Bash cheat sheet

• Getoptions with flags

while getopts "f" option; do   
 case ${option} in
 f)
     flag="1"
 *)
     echo "unknown parameter"
     exit;;
  esac
done

• Getoptions with args

while getopts "a:" option; do   
 case ${option} in
 a)
     arg="${OPTARG}"
 *)
     echo "unknown parameter"
     exit;;
  esac
done

• Condition -OR-

if "$isA" || "$isB"; then
 do-something
fi 

• Condition if var is defined

if [ ${var+x} ]; then 
 do-something
fi

• Print Text

cat << EOF
Any ...
text ... 
EOF
}

• Read tokenized configuration file

. /etc/os-release
echo $VERSION_ID

• Search in file, return bool

if grep -q search-arg "/etc/file.conf"; then
 do-something
fi

• Search and replace

sed -i -r  's/(.*)umask 022(.*)$/\t#Changed\n\tumask 027/gi' /etc/profile

• CRLF within string

scriptmsg+="Hello\n"
scriptmsg+="World\n"
echo -e $scriptmsg

NL=$'\n'
echo -e " Hello${NL}Wolrd"

echo "
Hello
World
"