chuong 3 - bai 3_ham_vd_mau

7/30/2019 Chuong 3 - Bai 3_ham_vd_mau

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Mc ch

Nm c cch s dng hm

Hiu v s dng cu trc mng Hiu c mt s v d minh ha


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Ni dung

Vit khi lnh

Khai bo v s dng hm (Function) Khai bo v s dng mng Mt s v d v Linux Shell


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S dng cp {} bc khi lnh : if [ -f file_one ] && {

ls -1echo complex block execute }then

#echo command completed fi

Khi lnh { . . . }


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Shell cung cpcho NSD t tohm hay th tc triu gibntrong script.

C php nh nghahm : c 2 cchCch 1: function_name() {

statements

}

Cch 2: function function_name {

statements...

}

Khai bo v s dng hm (Function)


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#!/bin/bashJUST_A_SECOND=1funky (){

echo "This is a simple function."echo "Now exiting simple function."

}

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fun (){ i=0

REPEATS=30echoecho "And now the fun really begins."echosleep $JUST_A_SECOND # Hey, wait a second!

while [ $i lt $REPEATS ] do

echo " let "i+=1"

done}Funky # Now, call the functions.Fun # Now, call the functions.exit 07


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tr v mt gi tr s ta c th dng lnh return : Vd : sum1() {

return 5}

tr v gi tr chui ta c th dng lnh echo : Vd : #!/bin/shsample_func() {

x=5echo Insight sample_func!

}echo Goi su dung ham sample_func

echo $xsample_func

# y=$(sample_func)exit 08


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Binton cc v bin cc b khai bo bin cc b c hiu lc trong hm,

dng t kha local . Nu khng c t kha local, cc bin c

xem l binton cc. Bin ton cc c nhn thyv c th thay i

bi tt c cc hm trong script.

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#!/bin/shsample_text=glocal variable fun1() {

local sample_text=local variable echo function fun1 is executing echo $sample_text

}echo $sample_textfun1echo script ended echo $sample_textexit 0

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Hm v cch truyntham s Truyn tham s cho hm tng t nh

truyntham s trn dng lnh. Vd :

function1() "param1","param2","param3". . .

Bn trong hm s dng cc bin mitrng: $*, $1, $2 ly gi tr cc thams truynvo

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max2 33 34return_val=$?if [ "$return_val" eq $E_PARAM_ERR ]then

echo "Need to pass two parameters to the function."elif [ "$return_val" eq $EQUAL ]

thenecho "The two numbers are equal."

elseecho "The larger of the two numbers is

$return_val."fiexit 0

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VD: S dng bin ton cc v cc b (local)#!/bin/bash# Global and local variables inside a function.func()

{local loc_var=23 # Declared as local variable.echo # Uses the 'local' builtin.echo "\"loc_var\" in function = $loc_var"global_var=999 # Not declared as local.

# Defaults to global.echo "\"global_var\" in function = $global_var"

}

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func# Now,to see if local variable "loc_var"# exists outsidefunction.echoecho "\"loc_var\" outside function = $ loc_var # $loc_var outside function =# No, $loc_var not visible globally.echo "\"global_var\" outside function = $ global_var # $global_var outside function = 999# $global_var is visible globally.echoexit 0

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Khai bo v s dng mng

Phin bn mi ca Bash h tr mng 1 chiu. Mt phn t ca mng c khai bo v khi to nh sau:variable[xx]=values

lygi tr ca 1 phn t trong mng th s dng cu trc sau:

${variable[xx]}

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Khai bo v s dng mng

khai bo 1 mng gi tr, ta s dng cu trcsau:

Cch 1: (c ch s mng l tun t) array=( zero one two three four five )

Cch 2: (gn ch s mng l c th) array_name=( [0]="first element" [1]="second

element [3]="fourth element" )

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Khai bo v s dng mng

Vd1: Khai bo v dng mng n gin #!/bin/bash

area[11]=23area[13]=37

area[51]=UFOsecho -n "area[11] = "echo ${area[11]} # {curly brackets} needed.echo -n "area[13] = "echo ${area[13]}

echo "Contents of area[51] are ${area[51]}. echo -n "area[43] = "echo ${area[43]} (null variable).

