Easily find issues by searching: #<Issue ID>
Example: #1832
Easily find members by searching in: <username>, <first name> and <last name>.
Example: Search smith, will return results smith and adamsmith
These scripts, while not fitting into the text of this document, do illustrate some interesting shell programming techniques. Some are useful, too. Have fun analyzing and running them.
Example A-1. mailformat: Formatting an e-mail message
#!/bin/bash
# mail-format.sh (ver. 1.1): Format e-mail messages.
# Gets rid of carets, tabs, and also folds excessively long lines.
# =================================================================
# Standard Check for Script Argument(s)
ARGS=1
E_BADARGS=65
E_NOFILE=66
if [ $# -ne $ARGS ] # Correct number of arguments passed to script?
then
echo "Usage: `basename $0` filename"
exit $E_BADARGS
fi
if [ -f "$1" ] # Check if file exists.
then
file_name=$1
else
echo "File \"$1\" does not exist."
exit $E_NOFILE
fi
# =================================================================
MAXWIDTH=70 # Width to fold excessively long lines to.
# ---------------------------------
# A variable can hold a sed script.
sedscript='s/^>//
s/^ *>//
s/^ *//
s/ *//'
# ---------------------------------
# Delete carets and tabs at beginning of lines,
#+ then fold lines to $MAXWIDTH characters.
sed "$sedscript" $1 | fold -s --width=$MAXWIDTH
# -s option to "fold"
#+ breaks lines at whitespace, if possible.
# This script was inspired by an article in a well-known trade journal
#+ extolling a 164K MS Windows utility with similar functionality.
#
# An nice set of text processing utilities and an efficient
#+ scripting language provide an alternative to bloated executables.
exit
Example A-2. rn: A simple-minded file renaming utility
This script is a modification of Example 16-22.
#! /bin/bash # rn.sh # Very simpleminded filename "rename" utility (based on "lowercase.sh"). # # The "ren" utility, by Vladimir Lanin ([email protected]), #+ does a much better job of this. ARGS=2 E_BADARGS=85 ONE=1 # For getting singular/plural right (see below). if [ $# -ne "$ARGS" ] then echo "Usage: `basename $0` old-pattern new-pattern" # As in "rn gif jpg", which renames all gif files in working directory to jpg. exit $E_BADARGS fi number=0 # Keeps track of how many files actually renamed. for filename in *$1* #Traverse all matching files in directory. do if [ -f "$filename" ] # If finds match... then fname=`basename $filename` # Strip off path. n=`echo $fname | sed -e "s/$1/$2/"` # Substitute new for old in filename. mv $fname $n # Rename. let "number += 1" fi done if [ "$number" -eq "$ONE" ] # For correct grammar. then echo "$number file renamed." else echo "$number files renamed." fi exit $? # Exercises: # --------- # What types of files will this not work on? # How can this be fixed?
Example A-3. blank-rename: Renames filenames containing blanks
This is an even simpler-minded version of previous script.
#! /bin/bash
# blank-rename.sh
#
# Substitutes underscores for blanks in all the filenames in a directory.
ONE=1 # For getting singular/plural right (see below).
number=0 # Keeps track of how many files actually renamed.
FOUND=0 # Successful return value.
for filename in * #Traverse all files in directory.
do
echo "$filename" | grep -q " " # Check whether filename
if [ $? -eq $FOUND ] #+ contains space(s).
then
fname=$filename # Yes, this filename needs work.
n=`echo $fname | sed -e "s/ /_/g"` # Substitute underscore for blank.
mv "$fname" "$n" # Do the actual renaming.
let "number += 1"
fi
done
if [ "$number" -eq "$ONE" ] # For correct grammar.
then
echo "$number file renamed."
else
echo "$number files renamed."
