Lm quen vi SED -StreamEDitorStream EDitor - sed - l mt trnh son
tho khng tng tc c h tr trn rt nhiu h thng Unix/Linux. N thc hin
thng dch mt script v thc hin cc action trong script . sed l mt tin
ch dng lung (stream) bi cng ging nh nhiu chng trnh Unix khc, input
s i t input stream ti chng trnh ri i ra standard output
stream.Input c th n t mt file hoc ti t pipe hoc thm ch trc tip t
standard input. Output ca sed c th i ti standard output hoc nh hng
ti 1 file hoc ti mt pipe no .1. c trng v th mnh ca SED- chnh sa t
ng mt hoc nhiu file- n gin ha cc thao tc chnh lp i lp li trn nhiu
file- cho php vit cc chng trnh chuyn i hu dng2. Cch thc hot ng ca
SEDSED lm vic trn tng dng trong file text do chu trnh x l ca n s nh
sau:- mi dng c copy vo mt vng nh m "pattern space" ni s din ra cc
thao tc x l- cc lnh chnh sa trong script c thc thi- cc lnh c x l
trn tt c cc dng tr khi mt dng no khng tha mn- nu mt lnh thc hin
thay i input, do cc lnh ch lm vic trn pattern space do d liu thc s
s khng cn l ca input ban u- file input thc cht khng b thay i m cc
thay i ch din ra trn mt bn sao ca n pattern space. Bn copy ny s gi
ti standard output (mc nh)- sed cng s dng mt vng nh m ring "hold
space" c kh nng lu d liu cho cc thao tc truy xut sau .3. C php dng
lnhC php ca SED c th hai dng nh sau:sed [-n] [-e] 'command'
file(s)sed [-n] -f script_file(s)Cc dng ny c th s dng phi hp vi
nhau. Nu nh khng c file input no c ch nh th mc nh sed s c d liu t
standard input.[-n] : ty chn ny ch nh sed khng hin th kt qu ra
standard output nh mc nh. Trong trng hp c php th hai, ta c th t dng
u tin c ni dung#ncng s cho kt qu tng t.4. C php cc lnh ca sedCc lnh
SED c mt c php tng qut nh sau:[address[,address]][!]command
[arguments]SED sao chp tng dng input file vo pattern space, ch th
ca sed bao gm cc address ( address pattern) v cc cu lnh thao tc
(command). Nu mt address khp vi mt dng no trong pattern space th
lnh tng ng s c p dng.1. pattern addressing (nh v mu)Mt lnh sed c th
ch nh 0, 1 hoc nhiu cc address. Address lm nhim v ch th v tr dng m
cc lnh s c thc thi. Mt address c th l mt ch s dng, mt k hiu dng cui
$ hay l mt biu thc chnh quy c bao gi trong cm /pattern/. Ngoi ra, k
hiu \n c th khp vi bt k du xung dng no trong pattern space tr du
xung dng cui pattern space.Nu pattern space cha ...Th lnh s c p dng
cho ...
Khng cha patternp dng cho tng dng trong input
Cha 1 patternAp dng cho tng dng so khp c vi pattern. Mt s lnh ch
chp nhn 1 pattern nha, i , r, q, =
Cha hai pattern cch nhau bng du phyBt u t dng u tin khp v tt c
cc dng khp pattern u tin cho n dng khp pattern th hai
Mt pattern theo sau bi k t !Cc dng khng cha pattern
2. V d:CommandHnh ng c thc hin
s/xx/yy/gThay th ton b xx bi yy trong cc dng (g: global)
/BSD/dXa tt c cc dng c cha BSD
/^BEGIN/,/^END/pIn tt c ni dung nm gia BEGIN v END, tnh c hai mc
ny
/SAVE/!dXa tt c cc dng khng cha t SAVE
/BEGIN/,/END/!s/xx/yy/gThay th tt c xx bi yy trn cc dngkhng nm
trong on BEGIN ti END
Cp ngoc { } c th c dng nhng mt pattern vo trong mt pattern khc
hoc dng p dng nhiu lnh ln mt mu khp vi pattern. Tuy nhin, cn ch
rng, du m ngoc phi nm cui dng ca n v du ng ngoc phi nm c lp trn 1
dng v gia chng khng c khong trng. V d:
5. Nhm cc lnh c bn km minh ha s dng1. Nhm cc lnh chnh sa c
bnLnhM tV d
a\Append, thm vo sau mt dng khp vi address
c\Thay th text (thng l mt khi text)
dXa cc dng
sThc hin cc php thay th (substitution)
2. Cc lnh lin quan ti thng tin ca dng vn bn hin thiLnhM tV d
=Hin th dng ang c
lHin th cc k t iu khin trong ASCII
pPrint - in dng ang c
3. Nhm cc lnh x l input/outputLnhM tV d
nB qua dng hin thi, chuyn ti dng tip theo
rc ni dung t mt file khc vo input stream
wGhi cc dng trong input vo mt file khc
qThot khi sed script, khng sinh thm output no na
