Bash-Beginners-Guide

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Bash Guide for Beginners bzip2 /var/tmp/home_franky.tar # Copy the file to another host - we have ssh keys for making this work without intervention. scp /var/tmp/home_franky.tar.bz2 bordeaux:/opt/backup/franky > /dev/null 2>&1 # Create a timestamp in a logfile. date >> /home/franky/log/home_backup.log echo backup succeeded >> /home/franky/log/home_backup.log First of all, you are more likely to make errors if you name files and directories manually each time you need them. Secondly, suppose franky wants to give this script to carol, then carol will have to do quite some editing before she can use the script to back up her home directory. The same is true if franky wants to use this script for backing up other directories. For easy recycling, make all files, directories, usernames, servernames etcetera variable. Thus, you only need to edit a value once, without having to go through the entire script to check where a parameter occurs. This is an example: #!/bin/bash # This script makes a backup of my home directory. # Change the values of the variables to make the script work for you: BACKUPDIR=/home BACKUPFILES=franky TARFILE=/var/tmp/home_franky.tar BZIPFILE=/var/tmp/home_franky.tar.bz2 SERVER=bordeaux REMOTEDIR=/opt/backup/franky LOGFILE=/home/franky/log/home_backup.log cd $BACKUPDIR # This creates the archive tar cf $TARFILE $BACKUPFILES > /dev/null 2>&1 # First remove the old bzip2 file. Redirect errors because this generates some if the archive # does not exist. Then create a new compressed file. rm $BZIPFILE 2> /dev/null bzip2 $TARFILE # Copy the file to another host - we have ssh keys for making this work without intervention. scp $BZIPFILE $SERVER:$REMOTEDIR > /dev/null 2>&1 # Create a timestamp in a logfile. date >> $LOGFILE echo backup succeeded >> $LOGFILE Large directories and low bandwidth The above is purely an example that everybody can understand, using a small directory and a host on the same subnet. Depending on your bandwidth, the size of the directory and the location of the remote server, it can take an awful lot of time to make backups using this mechanism. For larger directories and lower bandwidth, use rsync to keep the directories at both ends synchronized. 3.3. Quoting characters Chapter 3. The Bash environment 44
Bash Guide for Beginners 3.3.1. Why? A lot of keys have special meanings in some context or other. Quoting is used to remove the special meaning of characters or words: quotes can disable special treatment for special characters, they can prevent reserved words from being recognized as such and they can disable parameter expansion. 3.3.2. Escape characters Escape characters are used to remove the special meaning from a single character. A non-quoted backslash, \, is used as an escape character in Bash. It preserves the literal value of the next character that follows, with the exception of newline. If a newline character appears immediately after the backslash, it marks the continuation of a line when it is longer that the width of the terminal; the backslash is removed from the input stream and effectively ignored. franky ~> date=20021226 franky ~> echo $date 20021226 franky ~> echo \$date $date In this example, the variable date is created and set to hold a value. The first echo displays the value of the variable, but for the second, the dollar sign is escaped. 3.3.3. Single quotes Single quotes ('') are used to preserve the literal value of each character enclosed within the quotes. A single quote may not occur between single quotes, even when preceded by a backslash. We continue with the previous example: franky ~> echo '$date' $date 3.3.4. Double quotes Using double quotes the literal value of all characters enclosed is preserved, except for the dollar sign, the backticks (backward single quotes, ``) and the backslash. The dollar sign and the backticks retain their special meaning within the double quotes. The backslash retains its meaning only when followed by dollar, backtick, double quote, backslash or newline. Within double quotes, the backslashes are removed from the input stream when followed by one of these characters. Backslashes preceding characters that don't have a special meaning are left unmodified for processing by the shell interpreter. A double quote may be quoted within double quotes by preceding it with a backslash. franky ~> echo "$date" 20021226 Chapter 3. The Bash environment 45
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Page 9 and 10: Introduction 1. Why this guide? The
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Page 15 and 16: Bash Guide for Beginners mia:~> cat
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Page 19 and 20: More information about the file des
Page 21 and 22: Built-in commands are necessary to
Page 23 and 24: • Brace expansion • Tilde expan
Page 25 and 26: A number of methods can be used; on
Page 27 and 28: Bash Guide for Beginners stop in ea
