updated

LDP/guide/docbook/abs-guide/Change.log

@@ -6,8 +6,96 @@
              http://personal.riverusers.com/~thegrendel/Change.log
 ------------------------------------------------------------------------
 
-Release.
-Version 2.6 'SALAL' release, 03/15/04
+Version 2.7
+Mulberry release, 04/18/04
+
+1) In the "Starting Off With a Sha-Bang" chapter:
+   Added "ex1a.sh" example as a bridge between "ex1.sh" and "ex2.sh"
+   examples.
+   Added a few explanatory notes.
+   Minor revisions to comments in "ex1.sh" and "ex2.sh" examples.
+   Added "$" to variable name in script prolog note.
+   Minor revisions to "Why Shell Programming?" section. 
+
+2) In "Special Characters" chapter:
+   In in-line example at "Control-K" entry, expanded explanation of
+   effect of a vertical tab.
+   (Thank you, Lee Maschmeyer.)
+   Minor rewording at "`" (backticks), "\" (escape), and other entries.
+
+3) In "Quoting" chapter:
+   Slight rewording of note about certain programs expanding special
+   characters in a quoted string.
+   Dropped word "apparently" from footnote on quoting "!" character.
+
+4) In "/dev" section of "/dev and /proc" chapter:
+   Added short explanation of Bash's treatment of /dev/tcp/host/port
+   pseudo-device files.
+   Added footnote defining a socket.
+   Added use of /dev/sda1 in mounting a USB flash drive.
+   Added examples of getting the time from a remote network
+   and downloading a URL -- using /dev/tcp.
+   (Thank you, Mark.)
+
+5) In "/proc" section of "/dev and /proc" chapter:
+   Added "cat /proc/apm" to list of 'proc' examples.
+   Redid first parsing example.
+
+6) In the "Portability Issues" section of the "Miscellany" chapter:    
+   Added discussion of using !#/bin/sh to run scripts.
+   (Thank you, Ian D. Allen.)
+
+7) In "Assorted Tips" section of "Miscellany" chapter:
+   Added redirecting stderr to stdout in "if-grep" test.
+   (Thank you, Chris Martin.)
+   Added tip about setting PATH and umask at beginning of script.
+   (Thank you, Ian D. Allen.)
+
+8) In "System and Administrative Commands" chapter:
+   At "ifconfig" entry, added "ifconfig -a" output example.
+   At "hostname" entry, added note about "domainname" and similar
+   commands.
+   At "netstat" entry, added screen output example.
+
+9) In "Text Processing" section of "External Commands" Chapter:   
+   Added comment (suggested modification) to "wf.sh" example.
+   (Thanks, Arun Giridhar.)
+   At "grep" entry, added method of searching for two different patterns,
+   with usage example.
+
+10) In "Internal Commands and Builtins" chapter:
+    Expanded "ex43.sh" example.
+
+11) In "Comparison Operators" section of "Tests" chapter:
+    Changed section title.
+    Added brief intro paragraph.
+    At "==" entry, added note and embedded pre-existing example within it.
+
+12) In "Regular Expressions" chapter:
+    In "Brief Introduction to Regular Expression" Section:
+      Added sidebar with example of testing an RE.
+    In "Globbing" Section:
+      Fixed typo in footnote 1.
+      (Thanks (Asheesh Soni.)
+
+13) In "Copyright" chapter:
+    Added URL for French translation.
+
+14) In "Contributed Scripts" appendix:
+    Replaced "tree.sh" script with a simplified version,
+    revised by Rick Boivie.
+
+15) Added "To Do List" appendix.
+
+16) Changed all "process id" references to "process ID" to avoid
+    confusion.
+
+17) Minor cleanups and fixups to various scripts.
+
+
+
+Version 2.6
+'SALAL' release, 03/15/04
 
 1) In "Exit and Exit Status" chapter,
    Added comment to inline example discussing negation of a 'true' command.
@@ -172,7 +260,7 @@ Version 2.5
     Noted that GNU tools allow extended REs if escaped.
     Removed brackets from RE character sets where unnecessary and
     misleading.
-    In "Globbing Section":
+    In "Globbing" Section:
     Corrected note about 'echo' performing wildcard expansion.
     (Thanks, Paulo Marcel Coelho Aragao, for all of the above.)
     Broke 'echo' filename expansion examples out of main "screen" block.
@@ -483,7 +571,7 @@ Comments: Major release.
    in the environment (exported).
    (Thank you, Mr. Fred.)
 
