Bash Scripting

Bash Scripting
➢ Кaкво е това нещо bash
➢ За какво може да се използва
➢ Как да разберем кога нещо не е за bash

Bash Scripting
Ресурси от където можете да започнете
➢ http://www.tldp.org/HOWTO/
Bash-Prog-Intro-HOWTO.html
--- man bash ---
➢ Advanced bash scripting
http://www.tldp.org/LDP/abs/html/

Bash Scripting
Прост скрипт на bash
#!/bin/bash
STR="Hello World!"
echo $STR

Bash Scripting
Какво ни е нужно за да си
напишем хубав скрипт
➢ ясно дефиниране на задачата
➢ познаване на командите които ще ползвате
за да се свърши задачата
➢ свободно време :)

Bash Scripting
Видове скриптове
➢ one line
ps aux|grep root|awk '{print $2}'
➢ multiline
string='2'
let string++
echo $string

Bash Scripting
Variables
➢ export, typeset, declare, readonly
➢ local, global
function x {
local USER='root'
}

Bash Scripting
Variables deference
➢ $a
➢ file_no$a
➢ $afile_no – does not work :)
➢ ${a}file_no – this is the way to do it

Bash Scripting
File descriptors(std=standard):
stdin – uses pipe or <
stdout – uses >
stderr – uses 2>

Bash Scripting
Какво можете да правите с тези file descriptor-и:
1. redirect stdout to a file
( ls -l > ls-l.txt )
2. redirect stderr to a file
( grep da * 2> grep-errors.txt )
3. redirect stdout to a stderr
( grep da * 1>&2 )
4. redirect stderr to a stdout
( grep * 2>&1 )
5. redirect stderr and stdout to a file
( rm -f $(find / -name core) &> /dev/null )

Bash Scripting
Pipes
ls -l | grep aha
ps aux | grep userx | awk '{print $2}'
cat filename | sed 's/krava/mlqko/g'

Bash Scripting
#!/bin/bash
tar -cfz /usr/local/backup/my-backup-today.tgz
/home/me
#!/bin/bash
dir='/usr/local/backup'
file=$dir/my-backup-$(date+%Y%m%d).tgz
tar -cfz $file /home/me

Bash Scripting
debuging
най дорият начин:
#!/bin/bash -x
за големи скриптове
echo или read

Bash Scripting
Контролни структори
if-then-else
if-then-elif-then-elif-then-else
select-in
case-in
for-do
while-do
until-do

Bash Scripting
if-then-else
if [ “$1” == '' ]; then
echo “Usage: $0 variable”
else
make_me_stop
fi
if ( ! ps ax | grep kuku > /dev/null ); then
echo “KUKU not found!”
fi

Bash Scripting
Difference in parenthesis
( ) - executes commands in new shell
{ } - executes commands in the current shell
(( )) - arithmetic expressions
[ ] - basic integer arithmetic, basic string comparison
and file attributes checks
[[ ]] - basic integer arithmetic, regular expressions and
file attributes checks

Bash Scripting
if-then-elif-then-else
if [ "$1" == 'weekly' ]; then
table_list=$(<tables.weekly)
elif [ "$1" == 'daily' ]; then
table_list=$(<tables.daily)
else
table_list=$(<tables.hourly)
fi
tables=''
for table in $table_list; do tables="$tables $table"; done
mysqldump --compact -e -t -q -R --single-transaction blog_db
$tables

Bash Scripting
case-in
case “$1” in
'start')
make_me_stop ;;
'stop')
make_me_start ;;
*)
echo “Usage: $0 variable” ;;
esac

Bash Scripting
for-do
for var in `seq 1 10`; do
echo -n “$var “
done
Ето какво ще изведе това:
1 2 3 4 5 6 7 8 9 10
for file in /bin/*; do
echo $file
done
Това е еквивалентно на ls -1A /bin

Bash Scripting
while-do
count=0;
while(true); do
let count++;
if [ “$count” == “10” ]; then
exit 0;
fi
done

Bash Scripting
functions
function fixme {
echo $0 $1 $2 $3
}
Как викаме функция
# ./fixme a j k
./fixme a j k
#