Page 29 and 30: Chapter 2. Writing and debugging sc
Page 31 and 32: the documentation of your favorite
Page 33 and 34: Bash Guide for Beginners Comments a
Page 35 and 36: Bash Guide for Beginners + set +x I
Page 37 and 38: Chapter 3. The Bash environment In
Page 39 and 40: Bash Guide for Beginners local pid
Page 41 and 42: MOZILLA_FIVE_HOME=/usr/lib/mozilla
Page 43 and 44: Bash Guide for Beginners franky ~>
Page 45 and 46: the GNU Awk programming language is
Page 47 and 48: Bash Guide for Beginners 3.2.4. Res
Page 49 and 50: LINES MACHTYPE MAILCHECK OLDPWD OPT
Page 51: two is the second positional parame
Page 55 and 56: A correctly-formed brace expansion
Page 57 and 58: Bash Guide for Beginners If the sub
Page 59 and 60: of the whitespace characters "space
Page 61 and 62: Bash Guide for Beginners /dev/hda5
Page 63 and 64: Bash Guide for Beginners 3.7. Summa
Page 65 and 66: Two regular expressions may be conc
Page 67 and 68: LABEL=/ / ext3 defaults 1 1 If this
Page 69 and 70: cathy ~> ls -ld [[:digit:]]* drwxrw
Page 71 and 72: Bash Guide for Beginners p Print te
Page 73 and 74: sandy ~> sed -n '/a text/,/This/p'
Page 75 and 76: Bash Guide for Beginners # This is
Page 77 and 78: Chapter 6. The GNU awk programming
Page 79 and 80: Bash Guide for Beginners 121script.
Page 81 and 82: Bash Guide for Beginners amd.conf a
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Page 87 and 88: Chapter 7. Conditional statements I
Page 89 and 90: Bash Guide for Beginners Table 7-2.
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Page 93 and 94: [root@elegance root]# We switch to
Page 95 and 96: Bash Guide for Beginners echo "Prop
Page 97 and 98: Bash Guide for Beginners We use the
Page 99 and 100: Bash Guide for Beginners case EXPRE
Page 101 and 102: Upon successful condition testing,
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Bash Guide for Beginners bit better
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8.2. Catching user input 8.2.1. Usi
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Bash Guide for Beginners michel ~/t
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Bash Guide for Beginners # DO NOT E
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File descriptor 5 Bash Guide for Be
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Bash Guide for Beginners The result
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Bash Guide for Beginners ♦ Compre
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Bash Guide for Beginners for i in `
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touch pic-`date +%s`.jpg sleep 300
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DISKFUL=$(df -h $WEBDIR | grep -v F
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;; 2) $FORTUNE startrek ;; 3) $FORT
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[carol@octarine ~/test] ls -a ./ ..
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Bash Guide for Beginners 9.7.2. Exa
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Chapter 10. More on variables In th
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Bash Guide for Beginners [bob in ~]
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if [ -z $1 ]; then echo "Usage: $0
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10.3.3. Transformations of variable
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Bash Guide for Beginners The opposi
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Chapter 11. Functions In this chapt
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The commands after && are only exec
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zip2 "$TAR" echo "...done." >> "$LO
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Chapter 12. Catching signals In thi
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Bash Guide for Beginners maud: ~> k
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Bash Guide for Beginners 2. Write a
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Bash Guide for Beginners jobs kill
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if [ $i -eq 5 ] ArrowUp+Enter or !!
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cd Change directory. cdp/cdplay An
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Bash Guide for Beginners gimp grep
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Send and receive mail. man Read man
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Bash Guide for Beginners rsh RPM Pa
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W Bash Guide for Beginners w Show w
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Index A aliases Section 3.5.1 ANSI-
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Bash Guide for Beginners Section 3.
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J Bash Guide for Beginners K kill k
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eadonly Section 10.1.3 regular expr
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Bash Guide for Beginners vi(m) Sect
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