Arithmetic operators
@@ -868,7 +862,7 @@ Thu Feb 6 10:06:20 CET 2003
+ and -addition, subtraction<< and >>left and right bitwise shifts<=, >=, < and >comparison operators
-== and !==equality and inequality
+== and !=equality and inequality&bitwise AND^bitwise exclusive OR|bitwise OR
@@ -904,7 +898,7 @@ leading 0x or 0X denotes hexadecimal. Otherwise,
Word splittingThe shell scans the results of parameter expansion, command substitution, and arithmetic expansion that did not occur within double quotes for word splitting.
-The shell treats each character of $IFS as a delimiter, and splits the results of the other expansions into words on these characters. If IF is unset, or its value is exactly '<space><tab><newline>', the default, then any sequence of IFS characters serves to delimit words. If IFS has a value other than the default, then sequences of the whitespace characters space and Tab are ignored at the beginning and end of the word, as long as the whitespace character is in the value of IFS (an IFS whitespace character). Any character in IFS that is not IFS whitespace, along with any adjacent IF whitespace characters, delimits a field. A sequence of IFS whitespace characters is also treated as a delimiter. If the value of IFS is null, no word splitting occurs.
+The shell treats each character of $IFS as a delimiter, and splits the results of the other expansions into words on these characters. If IFS is unset, or its value is exactly '<space><tab><newline>', the default, then any sequence of IFS characters serves to delimit words. If IFS has a value other than the default, then sequences of the whitespace characters space and Tab are ignored at the beginning and end of the word, as long as the whitespace character is in the value of IFS (an IFS whitespace character). Any character in IFS that is not IFS whitespace, along with any adjacent IF whitespace characters, delimits a field. A sequence of IFS whitespace characters is also treated as a delimiter. If the value of IFS is null, no word splitting occurs.Explicit null arguments ("" or '') are retained. Unquoted implicit null arguments, resulting from the expansion of parameters that have no values, are removed. If a parameter with no value is expanded within double quotes, a null argument results and is retained.Expansion and word splittingIf no expansion occurs, no splitting is performed.
@@ -913,7 +907,6 @@ leading 0x or 0X denotes hexadecimal. Otherwise,
When a pattern is used for file name generation, the character . at the start of a file name or immediately following a slash must be matched explicitly, unless the shell option is set. When matching a file name, the slash character must always be matched explicitly. In other cases, the . character is not treated specially.The GLOBIGNORE shell variable may be used to restrict the set of file names matching a pattern. If GLOBIGNORE is set, each matching file name that also matches one of the patterns in GLOBIGNORE is removed from the list of matches. The file names . and .. are always ignored, even when GLOBIGNORE is set. However, setting GLOBIGNORE has the effect of enabling the shell option, so all other file names beginning with a . will match. To get the old behavior of ignoring file names beginning with a ., make .* one of the patterns in GLOBIGNORE. The option is disabled when GLOBIGNORE is unset.
-
Aliases
@@ -946,8 +939,8 @@ alias ping='ping -vc1'
alias sb='ssh blubber'
alias sl='ls'
alias ss='ssh octarine'
-alias sss='ssh -C server1.us.xalasys.com'
-alias sssu='ssh -C -l root server1.us.xalasys.com'
+alias sss='ssh -C server1.us.soti.org'
+alias sssu='ssh -C -l root server1.us.soti.org'
alias tar='gtar'
alias tmp='cd /tmp'
alias unaliasall='unalias -a'
@@ -991,7 +984,6 @@ bash: dh: command not found
Functions are fasterAliases are looked up after functions and thus resolving is slower. While aliases are easier to understand, shell functions are preferred over aliases for almost every purpose.
-
More Bash optionsDisplaying options
@@ -1068,7 +1060,6 @@ bash: VAR: unbound variable
-rw-rw-r-- 1 willy willy 0 Feb 27 13:37 *
-
@@ -1078,7 +1069,6 @@ bash: VAR: unbound variable
Except for the reserved Bourne shell, Bash and special parameters, variable names can be chosen more or less freely.Because a lot of characters have double or even triple meanings, depending on the environment, Bash uses a system of quoting to take away special meaning from one or multiple characters when special treatment is not wanted.Bash uses various methods of expanding command line entries in order to determine which commands to execute.
