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Bash

1. Ctrl + A Go to the beginning of the line you are currently typing on
2. Ctrl + E Go to the end of the line you are currently typing on
3. Ctrl + L Clears the Screen, similar to the clear command
4. Ctrl + U Clears the line before the cursor position. If you are at the end of the line, clears the entire line.
5. Ctrl + H Same as backspace
6. Ctrl + R Let's you search through previously used commands
7. Ctrl + C Kill whatever you are running
8. Ctrl + D Exit the current shell
9. Ctrl + Z Puts whatever you are running into a suspended background process. fg restores it.
10. Ctrl + W Delete the word before the cursor
11. Ctrl + K Clear the line after the cursor
12. Ctrl + T Swap the last two characters before the cursor
13. Esc + T Swap the last two words before the cursor
14. Alt + F Move cursor forward one word on the current line
15. Alt + B Move cursor backward one word on the current line
16. Tab Auto-complete files and folder names

Liste wichtiger Dateien, Verzeichnisse und Anwendungen:

• Interne BASH-Funktionen und -Befehle
• ~/.bash_profile
• ~/.bash_login
• ~/.profile
• ~/.bashrc
• ~/.bash_logout
• ~/.inputrc
• function
• export
• env
• set
• lists
• seq
• unset

 variable=value
 a="aasdf"
 echo $a
 echo 

We have shell and enviroment variables. With the command "export" you can declare a already defined shell variable to an enviroment variable. The command "env" returns all the exported variables. With "set" you get exported variables and the shell variables. With "export -n variable" you can annihilate the earlier export or makes an enviroment variable to a shell variable. With "unset" you can kill the variable.

The difference between login shells and shells which only execute a script is the start up process. The login shell processes first the "/etc/profile" file, then "~/.bash_profile" or "~/.bash_login" or "~/.profile" dependent which one was first founded. A normal shell first executes "/etc/bash.bashrc" and "~/.bashrc" if it exists. At the end of a shell it will be executed the file "~/.bash_logout"

history

 history -c

 history -w file

1.109.2 Anpassen oder Schreiben einfacher Scripts (weight: 3)

Beschreibung: Die Kandidaten sollen in der Lage sein, existierende Scripts anzupassen oder einfache neue BASH-Scripts zu schreiben.

Wichtigste Wissensgebiete:

• Standard-Syntax der sh gebrauchen (Schleifen, Tests).
• Befehlssubstitution benutzen.
• Auswertung der Rückgabewerte (Erfolg, Fehler) oder anderen Informationen eines aufgerufenen Befehls.
• Bedingter E-Mail-Versand an den Administrator.
• Richtige Wahl des Script-Interpreters durch die Shebang-Zeile (#!).
• Verwalten von Speicherort, Besitz- und Ausführungs- und suid-Rechte von Scripten.

Liste wichtiger Dateien, Verzeichnisse und Anwendungen:

• for
• while
• test
• chmod

Under linux it is not possible to get root rights with the use of the sticky bit. You can set the bit but it will be futile.

if ... then ... elif ... else ... fi

 if test -f /etc/fstab;
 then
   echo "asdf";
 else
   echo "kkkkk";
 fi

Equivalent to "test -a /etc/fstab" is "[ -a /etc/fstab ]".

Test options: Keep in mind the spaces between stings!!! Unless the command test return always true.

 -d file

 -f file

 -r file 

 -w file

 -x

 -z string

 -n string 

 str = str2
 str != str2
 str -lt str2
 str -gt str2

for and while loops

 $for i in 1 2 3;do echo $i;done
 $while true;do echo "I was here";done
 $ for i in $(seq 1 1000);do echo $i;done

backticks and brackets

The backtick method is the older one. To replace a string with its result use `...`:

 now=`date +%F`

The newer method is

 now=$(date +%F)

and has the advantage that you can use nested forms.

With "seq" you can give a sequence of numbers:

 for i in $(seq 1 1000);do echo $i;done

What is happening when we execute the following script?

 #!/bin/bash
 cd ..