-9) In "Comparison Operations" section of "Tests" chapter:
+9) In "Comparison Operators" section of "Tests" chapter:
    Corrected typos in "str-test.sh" example.
    (Thank you, Bill Gradwohl.)
 
@@ -2378,7 +2466,7 @@ In "External Filters, Programs, and Commands" section:
     to Produce This Book".    
 
 89) Added footnote about shell script naming conventions to "Why Shell
-    Programming?" section. 
+    Programming?" section of Chapter 1. 
 
 90) Changed all <errorcode> tags to the more appropriate <returnvalue>.
 

LDP/guide/docbook/abs-guide/Du.sh

@@ -13,7 +13,8 @@ NEWFILENAME=$1.unx
 
 CR='\015'  # Carriage return.
            # 015 is octal ASCII code for CR.
-           # Lines in a DOS text file end in a CR-LF.
+           # Lines in a DOS text file end in CR-LF.
+           # Lines in a UNIX text file end in LF only.
 
 tr -d $CR < $1 > $NEWFILENAME
 # Delete CR's and write to new file.

LDP/guide/docbook/abs-guide/crypto-quote.sh

@@ -1,7 +1,7 @@
 #!/bin/bash
 # crypto-quote.sh: Encrypt quotes
 
-# Will encrypt famous quotes in a simple monoalphabetic substitution.
+#  Will encrypt famous quotes in a simple monoalphabetic substitution.
 #  The result is similar to the "Crypto Quote" puzzles
 #+ seen in the Op Ed pages of the Sunday paper.
 
@@ -20,7 +20,7 @@ cat "$@" | tr "a-z" "A-Z" | tr "A-Z" "$key"
 # Passes non-alphabetic characters through unchanged.
 
 
-# Try this script with something like
+# Try this script with something like:
 # "Nothing so needs reforming as other people's habits."
 # --Mark Twain
 #

LDP/guide/docbook/abs-guide/csubloop.sh

@@ -18,6 +18,7 @@ done`
 
 echo "variable2 = $variable2"  # variable2 = 0123456789
 
-# It's possible to embed a loop within a variable declaration.
+#  Demonstrates that it's possible to embed a loop
+#+ within a variable declaration.
 
 exit 0

LDP/guide/docbook/abs-guide/empty-array.sh

@@ -8,8 +8,8 @@
 # An empty array is not the same as an array with empty elements.
 
 array0=( first second third )
-array1=( '' )   # "array1" has one empty element.
-array2=( )      # No elements... "array2" is empty.
+array1=( '' )   # "array1" consists of one empty element.
+array2=( )      # No elements . . . "array2" is empty.
 
 echo
 ListArray()
@@ -24,7 +24,7 @@ echo "Length of first element in array1 = ${#array1}"
 echo "Length of first element in array2 = ${#array2}"
 echo
 echo "Number of elements in array0 = ${#array0[*]}"  # 3
-echo "Number of elements in array1 = ${#array1[*]}"  # 1  (surprise!)
+echo "Number of elements in array1 = ${#array1[*]}"  # 1  (Surprise!)
 echo "Number of elements in array2 = ${#array2[*]}"  # 0
 }
 
@@ -32,7 +32,7 @@ echo "Number of elements in array2 = ${#array2[*]}"  # 0
 
 ListArray
 
-# Try extending those arrays
+# Try extending those arrays.
 
 # Adding an element to an array.
 array0=( "${array0[@]}" "new1" )
@@ -56,44 +56,44 @@ echo
 echo "Stack height for array2 = $height"
 
 # The 'pop' is:
-unset array2[${#array2[@]}-1]	# Arrays are zero based
-height=${#array2[@]}
+unset array2[${#array2[@]}-1]	#  Arrays are zero-based,
+height=${#array2[@]}            #+ which means first element has index 0.
 echo
 echo "POP"
 echo "New stack height for array2 = $height"
 
 ListArray
 
-# List only 2nd and 3rd elements of array0
-from=1		# Zero based numbering
+# List only 2nd and 3rd elements of array0.
+from=1		# Zero-based numbering.
 to=2		#
 array3=( ${array0[@]:1:2} )
 echo
 echo "Elements in array3:  ${array3[@]}"
 
-# Works like a string (array of characters)
-# Try some other "string" forms
+# Works like a string (array of characters).
+# Try some other "string" forms.
 