-
ExercisesFor this exercise, you will need to read the useradd man pages, because we are going to use the /etc/skel directory to hold default shell configuration files, which are copied to the home directory of each newly added user.
@@ -1096,6 +1086,5 @@ bash: VAR: unbound variable
Write a script in which you assign two integer values to two variables. The script should calculate the surface of a rectangle which has these proportions. It should be aired with comments and generate elegant output.Don't forget to chmod your scripts!
-
diff --git a/LDP/guide/docbook/Bash-Beginners-Guide/chap4.xml b/LDP/guide/docbook/Bash-Beginners-Guide/chap4.xml
index 2942cb81..a164ad9f 100644
--- a/LDP/guide/docbook/Bash-Beginners-Guide/chap4.xml
+++ b/LDP/guide/docbook/Bash-Beginners-Guide/chap4.xml
@@ -178,7 +178,6 @@ for i in /etc/profile.d/*.sh ; do
-
Pattern matching using Bash featuresCharacter ranges
@@ -224,7 +223,6 @@ drwxrwxr-x 4 cathy cathy 4096 Jul 11 2002 OpenOffice.org1.0/
Regular expressions are powerful tools for selecting particular lines from files or output. A lot of UNIX commands use regular expressions: vim, perl, the PostgreSQL database and so on. They can be made available in any language or application using external libraries, and they even found their way to non-UNIX systems. For instance, regular expressions are used in the Excell spreadsheet that comes with the MicroSoft Windows Office suite. In this chapter we got the feel of the grep command, which is indispensable in any UNIX environment.The grep command can do much more than the few tasks we discussed here; we only used it as an example for regular expressions. The GNU grep version comes with plenty of documentation, which you are strongly advised to read!Bash has built-in features for matching patterns and can recognize character classes and ranges.
-
ExercisesThese exercises will help you master regular expressions.
@@ -243,7 +241,6 @@ drwxrwxr-x 4 cathy cathy 4096 Jul 11 2002 OpenOffice.org1.0/
Make a script that checks whether a user exists in /etc/passwd. For now, you can specify the user name in the script, you don't have to work with arguments and conditionals at this stage.Display configuration files in /etc that contain numbers in their names.
-
diff --git a/LDP/guide/docbook/Bash-Beginners-Guide/chap5.xml b/LDP/guide/docbook/Bash-Beginners-Guide/chap5.xml
index 2395039c..91c5779a 100644
--- a/LDP/guide/docbook/Bash-Beginners-Guide/chap5.xml
+++ b/LDP/guide/docbook/Bash-Beginners-Guide/chap5.xml
@@ -222,7 +222,6 @@ This is the final line.
grep sed*
-
Non-interactive editingReading sed commands from a file
@@ -297,12 +296,10 @@ line3
Easy sedAdvanced editors, supporting syntax highlighting, can recognize sed syntax. This can be a great help if you tend to forget backslashes and such.
-
SummaryThe sed stream editor is a powerful command line tool, which can handle streams of data: it can take input lines from a pipe. This makes it fit for non-interactive use. The sed editor uses vi-like commands and accepts regular expressions.The sed tool can read commands from the command line or from a script. It is often used to perform find-and-replace actions on lines containing a pattern.
-
ExercisesThese exercises are meant to further demonstrate what sed can do.
@@ -316,6 +313,5 @@ line3
A long listing of the root directory, /, is used for input. Create a file holding sed commands that check for symbolic links and plain files. If a file is a symbolic link, precede it with a line like --This is a symlink--. If the file is a plain file, add a string on the same line, adding a comment like <--- this is a plain file.Create a script that shows lines containing trailing white spaces from a file. This script should use a sed script and show sensible information to the user.
