o nullglob    # Non-matching globs are removed  ('*.foo' => '') set -o failglob    # Non-matching globs throw errors set -o nocaseglob  # Case insensitive globs set -o globdots    # Wildcards match dotfiles ("*.sh" => ".foo.sh") set -o globstar    # Allow ** for recursive matches ('lib/**/*.rb' => 'lib/a/b/c.rb')

Set GLOBIGNORE as a colon-separated list of patterns to be removed from glob matches.

History

Commands

Expansions

Operations

!! and !$ can be replaced with any valid expansion.

Slices

!! can be replaced with any valid expansion i.e. !cat, !-2, !42, etc.

Miscellaneous

Numeric calculations

$((a + 200))      # Add 200 to $a $((RANDOM%=200))  # Random number 0..200

Subshells

(cd somedir; echo "I'm now in $PWD") pwd # still in first directory

Redirection

python hello.py > output.txt   # stdout to (file) python hello.py >> output.txt  # stdout to (file), append python hello.py 2> error.log   # stderr to (file) python hello.py 2>&1           # stderr to stdout python hello.py 2>/dev/null    # stderr to (null) python hello.py &>/dev/null    # stdout and stderr to (null) python hello.py < foo.txt      # feed foo.txt to stdin for python

Inspecting commands

command -V cd #=> "cd is a function/alias/whatever"

Trap errors

trap 'echo Error at about $LINENO' ERR

or

traperr() {   echo "ERROR: ${BASH_SOURCE[1]} at about ${BASH_LINENO[0]}" } set -o errtrace trap traperr ERR

Case/switch

case "$1" in   start | up)     vagrant up     ;;   *)     echo "Usage: $0 {start|stop|ssh}"     ;; esac

Source relative

source "${0%/*}/../share/foo.sh"

printf

printf "Hello %s, I'm %s" Sven Olga #=> "Hello Sven, I'm Olga

Directory of script

DIR="${0%/*}"

Getting options

while [[ "$1" =~ ^- && ! "$1" == "--" ]]; do case $1 in   -V | --version )     echo $version     exit     ;;   -s | --string )     shift; string=$1     ;;   -f | --flag )     flag=1     ;; esac; shift; done if [[ "$1" == '--' ]]; then shift; fi

Heredoc

cat <<END hello world END

Reading input

echo -n "Proceed? [y/n]: " read ans echo $ans read -n 1 ans    # Just one character