-# Replacement
+# Replacement:
 array4=( ${array0[@]/second/2nd} )
 echo
 echo "Elements in array4:  ${array4[@]}"
 
-# Replace all matching wildcarded string
+# Replace all matching wildcarded string.
 array5=( ${array0[@]//new?/old} )
 echo
 echo "Elements in array5:  ${array5[@]}"
 
-# Just when you are getting the feel for this...
+# Just when you are getting the feel for this . . .
 array6=( ${array0[@]#*new} )
-echo # This one might surprise you
+echo # This one might surprise you.
 echo "Elements in array6:  ${array6[@]}"
 
 array7=( ${array0[@]#new1} )
-echo # After array6 this should not be a surprise
+echo # After array6 this should not be a surprise.
 echo "Elements in array7:  ${array7[@]}"
 
-# Which looks a lot like...
+# Which looks a lot like . . .
 array8=( ${array0[@]/new1/} )
 echo
 echo "Elements in array8:  ${array8[@]}"
@@ -102,9 +102,9 @@ echo "Elements in array8:  ${array8[@]}"
 
 #  The string operations are performed on
 #+ each of the elements in var[@] in succession.
-#  Therefore : BASH supports string vector operations
-#  If the result is a zero length string, that
-#+ element disappears in the resulting assignment.
+#  Therefore : Bash supports string vector operations
+#+ if the result is a zero length string,
+#+ that element disappears in the resulting assignment.
 
 #  Question, are those strings hard or soft quotes?
 
@@ -118,8 +118,8 @@ array10=( ${array0[@]#$zap} )
 echo
 echo "Elements in array10:  ${array10[@]}"
 
-# Compare array7 with array10
-# Compare array8 with array9
+# Compare array7 with array10.
+# Compare array8 with array9.
 
 # Answer: must be soft quotes.
 

LDP/guide/docbook/abs-guide/ex1.sh

@@ -1,4 +1,4 @@
-# cleanup
+# Cleanup
 # Run as root, of course.
 
 cd /var/log

LDP/guide/docbook/abs-guide/ex14.sh

@@ -39,5 +39,5 @@ zcat $1 | most
 
 
 exit $?   # Script returns exit status of pipe.
-# Actually "exit $?" unnecessary, as the script will, in any case,
+# Actually "exit $?" is unnecessary, as the script will, in any case,
 # return the exit status of the last command executed.

LDP/guide/docbook/abs-guide/ex17.sh

@@ -42,7 +42,7 @@ echo "All the command-line parameters are: "$*""
 if [ $# -lt "$MINPARAMS" ]
 then
   echo
-  echo "Give me at least $MINPARAMS command-line arguments!"
+  echo "This script needs at least $MINPARAMS command-line arguments!"
 fi  
 
 echo

LDP/guide/docbook/abs-guide/ex2.sh

@@ -1,6 +1,14 @@
 #!/bin/bash
-# cleanup, version 2
-# Run as root, of course.
+# Cleanup, version 3
+
+#  Warning:
+#  -------
+#  This script uses quite a number of features that will be explained
+#+ later on.
+#  By the time you've finished the first half of the book,
+#+ there should be nothing mysterious about it.
+
+
 
 LOG_DIR=/var/log
 ROOT_UID=0     # Only users with $UID 0 have root privileges.
@@ -9,6 +17,7 @@ E_XCD=66       # Can't change directory?
 E_NOTROOT=67   # Non-root exit error.
 
 
+# Run as root, of course.
 if [ "$UID" -ne "$ROOT_UID" ]
 then
   echo "Must be root to run this script."