-
diff --git a/LDP/guide/docbook/Bash-Beginners-Guide/chap6.xml b/LDP/guide/docbook/Bash-Beginners-Guide/chap6.xml
index 537c3e79..78ae90dd 100644
--- a/LDP/guide/docbook/Bash-Beginners-Guide/chap6.xml
+++ b/LDP/guide/docbook/Bash-Beginners-Guide/chap6.xml
@@ -45,14 +45,11 @@ contain function definitions, loops, conditions and other programming constructs
-
-Fields as interpreted by awk: first column is $1, second column is $2 and so on.
-In the output of ls , there are 9 columns. The print statement uses these fields as follows:
-kelly@octarine ~/test>ls | awk '{ print $9 $5 }'
+kelly@octarine ~/test>ls | awk '{ print $5 $9 }'
160orig
121script.sed
120temp_file
@@ -125,9 +122,9 @@ Partition /home : 70% full!
Slashes need to be escaped, because they have a special meaning to the awk program.
-Below another example where we search the /etc directory for files ending in .conf and starting with either aorx, using extended regular expressions:
+Below another example where we search the /etc directory for files ending in .conf and starting with either a or x:
-kelly is in /etc>ls | awk '/\<(a|x).*\.conf$/ { print $9 }'
+kelly is in /etc>ls | awk '/\<[a|x].*\.conf$/ { print $9 }'
amd.conf
antivir.conf
xcdroast.conf
@@ -187,7 +184,6 @@ Partition /usr : 97% full!
Syntax highlightingAwk is a programming language. Its syntax is recognized by most editors that can do syntax highlighting for other languages, such as C, Bash, HTML, etc.
-
Gawk variablesAs awk is processing the input file, it uses several variables. Some are editable, some are read-only.
@@ -318,7 +314,7 @@ Total revenue: 19500
kelly@octarine ~/html>cat make-html-from-text.awk
BEGIN { print "<html>\n<head><title>Awk-generated HTML</title></head>\n<body bgcolor=\"#ffffff\">\n<pre>" }
{ print $0 }
-END { print "</pre>\n</body>\n</html>" }
+END { print "</pre>\n</body>\n</html<" }
And the command to execute is also much more straightforward when using awk instead of sed:
@@ -339,7 +335,6 @@ END { print "</pre>\n</body>\n</html>" }
The gawk utility interprets a special-purpose programming language, handling simple data-reformatting jobs with just a few lines of code. It is the free version of the general UNIX awk command.This tools reads lines of input data and can easily recognize columned output. The print program is the most common for filtering and formatting defined fields.On-the-fly variable declaration is straightforward and allows for simple calculation of sums, statistics and other operations on the processed input stream. Variables and commands can be put in awk scripts for background processing.
-
Exercises
diff --git a/LDP/guide/docbook/Bash-Beginners-Guide/chap7.xml b/LDP/guide/docbook/Bash-Beginners-Guide/chap7.xml
index b72379bc..9094d68f 100644
--- a/LDP/guide/docbook/Bash-Beginners-Guide/chap7.xml
+++ b/LDP/guide/docbook/Bash-Beginners-Guide/chap7.xml
@@ -175,7 +175,7 @@ not a local account
anny >echo $num
201
-anny >if [ "num" > 150 ]
+anny >if [ "num" > "150" ]More input>then echo ; echo "you've worked hard enough for today."More input>echo ; fi
@@ -211,9 +211,15 @@ fi
With Bash, you can shorten this type of construct. The compact equivalent of the above test is as follows:
-[ "$(whoami)" != 'root' ] && echo you are using a non-privileged account
+[ "$(whoami)" != 'root' ] && ( echo you are using a non-privileged account; exit 1 )
-Regular expressions may also be used:
+Real Programmers
+Most programmers will even prefer to use test, which is equivalent to using the square brackets, like this:
+
+test "$(whoami)" != 'root' && ( echo you are using a non-privileged account; exit 1)
+
+
+Regular expressions may also be used in comparisons:anny >gender="female"
@@ -268,9 +274,6 @@ your account is managed from the local /etc/passwd file
-
-Simple if/then/else/fi construct: if [ "$1" == fish ]; then echo "Tux likes this"; else echo "Tux wants fish!"; fi
-Here's another example, using two arguments:
@@ -364,7 +367,7 @@ fi
CONSEQUENT-COMMANDS;elif MORE-TEST-COMMANDS; thenMORE-CONSEQUENT-COMMANDS;
-else ALTERNATE-CONSEQUENT-COMMANDS;
+else ALTERNATE-CONSEQUENT-COMMANDS; thenfiThe TEST-COMMANDS list is executed, and if its return status is zero, the CONSEQUENT-COMMANDS list is executed. If
TEST-COMMANDS returns a non-zero status, each elif list is executed in turn, and if its exit status is zero, the corresponding MORE-CONSEQUENT-COMMANDS is executed and the command completes. If else is followed by an ALTERNATE-CONSEQUENT-COMMANDS list, and the final command in the final if or elif clause has a non-zero exit status, then ALTERNATE-CONSEQUENT-COMMANDS is executed. The return status is the exit status of the last command executed, or zero if no condition tested true.