fi
exit 0
Example A-4. encryptedpw: Uploading to an ftp site, using a locally encrypted password
#!/bin/bash # Example "ex72.sh" modified to use encrypted password. # Note that this is still rather insecure, #+ since the decrypted password is sent in the clear. # Use something like "ssh" if this is a concern. E_BADARGS=85 if [ -z "$1" ] then echo "Usage: `basename $0` filename" exit $E_BADARGS fi Username=bozo # Change to suit. pword=/home/bozo/secret/password_encrypted.file # File containing encrypted password. Filename=`basename $1` # Strips pathname out of file name. Server="XXX" Directory="YYY" # Change above to actual server name & directory. Password=`cruft <$pword` # Decrypt password. # Uses the author's own "cruft" file encryption package, #+ based on the classic "onetime pad" algorithm, #+ and obtainable from: #+ Primary-site: ftp://ibiblio.org/pub/Linux/utils/file #+ cruft-0.2.tar.gz [16k] ftp -n $Server <<End-Of-Session user $Username $Password binary bell cd $Directory put $Filename bye End-Of-Session # -n option to "ftp" disables auto-logon. # Note that "bell" rings 'bell' after each file transfer. exit 0
Example A-5. copy-cd: Copying a data CD
#!/bin/bash
# copy-cd.sh: copying a data CD
CDROM=/dev/cdrom # CD ROM device
OF=/home/bozo/projects/cdimage.iso # output file
# /xxxx/xxxxxxxx/ Change to suit your system.
BLOCKSIZE=2048
# SPEED=10 # If unspecified, uses max spd.
# DEVICE=/dev/cdrom older version.
DEVICE="1,0,0"
echo; echo "Insert source CD, but do *not* mount it."
echo "Press ENTER when ready. "
read ready # Wait for input, $ready not used.
echo; echo "Copying the source CD to $OF."
echo "This may take a while. Please be patient."
dd if=$CDROM of=$OF bs=$BLOCKSIZE # Raw device copy.
echo; echo "Remove data CD."
echo "Insert blank CDR."
echo "Press ENTER when ready. "
read ready # Wait for input, $ready not used.
echo "Copying $OF to CDR."
# cdrecord -v -isosize speed=$SPEED dev=$DEVICE $OF # Old version.
wodim -v -isosize dev=$DEVICE $OF
# Uses Joerg Schilling's "cdrecord" package (see its docs).
# http://www.fokus.gmd.de/nthp/employees/schilling/cdrecord.html
# Newer Linux distros may use "wodim" rather than "cdrecord" ...
echo; echo "Done copying $OF to CDR on device $CDROM."
echo "Do you want to erase the image file (y/n)? " # Probably a huge file.
read answer
case "$answer" in
[yY]) rm -f $OF
echo "$OF erased."
;;
*) echo "$OF not erased.";;
esac
echo
# Exercise:
# Change the above "case" statement to also accept "yes" and "Yes" as input.
exit 0
Example A-6. Collatz series
#!/bin/bash
# collatz.sh
# The notorious "hailstone" or Collatz series.
# -------------------------------------------
# 1) Get the integer "seed" from the command-line.
# 2) NUMBER <-- seed
# 3) Print NUMBER.
# 4) If NUMBER is even, divide by 2, or
# 5)+ if odd, multiply by 3 and add 1.
# 6) NUMBER <-- result
# 7) Loop back to step 3 (for specified number of iterations).
#
# The theory is that every such sequence,
#+ no matter how large the initial value,
#+ eventually settles down to repeating "4,2,1..." cycles,
#+ even after fluctuating through a wide range of values.
#
# This is an instance of an "iterate,"
#+ an operation that feeds its output back into its input.
# Sometimes the result is a "chaotic" series.
MAX_ITERATIONS=200
# For large seed numbers (>32000), try increasing MAX_ITERATIONS.
h=${1:-$$} # Seed.