LDP/guide/docbook/abs-guide/ex22.sh

@@ -1,14 +1,15 @@
 #!/bin/bash
-# List the planets.
+# Listing the planets.
 
 for planet in Mercury Venus Earth Mars Jupiter Saturn Uranus Neptune Pluto
 do
-  echo $planet
+  echo $planet  # Each planet on a separate line.
 done
 
 echo
 
 for planet in "Mercury Venus Earth Mars Jupiter Saturn Uranus Neptune Pluto"
+# All planets on same line.
 # Entire 'list' enclosed in quotes creates a single variable.
 do
   echo $planet

LDP/guide/docbook/abs-guide/ex42.sh

@@ -19,12 +19,12 @@ ls . | xargs -i -t cp ./{} $1
 #  {} is a placeholder for output text.
 #  This is similar to the use of a curly bracket pair in "find."
 #
-#  List the files (ls),
+#  List the files in current directory (ls .),
 #+ pass the output of "ls" as arguments to "xargs" (-i -t options),
 #+ then copy (cp) these arguments ({}) to new directory ($1).  
 #
 #  The net result is the exact equivalent of
 #+   cp * $1
-#+ unless any of the filenames has "whitespace" characters.
+#+ unless any of the filenames has embedded "whitespace" characters.
 
 exit 0

LDP/guide/docbook/abs-guide/ex43.sh

@@ -13,4 +13,33 @@ echo $y         #+ but linefeeds removed.
 #  When LF's not preserved, it may make it easier to parse output,
 #+ using utilities such as "awk".
 
+echo
+echo "==========================================================="
+echo
+
+# Now, showing how to "expand" a variable using "eval" . . .
+
+for i in 1 2 3 4 5; do
+  eval value=$i
+  #  value=$i has same effect. The "eval" is not necessary here.
+  #  A variable lacking a meta-meaning evaluates to itself --
+  #+ it can't expand to anything other than its literal self.
+  echo $value
+done
+
+echo
+echo "---"
+echo
+
+for i in ls df; do
+  value=eval $i
+  #  value=$i has an entirely different effect here.
+  #  The "eval" evaluates the commands "ls" and "df" . . .
+  #  The terms "ls" and "df" have a meta-meaning,
+  #+ since they are interpreted as commands,
+  #+ rather than just character strings.
+  echo $value
+done
+
+
 exit 0

LDP/guide/docbook/abs-guide/ex44.sh

@@ -11,7 +11,7 @@ $killppp                  # This variable is now a command.
 
 # The following operations must be done as root user.
 
-chmod 666 /dev/ttyS3      # Must be read+write permissions, or else?
+chmod 666 /dev/ttyS3      # Must be read+write permissions, or else what?
 #  Since doing a SIGKILL on ppp changed the permissions on the serial port,
 #+ we restore permissions to previous state.
 

LDP/guide/docbook/abs-guide/ex6.sh

@@ -1,6 +1,7 @@
 #!/bin/bash
 
-# Check some of the system's environmental variables.
+#  Check some of the system's environmental variables.
+#  This is good preventative maintenance.
 #  If, for example, $USER, the name of the person at the console, is not set,
 #+ the machine will not recognize you.
 
@@ -43,9 +44,12 @@ echo
 #
 #                      echo ${ZZXy23AB?} >/dev/null
 
+#  Compare these methods of checking whether a variable has been set
+#+ with "set -u" . . .
 
 
-echo "You will not see this message, because script terminated above."
+
+echo "You will not see this message, because script already terminated."
 
 HERE=0
-exit $HERE   # Will *not* exit here.
+exit $HERE   # Will NOT exit here.

LDP/guide/docbook/abs-guide/ex70.sh

@@ -4,7 +4,7 @@ wall <<zzz23EndOfMessagezzz23
 E-mail your noontime orders for pizza to the system administrator.
     (Add an extra dollar for anchovy or mushroom topping.)
 # Additional message text goes here.
-# Note: Comment lines printed by 'wall'.
+# Note: 'wall' prints comment lines.
 zzz23EndOfMessagezzz23
 
 # Could have been done more efficiently by

LDP/guide/docbook/abs-guide/ex75.sh

@@ -8,6 +8,7 @@
 
 badname=`ls | grep ' '`
 
+# Try this:
 # echo "$badname"
 
 rm "$badname"