Response: nothing, because the shell will execute the script with a new shell, then it goes up a directory and ends its execution. Therefore it lands again at the start directory. Such a functionality can only be made by a shell function:

 up() { cd ..; }

Attend the space between "{" and the first command. It is not for well form related but syntactical.

With $1, $2 and so on you can touch the arguments to the script. $0 is the name of the script and $@ the whole set of arguments.

With $$ you can access the process id of the script.

 $ echo My id is $$
 My id is 5027

 $? is the errorcode of the last process.

Very useful is also the variable $! which is assigned with the value of the process id of the last started background process.

 $ find / -name "*.txt" -print &
 $ kill $!

 $* all arguments in one string
 $@ all arguments in an array of strings
 $# number of arguments in the command line
 $_ last argument of the process which was called at last

Automatic variables:

 $RANDOM  radom number between 0 and 32767
 $LINENO
 $OLDPWD
 $OPTARG
 $PPID
 $PWD
 $REPLY   is set by command read if no variable is given
 $SECONDS number of seconds since last start or login of the current shell

Getting the options from command line

getopts delivers the options and even wrong parameters.

 while getopts abc:D: opt
 do
   case $opt in
     a) echo "Option a wurde angegeben";;
     b) echo "Option b wurde angegeben";;
     c) echo "Option c wurde angegeben: $OPTARG";;
     D) echo "Option D wurde angegeben: $OPTARG";;
    esac
 done

parameters beyond $9

 echo "the 20th argument: ${20}"

comparison of numbers

 [ "$var1" = "$var2" ]
 [ "$var1" != "$var2" ]
 [ -z "$var2" ]     # var empty?
 [ -n "$var3" ]     # var not empty?

printf

 printf format arg1 arg2 ...
 %c char
 %s string
 i integer
 %u integer
 %f real
 E real exponetial 
 X integer hex
  escape char for %

Example

 $cat results.txt
 Michael Foerster;45;20;17;20;17;-;-;74
 Frank Sebastian Haensch;2;17;20;15;20;-;-;72

 for data in $(cat results.txt)
 do
   name=$(echo $data | cut -d\; -f1 )
   nr=$(echo $data | cut -d\; -f2)
   punkte=$(echo $data | cut -d\; -f9)
   printf "Fahrer %30s     Nr %3d Punkte %4d\n" $name $nr $punkte
 done

 Fahrer               Michael_Foerster     Nr  45 Punkte   74
 Fahrer        Frank_Sebastian_Haensch     Nr   2 Punkte   72

adjust console view with tput

 $ echo "`tput bold` bold `tput sgr0` or `tput rev`invers`tput sgr0` or `tput smul`underline`tput sgr0`"
 bold  or invers or underline

 $ echo "`tput setf 2`green`tput setf 4`red`tput sgr0`"

Farben:

 0 black
 1 blue
 2 green
 3 yellow
 4 red
 5 purple
 6 cyan
 7 grey

calculating with bourne shell

 expr 2048 \* 2
 4096

 let Z=2*2048
 echo $Z
 4096

random numbers with bash

 for (( I=1; i<1000 ; i++));do printf "%.2d.Zahl ist %10d\n" $i $RANDOM;done

Auswahlmenüs auswählen

 select auswahl in Punkt1 Punkt2 Punkt3 Punkt4
 do
     echo "wahl war: $auswahl"
 done

Wait for other processes

 wait 4711

 wait

create user defined SIGNAL

 trap './script' SIGUSR1
 cat script
 ...
 kill -SIGUSR1 $$

job management

 jobs
 fg %jobnr
 bg %jobnr

seq with formated string

 seq -f '%05g' 3
 seq --format='%05g' 3
 00001
 00002
 00003

eval

With eval you can execute a command sequence that is stored in a string like:

 set -x
 LSCMD="ls -lt"
 eval $LSCMD

The set -x enables output where you can see what the shell makes out of the string.

dirname and basename

 dirname /home/user/asdf.txt

 basename /home/user/asdf.txt

 basename /home/user/asdf.txt .txt

ulimit

With ulimit you can set the upper bound for resource use.

 ulimit -a

 ulimit -c 0

 ulimit -f 512000

 ulimit -S -n 250

 ulimit -S -u 100

 ulimit -S -v 50000