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Khai bo v s dng mng

# Sum of two array variables assigned to third area[5]=èxpr ${area[11]} + ${area[13]}ècho "area[5] = area[11] + area[13]"echo -n "area[5] = "echo ${area[5]}area[6]=èxpr ${area[11]} + ${area[51]}ècho "area[6] = area[11] + area[51]"echo -n "area[6] = "echo ${area[6]}# This fails because adding an integer to a

string is not permitted.exit 0

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Khai bo v s dng mng

Bash cho php thc hin thao tc truy cp mng trn cc bin khngkhai bo kiu mng.

string=abcABC123ABCabcecho ${string[@]} # abcABC123ABCabc

echo ${string[*]} # abcABC123ABCabcecho ${string[0]} # abcABC123ABCabcecho ${string[1]} # No output!

# Why?echo ${#string[@]} # 1

# One element in the array.# The string itself.

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Khai bo v s dng mng

# Lines of the text.Line[1]="I do not know which to prefer,"Line[2]="The beauty of inflections"

Line[3]="Or the beauty of innuendoes,"Line[4]="The blackbird whistling"Line[5]="Or just after. for index in 1 2 3 4 5 # Five lines.

doecho -n "${Line[index]}"

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MT S V D

V LINUX SHELL

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1. X l chui

Tr v di ca chui (String Length) C php: 3 cch

${#string} expr length $string expr "$string" : '.*

V d

stringZ=abcABC123ABCabcecho ${#stringZ} # 15echo `expr length $stringZ` # 15echo `expr "$stringZ" : '.*'` # 15

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1. X l chui

Tm di ca chui con khp vi chui string. C php: 2 cch

expr match "$string" '$substring'$substring is a regular expression.

expr "$string" : '$substring'$substring is a regular expression.

V d: stringZ=abcABC123ABCabc

#|| echo `expr match "$stringZ" 'abc[AZ]*.2` # 8 echo `expr "$stringZ" : 'abc[AZ]*.2'` # 8

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1. X l chui

Ly ch s Index ca substring xut hin u tintrong string C php:

expr index $string $substring V d:

stringZ=abcABC123ABCabcecho `expr index "$stringZ" C12` # 6

# C position.echo `expr index "$stringZ" 1c` # 3# 'c' (in #3 position) matches before '1.

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1. X l chui

Ly 1 chui con t 1 chui c sn Cp php

${string:position}Nu position l "*" hoc "@ th s ly ton b chui string.

${string:position:length} V d: stringZ=abcABC123ABCabc# 0123456789.....# 0based indexing. echo ${stringZ:0} # abcABC123ABCabcecho ${stringZ:1} # bcABC123ABCabcecho ${stringZ:7} # 23ABCabcecho ${stringZ:7:3} # 23A

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1. X l chui

Loi b chui con trong chui string C php:

${string#substring} loi b chui con ngn nht trong chui string. Substring l biu thc chnh

qui

${string##substring} loi b chui con di nht trong chui string.

V d:stringZ=abcABC123ABCabc

# || # ||

echo ${stringZ#a*C} # 123ABCabc# Strip out shortest match between 'a' and 'C'.echo ${stringZ##a*C} # abc# Strip out longest match between 'a' and 'C'.

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1. X l chui

Thay th chui C php ${string/substring/replacement} thay th chui con u tin khp vi substring. ${string//substring/replacement}

thay th ton b chui con khp vi substring V d:

stringZ=abcABC123ABCabcecho ${stringZ/abc/xyz} # xyzABC123ABCabc# Replaces first match of 'abc' with 'xyz'.echo ${stringZ//abc/xyz} # xyzABC123ABCxyz

# Replaces all matches of 'abc' with # 'xyz'.

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2. S dng cc bin tham s

Vi d: your_id=${USER}on${HOSTNAME}

echo "$your_id"

echo "Old \$PATH = $PATH"PATH=${PATH}:/opt/bin #Add /opt/bin to$PATH for duration of script.

echo "New \$PATH = $PATH"

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3. S dng declare

Phin bn Bash 2 hoc mi hn, h thng h tr tnhnng qui nh kiu cho bin. s dng chc nng ny, ta kho s cc tham s ty chn sau

r readonlydeclare r var1(declare r var1 works the same as readonly var1)

readonly variable fails with an error message.