LDP/guide/docbook/abs-guide/online.sh

@@ -4,49 +4,51 @@
 
 TRUE=1
 LOGFILE=/var/log/messages
-# Note that $LOGFILE must be readable (chmod 644 /var/log/messages).
+#  Note that $LOGFILE must be readable
+#+ (as root, chmod 644 /var/log/messages).
 TEMPFILE=temp.$$
-# Create a "unique" temp file name, using process id of the script.
+#  Create a "unique" temp file name, using process id of the script.
 KEYWORD=address
-# At logon, the line "remote IP address xxx.xxx.xxx.xxx"
-#                     appended to /var/log/messages.
+#  At logon, the line "remote IP address xxx.xxx.xxx.xxx"
+#                      appended to /var/log/messages.
 ONLINE=22
 USER_INTERRUPT=13
 CHECK_LINES=100
-# How many lines in log file to check.
+#  How many lines in log file to check.
 
 trap 'rm -f $TEMPFILE; exit $USER_INTERRUPT' TERM INT
-# Cleans up the temp file if script interrupted by control-c.
+#  Cleans up the temp file if script interrupted by control-c.
 
 echo
 
 while [ $TRUE ]  #Endless loop.
 do
   tail -$CHECK_LINES $LOGFILE> $TEMPFILE
-  # Saves last 100 lines of system log file as temp file.
-  # Necessary, since newer kernels generate many log messages at log on.
+  #  Saves last 100 lines of system log file as temp file.
+  #  Necessary, since newer kernels generate many log messages at log on.
   search=`grep $KEYWORD $TEMPFILE`
-  # Checks for presence of the "IP address" phrase,
-  # indicating a successful logon.
+  #  Checks for presence of the "IP address" phrase,
+  #+ indicating a successful logon.
 
-  if [ ! -z "$search" ] # Quotes necessary because of possible spaces.
+  if [ ! -z "$search" ] #  Quotes necessary because of possible spaces.
   then
      echo "On-line"
-     rm -f $TEMPFILE    # Clean up temp file.
+     rm -f $TEMPFILE    #  Clean up temp file.
      exit $ONLINE
   else
-     echo -n "."        # -n option to echo suppresses newline,
-                        # so you get continuous rows of dots.
+     echo -n "."        #  The -n option to echo suppresses newline,
+                        #+ so you get continuous rows of dots.
   fi
 
   sleep 1  
 done  
 
 
-# Note: if you change the KEYWORD variable to "Exit",
-# this script can be used while on-line to check for an unexpected logoff.
+#  Note: if you change the KEYWORD variable to "Exit",
+#+ this script can be used while on-line
+#+ to check for an unexpected logoff.
 
-# Exercise: Change the script, as per the above note,
+# Exercise: Change the script, per the above note,
 #           and prettify it.
 
 exit 0
@@ -61,7 +63,7 @@ while true
 done
 
 # Problem: Hitting Control-C to terminate this process may be insufficient.
-#          (Dots may keep on echoing.)
+#+         (Dots may keep on echoing.)
 # Exercise: Fix this.
 
 
@@ -76,5 +78,5 @@ do echo -n .
 done
 echo "On-line"
 
-# Exercise: Discuss the strengths and weaknesses
-#           of each of these various approaches.
+# Exercise: Discuss the relative strengths and weaknesses
+#!          of each of these various approaches.

LDP/guide/docbook/abs-guide/param-sub.sh

@@ -1,4 +1,9 @@
 #!/bin/bash
+# param-sub.sh
+
+#  Whether a variable has been declared
+#+ affects triggering of the default option
+#+ even if the variable is null.
 
 username0=
 # username0 has been declared, but is set to null.
@@ -13,5 +18,6 @@ username2=
 # username2 has been declared, but is set to null.
 echo "username2 = ${username2:-`whoami`}"
 # Will echo because of :- rather than just - in condition test.
+# Compare to first instance, above.
 
 exit 0

LDP/guide/docbook/abs-guide/pb.sh

@@ -4,11 +4,12 @@
 # Written by Rick Boivie, and used with permission.
 # Modifications by document author.
 