# Use $PID as seed,
#+ if not specified as command-line arg.
echo
echo "C($h) -*- $MAX_ITERATIONS Iterations"
echo
for ((i=1; i<=MAX_ITERATIONS; i++))
do
# echo -n "$h "
# ^^^
# tab
# printf does it better ...
COLWIDTH=%7d
printf $COLWIDTH $h
let "remainder = h % 2"
if [ "$remainder" -eq 0 ] # Even?
then
let "h /= 2" # Divide by 2.
else
let "h = h*3 + 1" # Multiply by 3 and add 1.
fi
COLUMNS=10 # Output 10 values per line.
let "line_break = i % $COLUMNS"
if [ "$line_break" -eq 0 ]
then
echo
fi
done
echo
# For more information on this strange mathematical function,
#+ see _Computers, Pattern, Chaos, and Beauty_, by Pickover, p. 185 ff.,
#+ as listed in the bibliography.
exit 0
Example A-7. days-between: Days between two dates
#!/bin/bash
# days-between.sh: Number of days between two dates.
# Usage: ./days-between.sh [M]M/[D]D/YYYY [M]M/[D]D/YYYY
#
# Note: Script modified to account for changes in Bash, v. 2.05b +,
#+ that closed the loophole permitting large negative
#+ integer return values.
ARGS=2 # Two command-line parameters expected.
E_PARAM_ERR=85 # Param error.
REFYR=1600 # Reference year.
CENTURY=100
DIY=365
ADJ_DIY=367 # Adjusted for leap year + fraction.
MIY=12
DIM=31
LEAPCYCLE=4
MAXRETVAL=255 # Largest permissible
#+ positive return value from a function.
diff= # Declare global variable for date difference.
value= # Declare global variable for absolute value.
day= # Declare globals for day, month, year.
month=
year=
Param_Error () # Command-line parameters wrong.
{
echo "Usage: `basename $0` [M]M/[D]D/YYYY [M]M/[D]D/YYYY"
echo " (date must be after 1/3/1600)"
exit $E_PARAM_ERR
}
Parse_Date () # Parse date from command-line params.
{
month=${1%%/**}
dm=${1%/**} # Day and month.
day=${dm#*/}
let "year = `basename $1`" # Not a filename, but works just the same.
}
check_date () # Checks for invalid date(s) passed.
{
[ "$day" -gt "$DIM" ] || [ "$month" -gt "$MIY" ] ||
[ "$year" -lt "$REFYR" ] && Param_Error
# Exit script on bad value(s).
# Uses or-list / and-list.
#
# Exercise: Implement more rigorous date checking.
}
strip_leading_zero () # Better to strip possible leading zero(s)
{ #+ from day and/or month
return ${1#0} #+ since otherwise Bash will interpret them
} #+ as octal values (POSIX.2, sect 2.9.2.1).
day_index () # Gauss' Formula:
{ # Days from March 1, 1600 to date passed as param.
# ^^^^^^^^^^^^^
day=$1
month=$2
year=$3
let "month = $month - 2"
if [ "$month" -le 0 ]
then
let "month += 12"
let "year -= 1"
fi
let "year -= $REFYR"
let "indexyr = $year / $CENTURY"
let "Days = $DIY*$year + $year/$LEAPCYCLE - $indexyr \
+ $indexyr/$LEAPCYCLE + $ADJ_DIY*$month/$MIY + $day - $DIM"
# For an in-depth explanation of this algorithm, see
#+ http://weblogs.asp.net/pgreborio/archive/2005/01/06/347968.aspx
echo $Days
}
calculate_difference () # Difference between two day indices.
{
let "diff = $1 - $2" # Global variable.
}
abs () # Absolute value
{ # Uses global "value" variable.
if [ "$1" -lt 0 ] # If negative
then #+ then
let "value = 0 - $1" #+ change sign,
else #+ else
let "value = $1" #+ leave it alone.
fi
}
if [ $# -ne "$ARGS" ] # Require two command-line params.
then
Param_Error
fi
Parse_Date $1
check_date $day $month $year # See if valid date.
strip_leading_zero $day # Remove any leading zeroes
day=$? #+ on day and/or month.
strip_leading_zero $month
month=$?
let "date1 = `day_index $day $month $year`"
Parse_Date $2
check_date $day $month $year
strip_leading_zero $day
day=$?
strip_leading_zero $month
month=$?
date2=$(day_index $day $month $year) # Command substitution.
calculate_difference $date1 $date2
abs $diff # Make sure it's positive.
diff=$value
echo $diff
exit 0
# Exercise:
# --------
# If given only one command-line parameter, have the script
#+ use today's date as the second.