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3. S dng declare

i integer declare i number # The script will treat subsequent occurrences of "number" as an integer.number=3echo "Number = $number" # Number = 3

number=threeecho "Number = $number" # Number = 0# Tries to evaluate the string "three" as an integer.Certain arithmetic operations are permitted for declared integer variables without the

need for expr or let.n=6/3

echo "n = $n" # n = 6/3declare i n n=6/3echo "n = $n" # n = 2

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3. S dng declare

a array declare a indices The variable indices will be treated as an array.

f function(s)

declare f function_name A declare f function_name in a script lists just the function named.

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3. S dng declare

#!/bin/bashdeclare f # Lists the function above. echodeclare i var1 # var1 is an integer. var1=2367echo "var1 declared as $var1"var1=var1+1 # Integer declaration eliminates the need for 'let'.echo "var1 incremented by 1 is $var1."# Attempt to change variable declared as integer.echo "Attempting to change var1 to floating point value, 2367.1."var1=2367.1 # Results in error message, with no change to variable.echo "var1 is still $var1"echodeclare r var2=13.36 # 'declare' permits setting a variable property

#+ and simultaneously assigning it a value.echo "var2 declared as $var2" # Attempt to change readonly variable.var2=13.37 # Generates error message, and exit from script.echo "var2 is still $var2" # This line will not execute.exit 0 # Script will not exit here.

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4. Tham chiu gin tip 1 bin

Assume that the value of a variable is the name of a second variable. Is it somehow possible toretrieve the

value of this second variable from the first one? For example, if a=letter_of_alphabet andletter_of_alphabet=z, can a reference to a return z?This can indeed be done, and it is called anindirect reference. It uses the unusual evalvar1=\$$var2 notation.

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4. Tham chiu gin tip 1 bin . Indirect References#!/bin/bash# indref.sh: Indirect variable referencing. # Accessing the contents of the contents of a variable.a=letter_of_alphabet # Variable "a" holds the name of another variable.letter_of_alphabet=zecho# Direct reference.echo "a = $a" # a = letter_of_alphabet# Indirect reference.eval a=\$$aecho "Now a = $a" # Now a = z

echo# Now, let's try changing the secondorder reference. t=table_cell_3table_cell_3=24echo "\"table_cell_3\" = $table_cell_3" # "table_cell_3" = 24echo n "dereferenced \"t\" = "; eval echo \$$t # dereferenced "t" = 24# In this simple case, the following also works (why?).# eval t=\$$t; echo "\"t\" = $t"echot=table_cell_3NEW_VAL=387table_cell_3=$NEW_VALecho "Changing value of \"table_cell_3\" to $NEW_VAL."echo "\"table_cell_3\" now $table_cell_3"echo n "dereferenced \"t\" now "; eval echo \$$t# "eval" takes the two arguments "echo" and " \$$t" (set equal to $table_cell_3)echo# (Thanks, Stephane Chazelas, for clearing up the above behavior.)# Another method is the ${!t} notation, discussed in "Bash, version 2" section.# See also ex78.sh.exit 0

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5. Hm $RANDOM: pht sinh integer

$RANDOM : in the range 0 32767. #!/bin/bash# $RANDOM returns a different random integer at each invocation.# Nominal range: 0 32767 (signed 16bit integer). MAXCOUNT=10count=1

echoecho "$MAXCOUNT random numbers:"echo "" while [ "$count" le $MAXCOUNT ] # Generate 10 ($MAXCOUNT) random integers. do

number=$RANDOMecho $number let "count += 1" # Increment count.

doneecho "" # If you need a random int within a certain range, use the 'modulo' operator.# This returns the remainder of a division operation.exit 0

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#!/bin/bash# pickcard.sh # This is an example of choosing random

elements of an array.# Pick a card, any card.Suites="ClubsDiamonds

HeartsSpades"

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Denominations="2345678910JackQueenKingAce"# Note variables spread over multiple lines.38


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suite=($Suites) # Read into array variable.denomination=($Denominations)num_suites=${#suite[*]} # Count how many elements.num_denominations=${#denomination[*]}

echo n"${denomination[$((RANDOM%num_denominations))]} of"

echo ${suite[$((RANDOM%num_suites))]}exit 0

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Summary

Khai bo v s dng hm (Function) Khai bo v s dng mng

Mt s v d v Linux Shell

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chuong 3 - bai 3_ham_vd_mau

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