-MINARGS=1     # Script needs at least one argument.
+MINARGS=1     #  Script needs at least one argument.
 DATAFILE=./phonebook
-              # A data file named "phonebook" must exist.
+              #  A data file in current working directory
+              #+ named "phonebook" must exist.
 PROGNAME=$0
-E_NOARGS=70   # No arguments error.
+E_NOARGS=70   #  No arguments error.
 
 if [ $# -lt $MINARGS ]; then
       echo "Usage: "$PROGNAME" data"
@@ -25,11 +26,11 @@ else
 fi
 
 exit 0        #  Script exits here.
-              #  It's o.k. to put non-hashmarked comments
-              #+ and data after this point.
+              #  Therefore, it's o.k. to put
+	      #+ non-hashmarked comments and data after this point.
 
 # ------------------------------------------------------------------------
-# Sample "phonebook" datafile:
+Sample "phonebook" datafile:
 
 John Doe        1555 Main St., Baltimore, MD 21228          (410) 222-3333
 Mary Moe        9899 Jones Blvd., Warren, NH 03787          (603) 898-3232
@@ -45,5 +46,5 @@ Sam Roe         956 E. 8th St., New York, NY 10009          (212) 444-5678
 $bash pb.sh Roe Sam
 Sam Roe         956 E. 8th St., New York, NY 10009          (212) 444-5678
 
-#  When more than one argument passed to script,
+#  When more than one argument is passed to this script,
 #+ it prints *only* the line(s) containing all the arguments.

LDP/guide/docbook/abs-guide/poem.sh

@@ -28,3 +28,7 @@ done
 echo
 
 exit 0
+
+# Exercise:
+# --------
+# Modify this script to pretty-print a poem from a text data file.

LDP/guide/docbook/abs-guide/pw.sh

@@ -1,15 +1,16 @@
 #!/bin/bash
 # May need to be invoked with  #!/bin/bash2  on older machines.
 #
-# Random password generator for bash 2.x by Antek Sawicki <tenox@tenox.tc>,
+# Random password generator for Bash 2.x by Antek Sawicki <tenox@tenox.tc>,
 # who generously gave permission to the document author to use it here.
 #
 # ==> Comments added by document author ==>
 
 
 MATRIX="0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz"
+# ==> Password will consist of alphanumeric characters.
 LENGTH="8"
-# ==> May change 'LENGTH' for longer password, of course.
+# ==> May change 'LENGTH' for longer password.
 
 
 while [ "${n:=1}" -le "$LENGTH" ]
@@ -23,17 +24,17 @@ do
 	# ==> ${#MATRIX} returns length of array MATRIX.
 
 	# ==> $RANDOM%${#MATRIX} returns random number between 1
-	# ==> and length of MATRIX - 1.
+	# ==> and [length of MATRIX] - 1.
 
 	# ==> ${MATRIX:$(($RANDOM%${#MATRIX})):1}
 	# ==> returns expansion of MATRIX at random position, by length 1. 
-	# ==> See {var:pos:len} parameter substitution in Section 3.3.1
-	# ==> and following examples.
+	# ==> See {var:pos:len} parameter substitution in Chapter 9.
+	# ==> and the associated examples.
 
 	# ==> PASS=... simply pastes this result onto previous PASS (concatenation).
 
 	# ==> To visualize this more clearly, uncomment the following line
-	# ==>             echo "$PASS"
+	#                 echo "$PASS"
 	# ==> to see PASS being built up,
 	# ==> one character at a time, each iteration of the loop.
 
@@ -41,6 +42,6 @@ do
 	# ==> Increment 'n' for next pass.
 done
 
-echo "$PASS"      # ==> Or, redirect to file, as desired.
+echo "$PASS"      # ==> Or, redirect to a file, as desired.
 
 exit 0

LDP/guide/docbook/abs-guide/ramdisk.sh

@@ -2,13 +2,13 @@
 # ramdisk.sh
 
 #  A "ramdisk" is a segment of system RAM memory
-#+ that acts as if it were a filesystem.
+#+ which acts as if it were a filesystem.
 #  Its advantage is very fast access (read/write time).
 #  Disadvantages: volatility, loss of data on reboot or powerdown.
-#                 less RAM available to system.
+#+                less RAM available to system.
 #
-#  What good is a ramdisk?
-#  Keeping a large dataset, such as a table or dictionary on ramdisk
+#  Of what use is a ramdisk?
+#  Keeping a large dataset, such as a table or dictionary on ramdisk,
 #+ speeds up data lookup, since memory access is much faster than disk access.
 