Bash Scripting
Bash regular expressions
#!/bin/bash
regex=$1
if [[ $1 =~ $regex ]]; then
echo “$2 matched”
else
echo “$2 NOT matched”
fi
# ./regex search searchstring
searchstring matched

Bash Scripting
Bash substitutions
#!/bin/bash
for i in /dir/*; do
echo ${i/.*/}
done
$ ls *.pl *.txt
collect-plans.pl cpu-abuse.pl landing.txt ap_write.txt
$ ./script
collect-plans
cpu-abuse
landing
ap_write

Bash Scripting
Bash substitutions
Inside ${ ... } Action taken
name:number:number Substring starting character,
length
#name Return the length of the
string
name#pattern Remove (shortest)
front-anchored pattern
name##pattern Remove (longest)
front-anchored pattern

Bash Scripting
Bash substitutions
Inside ${ ... } Action taken
name%pattern Remove (shortest)
rear-anchored pattern
name%%pattern Remove (longest)
rear-anchored pattern
name/pattern/string Replace first occurrence
name//pattern/string Replace all occurrences

Bash Scripting
Bash substitutions
hackman@terion:~$ a='123456'
hackman@terion:~$ echo ${a:3:5}
456
hackman@terion:~$ echo ${a:1:4}
2345
hackman@terion:~$ echo ${#a}
6

Bash Scripting
Bash substitutions (front)
hackman@terion:~$ a='grizzly.yuhu.biz'
hackman@terion:~$ echo ${a#*.}
yuhu.biz
hackman@terion:~$ echo ${a##*.}
biz

Bash Scripting
Bash substitutions (rear)
hackman@terion:~$ a='grizzly.yuhu.biz'
hackman@terion:~$ echo ${a%.*}
grizzly.yuhu
hackman@terion:~$ echo ${a%%.*}
grizzly

Bash Scripting
Bash substitutions (regexp)
hackman@terion:~$ a='pate.pate.patence.txt'
hackman@terion:~$ echo ${a/pate/kate}
kate.pate.patence.txt
hackman@terion:~$ echo ${a//pate/kate}
kate.kate.katence.txt

Bash Scripting
Bash arrays
#!/bin/bash #!/bin/bash
a=(x y z) a=(x y z)
echo ${a[0]} echo ${#a[*]}
echo ${a[1]} # ./array
echo ${a[2]} 3
# ./array
x
y
z

Bash Scripting
Parameter expansion
$ function am() { for i in "$*"; do echo ”$i”; done }
$ am jo ji ko
“jo ji ko”
$ function am() { for i in "$@"; do echo ”$i”; done }
$ am jo ji ko
“jo”
“ji”
“ko”

Bash Scripting
Bash arrays
#!/bin/bash #!/bin/bash
a=(x y z) a=(x y z)
for i in “${a[*]}”; do for i in “${a[@]}”; do
# ./array # ./array
x y z x
y
z

Bash Scripting
Bash special variables
$0 - the name of the script or shell
$# - number of parameters/arguments
$! - PID of the last executed background command
$? - exit status of the last executed command
$* - expands to a single quoted word
$@ - expands to separate words
$- - current bash flags/options
IFS - internal field separator

Bash Scripting
Bash arrays
hackman@gamelon:~$ ip a l eth0|grep 'inet '
inet 10.2.0.3/24 brd 10.2.0.255 scope global eth0
hackman@gamelon:~$ ip=($(ip a l eth0|grep 'inet '))
hackman@gamelon:~$ echo ${ip[0]}
inet
hackman@gamelon:~$ echo ${ip[1]}
10.2.0.3/24

Bash Scripting
Command execution
ip=( $( ip a l eth0|grep 'inet ' ) )
vs.
ip=( ` ip a l eth0|grep 'inet ' ` )

Bash Scripting
? ? ? ? ? ?
? ? ? ?
? ? ? ? ?
? ? ? Въпроси ? ?
?
? ? ? ? ? ?
? ? ? ? ? ? ?
? ? ? ? ? ? ?
Мариян Маринов(HackMan) mm@yuhu.biz

Bash Scripting

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Bash Scripting