bash-cheatsheet.md

Bash cheatsheet

Google Shell Style Guide

Output

echo "Hello World"
printf "Hello World\n"

Format string for printf

• %s String
• %d Decimal
• %f Float
• %x Hexadecimal
• \n New line
• \t Tab

Positional parameters

• $# Number of parameters
• $0 Script name
• $1 First parameter
• $2 Second parameter

Reading a file

while IFS="" read LINE do
  echo "$LINE"
done < "file.txt"

Assigning shell ouput

cmdoutput=$(ls -l)

If statements

if cond then
  cmd_a
else
  cmd_b
fi

File and numerical conditions

if [[ -e $filename ]] then
  echo "$filename exists"
fi

File test

• -d Directory exists
• -e File exists
• -r File is readable
• -w File is writable
• -x File is executable

Numeric test

• -eq Equal
• -gt Greater than
• -lt Less than

a=3
b=1
if [ "$a" -gt "$b" ]; then
  echo "$a is greater"
fi

while loops

i=0
while (( i < 1000 )) do
  let i++
done

for loops

for ((i=0; i < 10; i++)) do
  echo "$i"
done

for item in alice bob tom; do
  echo "$item"
done

for i in $(seq 1 10); do echo $i; done

case statement

case $var in
  "bob")
    echo "Bye Bob!"
    ;;
  "alice")
    echo "Bye Alice!"
    ;;
  "tom")
    echo "Bye Tom!"
    ;;
  *)
    echo "Bye!"
    exit
    ;;
esac

Functions

function hello_friend () {
  name=$1
  echo "Hello $name"
}  

hello_friend "Alice"

Arrays

declare -a files=(
  "/usr/local/etc/php-fpm.d/php-fpm-pool.conf"
  "/etc/nginx/conf.d/test.conf"
  "/usr/local/etc/php/php.ini"
)

for file in "${files[@]}"; do
  echo $file
done

Hashmaps

declare -A hash=(
  [HDD]=Brand1
  [Monitor]=Brand2
  [Keyboard]=Brand3
)

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

Search and replace

name="NumberThreeNumberThree"

# All occurrences
filename="${name//Three/3}"

# First occurrence
filename="${name/Three/3}"

echo "$filename"

Heredoc

# Creating a .gitlab-ci.yml in current directory
cat <<EOF > .gitlab-ci.yml
image: busybox:latest
include:
  - template: Security/Secret-Detection.gitlab-ci.yml
test:
  stage: test
  script:
    - /bin/sh -c 'echo "Do nothing"'
EOF