1. Re ad and Write File s
w ith Pe rl
Pao lo Marc atili - Pro grammazio ne 08-09

2. Age nda
> Pe rl I
O
> Ope n a File
> Write o n File s
> Re ad fro m File s
> While lo o p
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Pao lo Marc atili - Pro grammazio ne 08-09

3. Pe rl I
O
(I me ans I
O nput/Output)
Pao lo Marc atili - Pro grammazio ne 08-09

4. Why I
O?
S inc e no w , Pe rl is
#! /us r/bin/pe rl -w
us e s tric t; <- ALWAYYYYYS S S S !!!
my $ s tring=quot;I lo ve to mato e s !nquot;;
fo r (my $ i=1 ;$ i<1 00;$ i++){
print $ s tring;
}
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Pao lo Marc atili - Pro grammazio ne 08-09

5. Why I
O?
But if w e w ant to do the s ame
w ith a us e r-s ubmitte d s tring?
5
Pao lo Marc atili - Pro grammazio ne 08-09

6. Why I
O?
But if w e w ant to do the s ame
w ith a us e r-s ubmitte d s tring?
I c an do this !
O
6
Pao lo Marc atili - Pro grammazio ne 08-09

7. I type s
O
Main I nputs
> Ke ybo ard
> File
> Erro rs
Main o utputs
> Dis play
> File
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Pao lo Marc atili - Pro grammazio ne 08-09

8. Mo re than to mato e s
Le t’s try it:
#! /us r/bin/pe rl -w
us e s tric t; my
$ s tring=<S T N>;fo r (my $ i=1 ;$ i<1 00;$ i+
DI
+){print $ s tring;}
8
Pao lo Marc atili - Pro grammazio ne 08-09

9. Ratio nale
Re ad fro m and w rite to diffe re nt me dia
S T N me ans s tandard input (ke ybo ard)
DI
^
this is a handle
<S MT me ans
H>
“re ad fro m the s o urc e c o rre s po nding to handle SMTH”
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Pao lo Marc atili - Pro grammazio ne 08-09

10. Handle s
Handle s are jus t s tre ams “nic kname s ”
S o me o f the m are fixe d:
ST NDI <-de fault is ke ybo ard
ST DOUT <-de fault is dis play
ST DERR <-de fault is dis play
S o me are us e r de fine d (file s )
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Pao lo Marc atili - Pro grammazio ne 08-09

11. Ope n/Write a file
Pao lo Marc atili - Pro grammazio ne 08-09

12. o pe n
We have to c re ate a handle fo r o ur file
o pe n(OUT “>o ut.txt”) o r die (“Erro r o pe ning o ut.txt: $ !”);
,
^
N.B. : it’s us e r de fine d, yo u de c ide it
Tip
“<o ut.txt” <- re ad fro m o ut.txt
“>o ut.txt” <- w rite into o ut.txt
“>>o ut.txt” <- appe nd to o ut.txt
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Pao lo Marc atili - Pro grammazio ne 08-09

13. c lo s e
Whe n finis he d w e have to c lo s e it:
c lo s e OUT;
I yo u do nt, Santa will bring no gift.
f
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Pao lo Marc atili - Pro grammazio ne 08-09

14. Print OUT
#! /us r/bin/pe rl -w
us e s tric t;
o pe n(OUT quot;>o ut.txtquot;) || die (quot;Erro r o pe ning o ut.txt: $ !quot;);
,
print quot;type yo ur c laim:nquot;;
my $ s tring=<ST N>;DI
fo r (my $ i=1 ;$ i<1 00;$ i++){
print OUT $ s tring;
}
c lo s e OUT ;
No w le t’s play w ith <,>,>> and file pe rmis s io ns
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Pao lo Marc atili - Pro grammazio ne 08-09

15. Re ad fro m File s
Pao lo Marc atili - Pro grammazio ne 08-09

16. Re ad
o pe n(I “<s o ng.txt”) o r die (“Erro r o pe ning s o ng.txt: $ !”);
N,
print <IN>;
print <IN>;
print <I
N>;
print <I
N>;
print <I
N>;
print <I
N>;
print <I
N>;
print <I
N>;
print <I
N>;
print <I
N>;
print <I
N>;
print <I
N>;
print <I
N>;
print <I
N>;
c lo s e I
N;
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Pao lo Marc atili - Pro grammazio ne 08-09

17. Re ad w ith lo o ps
Pro ble ms :
> I lo ng
t’s
> File s ize unkno w n
s o lutio n:
Us e lo o ps
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Pao lo Marc atili - Pro grammazio ne 08-09

18. While lo o p
Pao lo Marc atili - Pro grammazio ne 08-09

19. While
w hile (c o nditio n){
do s o me thing…
}
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Pao lo Marc atili - Pro grammazio ne 08-09

20. While - fo r diffe re nc e s
While Fo r
> Unde te rmine d > De te rmine d
> No c o unte r > Co unte r
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Pao lo Marc atili - Pro grammazio ne 08-09

21. While e xample
Appro x. s o lutio n o f x^2-2=0
my $ e rr=1 ;
my $ s o l=0;
w hile ($ e rr>.1 ){
$ s o l+=.0001 ;
$ e rr=$ s o l**2-2;
}
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Pao lo Marc atili - Pro grammazio ne 08-09

22. Re ad w ith w hile
#! /us r/bin/pe rl -w
us e s tric t;
o pe n(MOD, quot;<I G.pdbquot;) || die (quot;Erro r o pe ning
IG.pdb: $ !quot;);
while (my $ line =<MOD>){
print s ubs tr($ line ,0,6).quot;nquot;;
}
c lo s e MOD;
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Pao lo Marc atili - Pro grammazio ne 08-09

23. Re dire c t o utputs
Pao lo Marc atili - Pro grammazio ne 08-09

24. Re dire c tio ns
#!/us r/bin/pe rl
o pe n(ST DOUT quot;>fo o .o utquot;) || die quot;Can't re dire c t s tdo utquot;;
,
o pe n(ST DERR, quot;>& DOUT || die quot;Can't dup s tdo utquot;;
ST quot;)
s e le c t(STDERR); $ | = 1 ; # make unbuffe re d
s e le c t(STDOUT $ | = 1 ;
); # make unbuffe re d
c lo s e (STDOUT);
c lo s e (STDERR);
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