added

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

@@ -0,0 +1,43 @@
+#!/bin/bash
+# assert.sh
+
+assert ()                 #  If condition false,
+{                         #+ exit from script with error message.
+  E_PARAM_ERR=98
+  E_ASSERT_FAILED=99
+
+
+  if [ -z "$2" ]          # Not enough parameters passed.
+  then
+    return $E_PARAM_ERR   # No damage done.
+  fi
+
+  lineno=$2
+
+  if [ ! $1 ] 
+  then
+    echo "Assertion failed:  \"$1\""
+    echo "File $0, line $lineno"
+    exit $E_ASSERT_FAILED
+  # else
+  #   return
+  #   and continue executing script.
+  fi  
+}    
+
+
+a=5
+b=4
+condition="$a -lt $b"     # Error message and exit from script.
+                          #  Try setting "condition" to something else,
+                          #+ and see what happens.
+
+assert "$condition" $LINENO
+# The remainder of the script executes only if the "assert" does not fail.
+
+
+# Some commands.
+# ...
+# Some more commands.
+
+exit 0

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

@@ -0,0 +1,18 @@
+#!/bin/bash
+# bashandperl.sh
+
+echo "Greetings from the Bash part of the script."
+# More Bash commands may follow here.
+
+exit 0
+# End of Bash part of the script.
+
+# =======================================================
+
+#!/usr/bin/perl
+# This part of the script must be invoked with -x option.
+
+print "Greetings from the Perl part of the script.\n";
+# More Perl commands may follow here.
+
+# End of Perl part of the script.

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

@@ -0,0 +1,40 @@
+#!/bin/bash
+# idelete.sh: Deleting a file by its inode number.
+
+#  This is useful when a filename starts with an illegal character,
+#+ such as ? or -.
+
+ARGCOUNT=1                      # Filename arg must be passed to script.
+E_WRONGARGS=70
+E_FILE_NOT_EXIST=71
+E_CHANGED_MIND=72
+
+if [ $# -ne "$ARGCOUNT" ]
+then
+  echo "Usage: `basename $0` filename"
+  exit $E_WRONGARGS
+fi  
+
+if [ ! -e "$1" ]
+then
+  echo "File \""$1"\" does not exist."
+  exit $E_FILE_NOT_EXIST
+fi  
+
+inum=`ls -i | grep "$1" | awk '{print $1}'`
+# inum = inode (index node) number of file
+# Every file has an inode, a record that hold its physical address info.
+
+echo; echo -n "Are you absolutely sure you want to delete \"$1\" (y/n)? "
+read answer
+case "$answer" in
+[nN]) echo "Changed your mind, huh?"
+      exit $E_CHANGED_MIND
+      ;;
+*)    echo "Deleting file \"$1\".";;
+esac
+
+find . -inum $inum -exec rm {} \;
+echo "File "\"$1"\" deleted!"
+
+exit 0

LDP/guide/docbook/abs-guide/int-or-string.sh

@@ -0,0 +1,28 @@
+#!/bin/bash
+# int-or-string.sh
+# Integer or string?
+
+a=2334                   # Integer.
+let "a += 1"
+echo "a = $a "           # Integer, still.
+echo
+
+b=${a/23/BB}             # Transform into a string.
+echo "b = $b"            # BB35
+declare -i b             # Declaring it an integer doesn't help.
+echo "b = $b"            # BB35, still.
+
+let "b += 1"             # BB35 + 1 =
+echo "b = $b"            # 1
+echo
+
+c=BB34
+echo "c = $c"            # BB34
+d=${c/BB/23}             # Transform into an integer.
+echo "d = $d"            # 2334
+let "d += 1"             # 2334 + 1 =
+echo "d = $d"            # 2335
+
+# Variables in Bash are essentially untyped.
+
+exit 0

LDP/guide/docbook/abs-guide/m4.sh

@@ -0,0 +1,14 @@
+#!/bin/bash
+# m4.sh: Using the m4 macro processor
+
+# Strings
+string=abcdA01
+echo "len($string)" | m4                       # 7
+echo "substr($string,4)" | m4                  # A01
+echo "regexp($string,[0-1][0-1],\&Z)" | m4     # 01Z
+
+# Arithmetic
+echo "incr(22)" | m4                           # 23
+echo "eval(99 / 3)" | m4                       # 33
+
+exit 0