 
@@ -33,9 +33,10 @@ then                           #+ so no error if this script is run
 fi
 
 dd if=/dev/zero of=$DEVICE count=$SIZE bs=$BLOCKSIZE  # Zero out RAM device.
+                                                      # Why is this necessary?
 mke2fs $DEVICE                 # Create an ext2 filesystem on it.
 mount $DEVICE $MOUNTPT         # Mount it.
-chmod 777 $MOUNTPT             # So ordinary user can access ramdisk.
+chmod 777 $MOUNTPT             # Enables ordinary user to access ramdisk.
                                # However, must be root to unmount it.
 
 echo "\"$MOUNTPT\" now available for use."
@@ -45,7 +46,11 @@ echo "\"$MOUNTPT\" now available for use."
 #+ on reboot or power loss.
 #  Copy anything you want saved to a regular directory.
 
-# After reboot, run this script again to set up ramdisk.
+# After reboot, run this script to again set up ramdisk.
 # Remounting /mnt/ramdisk without the other steps will not work.
 
+#  Suitably modified, this script can by invoked in /etc/rc.d/rc.local,
+#+ to set up ramdisk automatically at bootup.
+#  That may be appropriate on, for example, a database server.
+
 exit 0

LDP/guide/docbook/abs-guide/random-test.sh

@@ -56,9 +56,13 @@ print_result
 #  Keep in mind that RANDOM is a pseudorandom generator,
 #+ and not a spectacularly good one at that.
 
+#  Randomness is a deep and complex subject.
+#  Sufficiently long "random" sequences may exhibit
+#+ chaotic and other "non-random" behavior.
+
 # Exercise (easy):
 # ---------------
 # Rewrite this script to flip a coin 1000 times.
-# Choices are "HEADS" or "TAILS".
+# Choices are "HEADS" and "TAILS".
 
 exit 0

LDP/guide/docbook/abs-guide/read-novar.sh

@@ -1,4 +1,5 @@
 #!/bin/bash
+# read-novar.sh
 
 echo
 

LDP/guide/docbook/abs-guide/tree.sh

@@ -1,74 +1,59 @@
-#!/bin/sh
-#         @(#) tree      1.1  30/11/95       by Jordi Sanfeliu
-#                                         email: mikaku@fiwix.org
-#
-#         Initial version:  1.0  30/11/95
-#         Next version   :  1.1  24/02/97   Now, with symbolic links
-#         Patch by       :  Ian Kjos, to support unsearchable dirs
-#                           email: beth13@mail.utexas.edu
-#
-#         Tree is a tool for view the directory tree (obvious :-) )
-#
+#!/bin/bash
+# tree.sh
+
+#  Written by Rick Boivie.
+#  Used with permission.
+#  This is a revised and simplified version of a script
+#  by Jordi Sanfeliu (and patched by Ian Kjos).
+#  This script replaces the earlier version used in
+#+ previous releases of the Advanced Bash Scripting Guide.
 
-# ==> 'Tree' script used here with the permission of its author, Jordi Sanfeliu.
 # ==> Comments added by the author of this document.
-# ==> Argument quoting added.
 
