====== Shell Programmierung (bash) ======

==== Abarbeitung der Kommandozeile ====
| Read until the first command separator | & && \| \| ; < > |
| Split the command | cat /etc/passwd \| wc -l |
| substitute variables | $MYVAR wird durch Wert ersetzt |
| substitute commands | Backticks oder () |
| stdin, stdout and stderr| re(>/dev/null, 2>&1,...)|
| Zuweisungen an Variablen durchführen| |
| Sonderzeichen ersetzen| Sonderzeichen wie *, ?, [] werden ersetzt. Ausser Sie stehen in "" |
| Fertiges Kommando ausführen |  |

==== AWK ====

|FS|Separator|
|RS|Record Sepatator. Normally Linbreak (\n)|
|NF|Number of Fields in a Record|
|NR|Number of active Record|
|ARGV|Array of all awk parameters|
|ARGC|number of all awk parameters|
|OFS|Output field separator|
|ORS|Output record separator|


   awk '{print $0}'
   df -hk | egrep "\/$" | awk '{print $5}'
   df -hk | awk '/sda/{print $5}'
   df -hk | awk 'NR>1{print $1,$3,$7}'

==== Commandos ====
|exec||
|break||
|continue||
|declare||
|eval||
|getops||
|let||
|login|| 
|umask||
|readonly||
|trap||
|type||
|typset||
|exit||

==== Funktionen ====

  summe()
  {
    MYVAR1=$1
    MYVAR2=$2
    "let ERG=$MYVAR1+$MYVAR2"
    ECHO $ERG
  }
  ERG=`summe 5 6` 
  echo $ERG




==== Variablen ====

  HISTSIZE 
  TMOUT
  ENV
  OSTYPE
  HOSTTYPE

==== Umleiten ====

  STDIN < 
  STDOUT > >> 
  STDERR 2> 

Example: bypass STDERR to STDOUT
  2>&1

Example: bypass STDOUT and STDERR
  >/dev/null 2>&1

==== IF ====

Comparison:
  if [ $VAR == "string" ]
     machwas
  fi
  if [ $VAR -eq 5 ]
     machwas
  fi
Weitere Parameter: -lt, -gt, !=, <, >

==== Meta-Zeichen ====

  ?(string) 0-1mal string
  *(string) x-mal string
  +(string) 1-xmal string
  @(string) 1mal string
  !(string) nicht string

==== TEST-Command ====

Check Files or Directories 

  test -d directory
  test -e file
  test -f file
  test ! ( ausdruck)




==== WHILE ====

   while [ expression ]
   do
       dosomething
   done
   
==== WHILE lines in file ====

   while read i; do
      echo $i
   done < list.txt