# Compare this script with
#+ the implementation of Gauss' Formula in a C program at
#+ http://buschencrew.hypermart.net/software/datedif
Example A-8. Making a dictionary
#!/bin/bash
# makedict.sh [make dictionary]
# Modification of /usr/sbin/mkdict (/usr/sbin/cracklib-forman) script.
# Original script copyright 1993, by Alec Muffett.
#
# This modified script included in this document in a manner
#+ consistent with the "LICENSE" document of the "Crack" package
#+ that the original script is a part of.
# This script processes text files to produce a sorted list
#+ of words found in the files.
# This may be useful for compiling dictionaries
#+ and for other lexicographic purposes.
E_BADARGS=65
if [ ! -r "$1" ] # Need at least one
then #+ valid file argument.
echo "Usage: $0 files-to-process"
exit $E_BADARGS
fi
# SORT="sort" # No longer necessary to define
#+ options to sort. Changed from
#+ original script.
cat $* | # Contents of specified files to stdout.
tr A-Z a-z | # Convert to lowercase.
tr ' ' '\012' | # New: change spaces to newlines.
# tr -cd '\012[a-z][0-9]' | # Get rid of everything
#+ non-alphanumeric (in orig. script).
tr -c '\012a-z' '\012' | # Rather than deleting non-alpha
#+ chars, change them to newlines.
sort | # $SORT options unnecessary now.
uniq | # Remove duplicates.
grep -v '^#' | # Delete lines starting with hashmark.
grep -v '^$' # Delete blank lines.
exit 0
Example A-9. Soundex conversion
#!/bin/bash # soundex.sh: Calculate "soundex" code for names # ======================================================= # Soundex script # by # Mendel Cooper # [email protected] # reldate: 23 January, 2002 # # Placed in the Public Domain. # # A slightly different version of this script appeared in #+ Ed Schaefer's July, 2002 "Shell Corner" column #+ in "Unix Review" on-line, #+ http://www.unixreview.com/documents/uni1026336632258/ # ======================================================= ARGCOUNT=1 # Need name as argument. E_WRONGARGS=90 if [ $# -ne "$ARGCOUNT" ] then echo "Usage: `basename $0` name" exit $E_WRONGARGS fi assign_value () # Assigns numerical value { #+ to letters of name. val1=bfpv # 'b,f,p,v' = 1 val2=cgjkqsxz # 'c,g,j,k,q,s,x,z' = 2 val3=dt # etc. val4=l val5=mn val6=r # Exceptionally clever use of 'tr' follows. # Try to figure out what is going on here. value=$( echo "$1" \ | tr -d wh \ | tr $val1 1 | tr $val2 2 | tr $val3 3 \ | tr $val4 4 | tr $val5 5 | tr $val6 6 \ | tr -s 123456 \ | tr -d aeiouy ) # Assign letter values. # Remove duplicate numbers, except when separated by vowels. # Ignore vowels, except as separators, so delete them last. # Ignore 'w' and 'h', even as separators, so delete them first. # # The above command substitution lays more pipe than a plumber <g>. } input_name="$1" echo echo "Name = $input_name" # Change all characters of name input to lowercase. # ------------------------------------------------ name=$( echo $input_name | tr A-Z a-z ) # ------------------------------------------------ # Just in case argument to script is mixed case. # Prefix of soundex code: first letter of name. # -------------------------------------------- char_pos=0 # Initialize character position. prefix0=${name:$char_pos:1} prefix=`echo $prefix0 | tr a-z A-Z` # Uppercase 1st letter of soundex. let "char_pos += 1" # Bump character position to 2nd letter of name. name1=${name:$char_pos} # ++++++++++++++++++++++++++ Exception Patch ++++++++++++++++++++++++++++++ # Now, we run both the input name and the name shifted one char #+ to the right through the value-assigning function. # If we get the same value out, that means that the first two characters #+ of the name have the same value assigned, and that one should cancel. # However, we also need to test whether the first letter of the name #+ is a vowel or 'w' or 'h', because otherwise this would bollix things up. char1=`echo $prefix | tr A-Z