 
 search () {
-   for dir in `echo *`
-   # ==> `echo *` lists all the files in current working directory, without line breaks.
-   # ==> Similar effect to     for dir in *
-   # ==> but "dir in `echo *`" will not handle filenames with blanks.
-   do
-      if [ -d "$dir" ] ; then   # ==> If it is a directory (-d)...
-         zz=0                   # ==> Temp variable, keeping track of directory level.
-         while [ $zz != $deep ]    # Keep track of inner nested loop.
-         do
-            echo -n "|   "    # ==> Display vertical connector symbol,
-                              # ==> with 2 spaces & no line feed in order to indent.
-            zz=`expr $zz + 1` # ==> Increment zz.
-         done
-         if [ -L "$dir" ] ; then   # ==> If directory is a symbolic link...
-            echo "+---$dir" `ls -l $dir | sed 's/^.*'$dir' //'`
-	    # ==> Display horiz. connector and list directory name, but...
-	    # ==> delete date/time part of long listing.
-         else
-            echo "+---$dir"      # ==> Display horizontal connector symbol...
-                                 # ==> and print directory name.
-            if cd "$dir" ; then  # ==> If can move to subdirectory...
-               deep=`expr $deep + 1`   # ==> Increment depth.
-               search     # with recursivity ;-)
-                          # ==> Function calls itself.
-               numdirs=`expr $numdirs + 1`   # ==> Increment directory count.
-            fi
-         fi
+for dir in `echo *`
+#  ==> `echo *` lists all the files in current working directory,
+#+ ==> without line breaks.
+#  ==> Similar effect to for dir in *
+#  ==> but "dir in `echo *`" will not handle filenames with blanks.
+do
+  if [ -d "$dir" ] ; then # ==> If it is a directory (-d)...
+  zz=0                    # ==> Temp variable, keeping track of directory level.
+  while [ $zz != $1 ]     # Keep track of inner nested loop.
+    do
+      echo -n "| "        # ==> Display vertical connector symbol,
+                          # ==> with 2 spaces & no line feed in order to indent.
+      zz=`expr $zz + 1`   # ==> Increment zz.
+    done
+
+    if [ -L "$dir" ] ; then # ==> If directory is a symbolic link...
+      echo "+---$dir" `ls -l $dir | sed 's/^.*'$dir' //'`
+      # ==> Display horiz. connector and list directory name, but...
+      # ==> delete date/time part of long listing.
+    else
+      echo "+---$dir"       # ==> Display horizontal connector symbol...
+      # ==> and print directory name.
+      numdirs=`expr $numdirs + 1` # ==> Increment directory count.
+      if cd "$dir" ; then # ==> If can move to subdirectory...
+        search `expr $1 + 1` # with recursion ;-)
+        # ==> Function calls itself.
+        cd ..
       fi
-   done
-   cd ..   # ==> Up one directory level.
-   if [ "$deep" ] ; then  # ==> If depth = 0 (returns TRUE)...
-      swfi=1              # ==> set flag showing that search is done.
-   fi
-   deep=`expr $deep - 1`  # ==> Decrement depth.
+    fi
+  fi
+done
 }
 
-# - Main -
-if [ $# = 0 ] ; then
-   cd `pwd`    # ==> No args to script, then use current working directory.
-else
-   cd $1       # ==> Otherwise, move to indicated directory.
+if [ $# != 0 ] ; then
+  cd $1 # move to indicated directory.
+  #else # stay in current directory
 fi
-echo "Initial directory = `pwd`"
-swfi=0      # ==> Search finished flag.
-deep=0      # ==> Depth of listing.
-numdirs=0
-zz=0
 
-while [ "$swfi" != 1 ]   # While flag not set...
-do
-   search   # ==> Call function after initializing variables.
-done
+echo "Initial directory = `pwd`"
+numdirs=0
+
+search 0
 echo "Total directories = $numdirs"
 
 exit 0
-# ==> Challenge: try to figure out exactly how this script works.

LDP/guide/docbook/abs-guide/wf.sh

@@ -33,14 +33,22 @@ sed -e 's/\.//g'  -e 's/\,//g' -e 's/ /\
 #+ change space between words to linefeed,
 #+ then shift characters to lowercase, and
 #+ finally prefix occurrence count and sort numerically.
+
+#  Arun Giridhar suggests modifying the above to:
+#  . . . | sort | uniq -c | sort +1 [-f] | sort +0 -nr
+#  This adds a secondary sort key, so instances of
+#+ equal occurrence are sorted alphabetically.
+#  As he explains it:
+#  "This is effectively a radix sort, first on the
+#+ least significant column
+#+ (word or string, optionally case-insensitive)
+#+ and last on the most significant column (frequency)."
 ########################################################
 
+exit 0
+
 # Exercises:
 # ---------
 # 1) Add 'sed' commands to filter out other punctuation,
 #+   such as semicolons.
 # 2) Modify to also filter out multiple spaces and other whitespace.
-# 3) Add a secondary sort key, so that instances of equal occurrence
-#+   are sorted alphabetically.
-
-exit 0