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
"

Cool code sample of a function call using args and the use of the return code

#!/bin/bash
main() {
 declare test_path='/etc'
 declare test_file='motd'
 chkFile "${test_path}/${test_file}"	
 myreturnvalue=$?
 #echo "myreturnvalue is "$myreturnvalue
 if [ $myreturnvalue == "1" ] ; then   #Check for Debian
  echo "File exist: ${test_path}/${test_file}"
 else
  echo "File does NOT exist: ${test_path}/${test_file}"
 fi
 }
 function chkFile(){
  if [ -f $1  ]; then   #Check for file
   return 1
  else 
   return 0
  fi
 }
main "$@"; exit 0