a-z` # First letter of name, lowercased. assign_value $name s1=$value assign_value $name1 s2=$value assign_value $char1 s3=$value s3=9$s3 # If first letter of name is a vowel #+ or 'w' or 'h', #+ then its "value" will be null (unset). #+ Therefore, set it to 9, an otherwise #+ unused value, which can be tested for. if [[ "$s1" -ne "$s2" || "$s3" -eq 9 ]] then suffix=$s2 else suffix=${s2:$char_pos} fi # ++++++++++++++++++++++ end Exception Patch ++++++++++++++++++++++++++++++ padding=000 # Use at most 3 zeroes to pad. soun=$prefix$suffix$padding # Pad with zeroes. MAXLEN=4 # Truncate to maximum of 4 chars. soundex=${soun:0:$MAXLEN} echo "Soundex = $soundex" echo # The soundex code is a method of indexing and classifying names #+ by grouping together the ones that sound alike. # The soundex code for a given name is the first letter of the name, #+ followed by a calculated three-number code. # Similar sounding names should have almost the same soundex codes. # Examples: # Smith and Smythe both have a "S-530" soundex. # Harrison = H-625 # Hargison = H-622 # Harriman = H-655 # This works out fairly well in practice, but there are numerous anomalies. # # # The U.S. Census and certain other governmental agencies use soundex, # as do genealogical researchers. # # For more information, #+ see the "National Archives and Records Administration home page", #+ http://www.nara.gov/genealogy/soundex/soundex.html # Exercise: # -------- # Simplify the "Exception Patch" section of this script. exit 0
Example A-10. Game of Life
#!/bin/bash
# life.sh: "Life in the Slow Lane"
# Author: Mendel Cooper
# License: GPL3
# Version 0.2: Patched by Daniel Albers
#+ to allow non-square grids as input.
# Version 0.2.1: Added 2-second delay between generations.
# ##################################################################### #
# This is the Bash script version of John Conway's "Game of Life". #
# "Life" is a simple implementation of cellular automata. #
# --------------------------------------------------------------------- #
# On a rectangular grid, let each "cell" be either "living" or "dead." #
# Designate a living cell with a dot, and a dead one with a blank space.#
# Begin with an arbitrarily drawn dot-and-blank grid, #
#+ and let this be the starting generation: generation 0. #
# Determine each successive generation by the following rules: #
# 1) Each cell has 8 neighbors, the adjoining cells #
#+ left, right, top, bottom, and the 4 diagonals. #
# #
# 123 #
# 4*5 The * is the cell under consideration. #
# 678 #
# #
# 2) A living cell with either 2 or 3 living neighbors remains alive. #
SURVIVE=2 #
# 3) A dead cell with 3 living neighbors comes alive, a "birth." #
BIRTH=3 #
# 4) All other cases result in a dead cell for the next generation. #
# ##################################################################### #
startfile=gen0 # Read the starting generation from the file "gen0" ...
# Default, if no other file specified when invoking script.
#
if [ -n "$1" ] # Specify another "generation 0" file.
then
startfile="$1"
fi
############################################
# Abort script if "startfile" not specified
#+ and
#+ default file "gen0" not present.
E_NOSTARTFILE=86
if [ ! -e "$startfile" ]
then
echo "Startfile \""$startfile"\" missing!"
exit $E_NOSTARTFILE
fi
############################################
ALIVE1=.
DEAD1=_
# Represent living and dead cells in the start-up file.
# -----------------------------------------------------#
# This script uses a 10 x 10 grid (may be increased,
#+ but a large grid will slow down execution).
ROWS=10
COLS=10
# Change above two variables to match desired grid size.
# -----------------------------------------------------#
GENERATIONS=10 # How many generations to cycle through.
# Adjust this upwards
#+ if you have time on your hands.
NONE_ALIVE=85 # Exit status on premature bailout,
#+ if no cells left alive.