@@ -390,7 +393,7 @@ fi
Nested if statements
-Inside the if statement, you can use another if statement. You may use as many levels of nested ifs as you can logically manage.
+Inside the if statement, you can use another if statement. You may virtually use as many levels of nested ifs as you can logically manage (actually the number of nested ifs is limited to 2500, but it is dubious that anybody would ever need that many).This is an example testing leap years:anny ~/testdir>cat testleap.sh
@@ -427,9 +430,6 @@ This is not a leap year.
-
-year=`date +%Y`; if (( ("$year" % 400) == "0" )) || (( ("$year" % 4 == "0") && ("$year" % 100 != "0") )); then echo "this is a leap year."; else echo "not a leap year"; fi
-We use the double brackets for testing an arithmetic expression, see . This is equivalent to the let statement. You will get stuck using angular brackets here, if you try something like $[$year % 400], because here, the angular brackets don't represent an actual command by themselves.
@@ -609,7 +609,6 @@ esac
In this chapter we learned how to build conditions into our scripts so that different actions can be undertaken upon success or failure of a command. The actions can be determined using the if statement. This allows you to perform arithmetic and string comparisons, and testing of exit code, input and files needed by the script.A simple if/then/fi test often preceeds commands in a shell script in order to prevent output generation, so that the script can easily be run in the background or through the cron facility. More complex definitions of conditions are usually put in a case statement.Upon successful condition testing, the script can explicitly inform the parent using the exit 0 status. Upon failure, any other number may be returned. Based on the return code, the parent program can take appropriate action.
-
ExercisesHere are some ideas to get you started using if in scripts:
@@ -625,6 +624,5 @@ esac
The script should also check for available diskspace. Keep in mind that at any given moment you could have the data in your home directory, the data in the .tar file and the data in the compressed archive all together on your disk. If there is not enough diskspace, exit with an error message in the log file.The script should clean up the compressed archive before it exits.
-
diff --git a/LDP/guide/docbook/Bash-Beginners-Guide/chap8.xml b/LDP/guide/docbook/Bash-Beginners-Guide/chap8.xml
index fcb74f04..b428c142 100644
--- a/LDP/guide/docbook/Bash-Beginners-Guide/chap8.xml
+++ b/LDP/guide/docbook/Bash-Beginners-Guide/chap8.xml
@@ -152,7 +152,6 @@ Usage of the feed script: ./feed.sh food-on-menu animal-name
For more information about the printf command and the way it allows you to format output, see the Bash info pages.
-
Catching user inputUsing the read built-in command
@@ -570,12 +569,10 @@ Transaction(s) Complete
-
SummaryIn this chapter, we learned how to provide user comments and how to prompt for user input. This is usually done using the echo/read combination. We also discussed how files can be used as input and output using file descriptors and redirection, and how this can be combined with getting input from the user.We stressed the importance of providing ample message for the users of our scripts. As always when others use your scripts, it is better to give too much information than not enough. Here documents is a type of shell construct that allows creation of lists, holding choices for the users. This construct can also be used to execute otherwise interactive tasks in the background, without intervention.
-
ExercisesThese exercises are practical applications of the constructs discussed in this chapter. When writing the scripts, you may test by using a test directory that does not contain too much data. Write each step, then test that portion of code, rather than writing everything at once.
