Dodatek do wykładu 3

Substring

${string:position}

${string:position:length}

Przykład

$ cat substr.sh

#! /bin/bash

var="Welcome to the geekstuff"

echo ${var:15}

echo ${var:15:4}

$ ./substr.sh

geekstuff

geek

Dopasowywanie najkrótszego łańcucha (z przodu)

${string#substring}

Dopasowywanie najkrótszego łańcucha (z tyłu)

${string%substring}

Przykład

$ cat shortest.sh

#! /bin/bash

filename="bash.string.txt"

echo ${filename#*.}

echo ${filename%.*}

$ ./shortest.sh

After deletion of shortest match from front: string.txt

After deletion of shortest match from back: bash.string

Dopasowywanie najdłuższego łańcucha (z przodu)

${string##substring}

Dopasowywanie najdłuższego łańcucha (z tyłu)

${string%%substring}

Przykład

$ cat longest.sh

#! /bin/bash

filename="bash.string.txt"

echo "After deletion of longest match from front:" ${filename##*.}

echo "After deletion of longest match from back:" ${filename%%.*}

$ ./longest.sh

After deletion of longest match from front: txt

After deletion of longest match from back: bash

Znajdowanie, dopasowywanie i zamiana (1)

${string/pattern/replacement}

Przykład zamiany tylko pierwszego

$ cat firstmatch.sh

#! /bin/bash

filename="bash.string.txt"

echo "After Replacement:" ${filename/str*./operations.}

$ ./firstmatch.sh

After Replacement: bash.operations.txt

Znajdowanie, dopasowywanie i zamiana (ALL)

${string//pattern/replacement}

Przykład zamiany wszystkich

$ cat allmatch.sh

#! /bin/bash

filename="Path of the bash is /bin/bash"

echo "After Replacement:" ${filename//bash/sh}

$ ./allmatch.sh

After Replacement: Path of the sh is /bin/sh

Znajdowanie, dopasowywanie i zamiana (FIRST)

${string/#pattern/replacement}

Znajdowanie, dopasowywanie i zamiana (LAST)

${string/%pattern/replacement}

Przykład

$ cat posmatch.sh

#! /bin/bash

filename="/root/admin/monitoring/process.sh"

echo "Replaced at the beginning:" ${filename/#\/root/\/tmp}

echo "Replaced at the end": ${filename/%.*/.ksh}

$ ./posmatch.sh

Replaced at the beginning: /tmp/admin/monitoring/process.sh

Replaced at the end: /root/admin/monitoring/process.ksh

Brace Expansion

Tworzymy wiele z “jednego”

$ echo last{mce,boot,xorg}.log

lastmce.log lastboot.log lastxorg.log

where last is Preamble and .log is the postscript

Przykład:

$ cat bkup.sh

set -x # expand the commands

da=`date +%F`

cp $da.log{,.bak}

$ ./bkup.sh

++ date +%F

+ da=2010-05-28

+ cp 2010-05-28.log 2010-05-28.log.bak

Przykład:

$ cat restore.sh

set -x # expand the commands

da=`date +%F`

cp $da.log{.bak,}

$ ./restore.sh

++ date +%F

+ da=2010-05-28

+ cp 2010-05-28.log.bak 2010-05-28.log

Przykład:

$ cat expand.sh

echo {oct,hex,dec,bin}

$ ./expand.sh

oct hex dec bin

Sekwencje

Przykład:

$ cat sequence.sh

cat /var/log/messages.{1..3}

echo {a..f}{1..9}.txt

$ ./sequence.sh

May 9 01:18:29 x3 ntpd[2413]: time reset -0.132703 s

May 9 01:22:38 x3 ntpd[2413]: synchronized to LOCAL(0), stratum 10

May 9 01:23:44 x3 ntpd[2413]: synchronized to

May 9 01:47:48 x3 dhclient: DHCPREQUEST on eth0

May 9 01:47:48 x3 dhclient: DHCPACK from 23.42.38.201

..

a1.txt a2.txt a3.txt a4.txt a5.txt a6.txt a7.txt a8.txt a9.txt b1.txt b2.txt b3.txt b4.txt b5.txt b6.txt b7.txt b8.txt b9.txt c1.txt c2.txt c3.txt c4.txt c5.txt c6.txt c7.txt c8.txt c9.txt d1.txt d2.txt d3.txt d4.txt d5.txt d6.txt d7.txt d8.txt d9.txt e1.txt e2.txt e3.txt e4.txt e5.txt e6.txt e7.txt e8.txt e9.txt f1.txt f2.txt f3.txt f4.txt f5.txt f6.txt f7.txt f8.txt f9.txt

Sekwencje inkrementowalne

Syntax:

<start>..<end>..<incr>

Przykład

$ echo /var/log/messages.{1..7..2}

/var/log/messages.1 /var/log/messages.3 /var/log/messages.5 /var/log/messages.7

$

Pitfall

$ A=2

$ echo /var/log/messages.{1..7..$A}

/var/log/messages.{1..7..2}

$