DELAY=2 # Pause between generations.
TRUE=0
FALSE=1
ALIVE=0
DEAD=1
avar= # Global; holds current generation.
generation=0 # Initialize generation count.
# =================================================================
let "cells = $ROWS * $COLS" # How many cells.
# Arrays containing "cells."
declare -a initial
declare -a current
display ()
{
alive=0 # How many cells alive at any given time.
# Initially zero.
declare -a arr
arr=( `echo "$1"` ) # Convert passed arg to array.
element_count=${#arr[*]}
local i
local rowcheck
for ((i=0; i<$element_count; i++))
do
# Insert newline at end of each row.
let "rowcheck = $i % COLS"
if [ "$rowcheck" -eq 0 ]
then
echo # Newline.
echo -n " " # Indent.
fi
cell=${arr[i]}
if [ "$cell" = . ]
then
let "alive += 1"
fi
echo -n "$cell" | sed -e 's/_/ /g'
# Print out array, changing underscores to spaces.
done
return
}
IsValid () # Test if cell coordinate valid.
{
if [ -z "$1" -o -z "$2" ] # Mandatory arguments missing?
then
return $FALSE
fi
local row
local lower_limit=0 # Disallow negative coordinate.
local upper_limit
local left
local right
let "upper_limit = $ROWS * $COLS - 1" # Total number of cells.
if [ "$1" -lt "$lower_limit" -o "$1" -gt "$upper_limit" ]
then
return $FALSE # Out of array bounds.
fi
row=$2
let "left = $row * $COLS" # Left limit.
let "right = $left + $COLS - 1" # Right limit.
if [ "$1" -lt "$left" -o "$1" -gt "$right" ]
then
return $FALSE # Beyond row boundary.
fi
return $TRUE # Valid coordinate.
}
IsAlive () # Test whether cell is alive.
# Takes array, cell number, and
{ #+ state of cell as arguments.
GetCount "$1" $2 # Get alive cell count in neighborhood.
local nhbd=$?
if [ "$nhbd" -eq "$BIRTH" ] # Alive in any case.
then
return $ALIVE
fi
if [ "$3" = "." -a "$nhbd" -eq "$SURVIVE" ]
then # Alive only if previously alive.
return $ALIVE
fi
return $DEAD # Defaults to dead.
}
GetCount () # Count live cells in passed cell's neighborhood.
# Two arguments needed:
# $1) variable holding array
# $2) cell number
{
local cell_number=$2
local array
local top
local center
local bottom
local r
local row
local i
local t_top
local t_cen
local t_bot
local count=0
local ROW_NHBD=3
array=( `echo "$1"` )
let "top = $cell_number - $COLS - 1" # Set up cell neighborhood.
let "center = $cell_number - 1"
let "bottom = $cell_number + $COLS - 1"
let "r = $cell_number / $COLS"
for ((i=0; i<$ROW_NHBD; i++)) # Traverse from left to right.
do
let "t_top = $top + $i"
let "t_cen = $center + $i"
let "t_bot = $bottom + $i"
let "row = $r" # Count center row.
IsValid $t_cen $row # Valid cell position?
if [ $? -eq "$TRUE" ]
then
if [ ${array[$t_cen]} = "$ALIVE1" ] # Is it alive?
then # If yes, then ...
let "count += 1" # Increment count.
fi
fi
let "row = $r - 1" # Count top row.
IsValid $t_top $row
if [ $? -eq "$TRUE" ]
then
if [ ${array[$t_top]} = "$ALIVE1" ] # Redundancy here.
then # Can it be optimized?
let "count += 1"
fi
fi
let "row = $r + 1" # Count bottom row.
IsValid $t_bot $row
if [ $? -eq "$TRUE" ]
then
if [ ${array[$t_bot]} = "$ALIVE1" ]
then
let "count += 1"
fi
fi
done
if [ ${array[$cell_number]} = "$ALIVE1" ]
then
let "count -= 1" # Make sure value of tested cell itself
fi #+ is not counted.
return $count
}
next_gen () # Update generation array.