@@ -593,7 +590,7 @@ Transaction(s) Complete
Compress the backup using any compression tool. Inform the user that the script is doing this, because it might take some time, during which the user might start worrying if no output appears on the screen.Print a message informing the user about the size of the compressed backup.
-See info tar or Introduction to Linux, chapter 9: Preparing your data for background information.
+See info tar or Introduction to Linux, chapter 9: Preparing your data for background information.Write a script called simple-useradd.sh that adds a local user to the system. This script should:
@@ -607,6 +604,5 @@ Transaction(s) Complete
Rewrite the script from so that it reads input from the user instead of taking it from the first argument.
-
diff --git a/LDP/guide/docbook/Bash-Beginners-Guide/chap9.xml b/LDP/guide/docbook/Bash-Beginners-Guide/chap9.xml
index 364520fc..3a5f480d 100644
--- a/LDP/guide/docbook/Bash-Beginners-Guide/chap9.xml
+++ b/LDP/guide/docbook/Bash-Beginners-Guide/chap9.xml
@@ -55,7 +55,6 @@ done
Since we don't do a line count here, there is no way of knowing the line number from which to start deleting lines until reaching the end. The problem is solved using tac, which reverses the lines in a file.
-
The while loopWhat is it?
@@ -84,31 +83,14 @@ done
Nested while loopsThe example below was written to copy pictures that are made with a webcam to a web directory. Every five minutes a picture is taken. Every hour, a new directory is created, holding the images for that hour. Every day, a new directory is created containing 24 subdirectories. The script runs in the background.
-
-#!/bin/bash
-
-# This script copies files from my homedirectory into the webserver directory.
-# (use scp and SSH keys for a remote directory)
-# A new directory is created every hour.
-
-PICSDIR=/home/carol/pics
-WEBDIR=/var/www/carol/webcam
-
-while true; do
- DATE=`date +%Y%m%d`
- HOUR=`date +%H`
- mkdir $WEBDIR/"$DATE"
-
- while [ $HOUR -ne "00" ]; do
- DESTDIR=$WEBDIR/"$DATE"/"$HOUR"
- mkdir "$DESTDIR"
- mv $PICDIR/*.jpg "$DESTDIR"/
- sleep 3600
- HOUR=`date +%H`
- done
-done
-
-
+Nested while loops - picturesort.sh
+
+
+
+
+
+
+Note the use of the true statement. This means: continue execution until we are forcibly interrupted (with kill or Ctrl+C).This small script can be used for simulation testing; it generates files:
@@ -121,10 +103,7 @@ touch pic-`date +%s`.jpg
sleep 300
done
-Note the use of the date command to generate all kinds of file and directory names. See the man page for more.
-Use the system
-The previous example is for the sake of demonstration. Regular checks can easily be achieved using the system's cron facility. Do not forget to redirect output and errors when using scripts that are executed from your crontab!
-
+Note the use of the date command to generate all kinds of file and directory names.Using keyboard input to control the while loopThis script can be interrupted by the user when a Ctrl+C sequence is entered:
@@ -198,7 +177,6 @@ echo "Exiting."
-
The until loopWhat is it?
@@ -210,43 +188,16 @@ echo "Exiting."
ExampleAn improved picturesort.sh script (see ), which tests for available disk space. If not enough disk space is available, remove pictures from the previous months:
-
-#!/bin/bash
-
-# This script copies files from my homedirectory into the webserver directory.
-# A new directory is created every hour.
-# If the pics are taking up too much space, the oldest are removed.
-
-while true; do
- DISKFUL=$(df -h $WEBDIR | grep -v File | awk '{print $5 }' | cut -d "%" -f1 -)
-
- until [ $DISKFUL -ge "90" ]; do
-
- DATE=`date +%Y%m%d`
- HOUR=`date +%H`
- mkdir $WEBDIR/"$DATE"
-
- while [ $HOUR -ne "00" ]; do
- DESTDIR=$WEBDIR/"$DATE"/"$HOUR"
- mkdir "$DESTDIR"
- mv $PICDIR/*.jpg "$DESTDIR"/
- sleep 3600
- HOUR=`date +%H`
- done
-
- DISKFULL=$(df -h $WEBDIR | grep -v File | awk '{ print $5 }' | cut -d "%" -f1 -)
- done
-
- TOREMOVE=$(find $WEBDIR -type d -a -mtime +30)
- for i in $TOREMOVE; do
- rm -rf "$i";
- done
-
-done
-
+More nested while loops - safesort.sh
+
+
+
+
+
+
+Note the initialization of the HOUR and DISKFULL variables and the use of options with ls and date in order to obtain a correct listing for TOREMOVE.