LDP/guide/docbook/abs-guide/match-string.sh

@@ -0,0 +1,37 @@
+#!/bin/bash
+# match-string.sh: simple string matching
+
+match_string ()
+{
+  MATCH=0
+  NOMATCH=90
+  PARAMS=2     # Function requires 2 arguments.
+  BAD_PARAMS=91
+
+  [ $# -eq $PARAMS ] || return $BAD_PARAMS
+
+  case "$1" in
+  "$2") return $MATCH;;
+  *   ) return $NOMATCH;;
+  esac
+
+}  
+
+
+a=one
+b=two
+c=three
+d=two
+
+
+match_string $a     # wrong number of parameters
+echo $?             # 91
+
+match_string $a $b  # no match
+echo $?             # 90
+
+match_string $b $d  # match
+echo $?             # 0
+
+
+exit 0		    

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

@@ -0,0 +1,51 @@
+#!/bin/bash
+# ramdisk.sh
+
+#  A "ramdisk" is a segment of system RAM memory
+#+ that 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.
+#
+#  What good 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.
+
+
+E_NON_ROOT_USER=70             # Must run as root.
+ROOTUSER_NAME=root
+
+MOUNTPT=/mnt/ramdisk
+SIZE=2000                      # 2K blocks (change as appropriate)
+BLOCKSIZE=1024                 # 1K (1024 byte) block size
+DEVICE=/dev/ram0               # First ram device
+
+username=`id -nu`
+if [ "$username" != "$ROOTUSER_NAME" ]
+then
+  echo "Must be root to run \"`basename $0`\"."
+  exit $E_NON_ROOT_USER
+fi
+
+if [ ! -d "$MOUNTPT" ]         #  Test whether mount point already there,
+then                           #+ so no error if this script is run
+  mkdir $MOUNTPT               #+ multiple times.
+fi
+
+dd if=/dev/zero of=$DEVICE count=$SIZE bs=$BLOCKSIZE  # Zero out RAM device.
+mke2fs $DEVICE                 # Create an ext2 filesystem on it.
+mount $DEVICE $MOUNTPT         # Mount it.
+chmod 777 $MOUNTPT             # So ordinary user can access ramdisk.
+                               # However, must be root to unmount it.
+
+echo "\"$MOUNTPT\" now available for use."
+# The ramdisk is now accessible for storing files, even by an ordinary user.
+
+#  Caution, the ramdisk is volatile, and its contents will disappear
+#+ on reboot or power loss.
+#  Copy anything you want saved to a regular directory.
+
+# After reboot, run this script again to set up ramdisk.
+# Remounting /mnt/ramdisk without the other steps will not work.
+
+exit 0

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

@@ -0,0 +1,24 @@
+#!/bin/bash
+# recurse.sh
+
+#  Can a script recursively call itself?
+#  Yes, but this is of little or no practical use
+#+ except perhaps as a "proof of concept".
+
+RANGE=10
+MAXVAL=9
+
+i=$RANDOM
+let "i %= $RANGE"  # Generate a random number between 0 and $MAXVAL.
+
+if [ "$i" -lt "$MAXVAL" ]
+then
+  echo "i = $i"
+  ./$0             #  Script recursively spawns a new instance of itself.
+fi                 #  Each child script does the same, until
+                   #+ a generated $i equals $MAXVAL.
+
+#  Using a "while" loop instead of an "if/then" test causes problems.
+#  Exercise for the reader: Explain why.
+
+exit 0

LDP/guide/docbook/abs-guide/redir4a.sh

@@ -0,0 +1,27 @@
+#!/bin/bash
+
+if [ -z "$1" ]
+then
+  Filename=names.data          # Default, if no filename specified.
+else
+  Filename=$1
+fi  
+
+Savefile=$Filename.new         # Filename to save results in.
+FinalName=Jonah                # Name to terminate "read" on.
+
+line_count=`wc $Filename | awk '{ print $1 }'`  # Number of lines in target file.
+
+
+for name in `seq $line_count`
+do
+  read name
+  echo "$name"
+  if [ "$name" = "$FinalName" ]
+  then
+    break
+  fi  
+done < "$Filename" > "$Savefile"     # Redirects stdin to file $Filename,
+#    ^^^^^^^^^^^^^^^^^^^^^^^^^^^       and saves it to backup file.
+
+exit 0

LDP/guide/docbook/abs-guide/symlinks2.sh

@@ -0,0 +1,22 @@
+#!/bin/bash
+# symlinks.sh: Lists symbolic links in a directory.
+
+ARGS=1                 # Expect one command-line argument.
+OUTFILE=symlinks.list  # save file
+
+if [ $# -ne "$ARGS" ]  # If not 1 arg...
+then
+  directory=`pwd`      # current working directory
+else
+  directory=$1
+fi
+
+echo "symbolic links in directory \"$directory\""
+
+for file in $( find $directory -type l )   # -type l = symbolic links
+do
+  echo "$file"
+done | sort > "$OUTFILE"                   # stdout of loop
+#           ^^^^^^^^^^^^                     redirected to save file.
+
+exit 0