{
local array
local i=0
array=( `echo "$1"` ) # Convert passed arg to array.
while [ "$i" -lt "$cells" ]
do
IsAlive "$1" $i ${array[$i]} # Is the cell alive?
if [ $? -eq "$ALIVE" ]
then # If alive, then
array[$i]=. #+ represent the cell as a period.
else
array[$i]="_" # Otherwise underscore
fi #+ (will later be converted to space).
let "i += 1"
done
# let "generation += 1" # Increment generation count.
### Why was the above line commented out?
# Set variable to pass as parameter to "display" function.
avar=`echo ${array[@]}` # Convert array back to string variable.
display "$avar" # Display it.
echo; echo
echo "Generation $generation - $alive alive"
if [ "$alive" -eq 0 ]
then
echo
echo "Premature exit: no more cells alive!"
exit $NONE_ALIVE # No point in continuing
fi #+ if no live cells.
}
# =========================================================
# main ()
# {
# Load initial array with contents of startup file.
initial=( `cat "$startfile" | sed -e '/#/d' | tr -d '\n' |\
# Delete lines containing '#' comment character.
sed -e 's/\./\. /g' -e 's/_/_ /g'` )
# Remove linefeeds and insert space between elements.
clear # Clear screen.
echo # Title
setterm -reverse on
echo "======================="
setterm -reverse off
echo " $GENERATIONS generations"
echo " of"
echo "\"Life in the Slow Lane\""
setterm -reverse on
echo "======================="
setterm -reverse off
sleep $DELAY # Display "splash screen" for 2 seconds.
# -------- Display first generation. --------
Gen0=`echo ${initial[@]}`
display "$Gen0" # Display only.
echo; echo
echo "Generation $generation - $alive alive"
sleep $DELAY
# -------------------------------------------
let "generation += 1" # Bump generation count.
echo
# ------- Display second generation. -------
Cur=`echo ${initial[@]}`
next_gen "$Cur" # Update & display.
sleep $DELAY
# ------------------------------------------
let "generation += 1" # Increment generation count.
# ------ Main loop for displaying subsequent generations ------
while [ "$generation" -le "$GENERATIONS" ]
do
Cur="$avar"
next_gen "$Cur"
let "generation += 1"
sleep $DELAY
done
# ==============================================================
echo
# }
exit 0 # CEOF:EOF
# The grid in this script has a "boundary problem."
# The the top, bottom, and sides border on a void of dead cells.
# Exercise: Change the script to have the grid wrap around,
# + so that the left and right sides will "touch,"
# + as will the top and bottom.
#
# Exercise: Create a new "gen0" file to seed this script.
# Use a 12 x 16 grid, instead of the original 10 x 10 one.
# Make the necessary changes to the script,
#+ so it will run with the altered file.
#
# Exercise: Modify this script so that it can determine the grid size
#+ from the "gen0" file, and set any variables necessary
#+ for the script to run.
# This would make unnecessary any changes to variables
#+ in the script for an altered grid size.
#
# Exercise: Optimize this script.
# It has redundant code.
Example A-11. Data file for Game of Life
# gen0 # # This is an example "generation 0" start-up file for "life.sh". # -------------------------------------------------------------- # The "gen0" file is a 10 x 10 grid using a period (.) for live cells, #+ and an underscore (_) for dead ones. We cannot simply use spaces #+ for dead cells in this file because of a peculiarity in Bash arrays. # [Exercise for the reader: explain this.] # # Lines beginning with a '#' are comments, and the script ignores them. __.__..___ __.._.____ ____.___.. _._______. ____._____ ..__...___ ____._____ ___...____ __.._..___ _..___..__
+++
The following script is by Mark Moraes of the University of Toronto. See the file Moraes-COPYRIGHT for permissions and restrictions. This file is included in the combined HTML/source tarball of the ABS Guide.
Example A-12. behead: Removing mail and news message headers
About AquaClusters Privacy Policy Support Version - 19.0.2-4 AquaFold, Inc Copyright © 2007-2017