-
I/0 redirection and loopsInput redirection
@@ -279,7 +230,6 @@ done
Files are compressed before they are moved into the archive directory.
-
Break and continueThe break built-in
@@ -419,7 +369,6 @@ new name for TEST is test
The tr is part of the textutils package; it can perform all kinds of character transformations.
-
Making menus with the select built-inGeneral
@@ -488,7 +437,6 @@ rm "$QUIT"
Any statement within a select construct can be another select loop, enabling (a) submenu(s) within a menu.By default, the PS3 variable is not changed when entering a nested select loop. If you want a different prompt in the submenu, be sure to set it at the appropriate time(s).
-
The shift built-inWhat does it do?
@@ -515,6 +463,7 @@ while (( "$#" )); do
if [[ "$(ls $1)" == "" ]]; then
echo "Empty directory, nothing to be done."
+ shift
else
find $1 -type f -a -atime +365 -exec rm -i {} \;
fi
@@ -523,11 +472,6 @@ shift
done
--exec vs. xargs
-The above find command can be replaced with the following:
-find | xargs [commands_to_execute_on_found_files
-The xargs command builds and executes command lines from standard input. This has the advantage that the command line is filled until the system limit is reached. Only then will the command to execute be called, in the above example this would be rm. If there are more arguments, a new command line will be used, until that one is full or until there are no more arguments. The same thing using find calls on the command to execute on the found files every time a file is found. Thus, using xargs greatly speeds up your scripts and the performance of your machine.
-In the next example, we modified the script from so that it accepts multiple packages to install at once:
#!/bin/bash
@@ -543,14 +487,12 @@ while (($#)); do
done
-
SummaryIn this chapter, we discussed how repetitive commands can be incorporated in loop constructs. Most common loops are built using the for, while or until statements, or a combination of these commands. The for loop executes a task a defined number of times. If you don't know how many times a command should execute, use either until or while to specify when the loop should end.Loops can be interrupted or reiterated using the break and continue statements.A file can be used as input for a loop using the input redirection operator, loops can also read output from commands that is fed into the loop using a pipe.The select construct is used for printing menus in interactive scripts. Looping through the command line arguments to a script can be done using the shift statement.
-
ExercisesRemember: when building scripts, work in steps and test each step before incorporating it in your script.
@@ -571,6 +513,5 @@ done
-
diff --git a/LDP/guide/docbook/Bash-Beginners-Guide/gloss.xml b/LDP/guide/docbook/Bash-Beginners-Guide/gloss.xml
index 7d87fcfb..b148036b 100644
--- a/LDP/guide/docbook/Bash-Beginners-Guide/gloss.xml
+++ b/LDP/guide/docbook/Bash-Beginners-Guide/gloss.xml
@@ -1386,13 +1386,6 @@
X
-
- xargs
-
- Build and execute command lines from standard input.
-
-
-
xauth
diff --git a/LDP/guide/docbook/Bash-Beginners-Guide/index-gloss.xml b/LDP/guide/docbook/Bash-Beginners-Guide/index-gloss.xml
index 05e09510..897e91af 100644
--- a/LDP/guide/docbook/Bash-Beginners-Guide/index-gloss.xml
+++ b/LDP/guide/docbook/Bash-Beginners-Guide/index-gloss.xml
@@ -139,7 +139,7 @@
character classes
- ,
+ ,
@@ -255,7 +255,7 @@
else
-
+
@@ -338,7 +338,7 @@
exit
-
+
@@ -380,7 +380,7 @@
file name expansion
-
+
@@ -948,7 +948,7 @@
standard output
-
+