Contributed ScriptsThese scripts, while not fitting into the text of this document, do
illustrate some interesting shell programming techniques. They are useful,
too. Have fun analyzing and running them. Example A-1. manview: Viewing formatted manpages
#!/bin/bash
# manview.sh: Formats the source of a man page for viewing.
# This is useful when writing man page source and you want to
#+ look at the intermediate results on the fly while working on it.
E_WRONGARGS=65
if [ -z "$1" ]
then
echo "Usage: `basename $0` filename"
exit $E_WRONGARGS
fi
groff -Tascii -man $1 | less
# From the man page for groff.
# If the man page includes tables and/or equations,
# then the above code will barf.
# The following line can handle such cases.
#
# gtbl < "$1" | geqn -Tlatin1 | groff -Tlatin1 -mtty-char -man
#
# Thanks, S.C.
exit 0 |
Example A-2. mailformat: Formatting an e-mail message #!/bin/bash
# mail-format.sh: Format e-mail messages.
# Gets rid of carets, tabs, also fold 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 long lines to.
# Delete carets and tabs at beginning of lines,
#+ then fold lines to $MAXWIDTH characters.
sed '
s/^>//
s/^ *>//
s/^ *//
s/ *//
' $1 | fold -s --width=$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 Windows utility with similar functionality.
#
# An nice set of text processing utilities and an efficient
#+ scripting language provide an alternative to bloated executables.
exit 0 |
Example A-3. rn: A simple-minded file rename utility This script is a modification of Example 12-15. #! /bin/bash
#
# Very simpleminded filename "rename" utility (based on "lowercase.sh").
#
# The "ren" utility, by Vladimir Lanin (lanin@csd2.nyu.edu),
#+ does a much better job of this.
ARGS=2
E_BADARGS=65
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 "$number files renamed."
fi
exit 0
# Exercises:
# ---------
# What type of files will this not work on?
# How can this be fixed?
#
# Rewrite this script to process all the files in a directory
#+ containing spaces in their names, and to rename them,
#+ substituting an underscore for each space. |
Example A-4. blank-rename: renames filenames containing
blanks This is an even simpler-minded version of previous script. #! /bin/bash
# blank-rename.sh
#
# Substitutes underscores for blanks in all the filenames in a directory.
ONE=1 # For getting singular/plural right (see below).
number=0 # Keeps track of how many files actually renamed.
FOUND=0 # Successful return value.
for filename in * #Traverse all files in directory.
do
echo "$filename" | grep -q " " # Check whether filename
if [ $? -eq $FOUND ] #+ contains space(s).
then
fname=$filename # Strip off path.
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-5. 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 somewhat insecure,
#+ since the decrypted password is sent in the clear.
# Use something like "ssh" if this is a concern.
E_BADARGS=65
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://metalab.unc.edu /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.
# "bell" rings 'bell' after each file transfer.
exit 0 |
Example A-6. 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/xxxxxxx/ Change to suit your system.
BLOCKSIZE=2048
SPEED=2 # May use higher speed if supported.
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=0,0 $OF
# Uses Joerg Schilling's "cdrecord" package (see its docs).
# http://www.fokus.gmd.de/nthp/employees/schilling/cdrecord&.html
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 "$OF not erased.";;
esac
echo
# Exercise:
# Change the above "case" statement to also accept "yes" and "Yes" as input.
exit 0 |
Example A-7. Collatz series #!/bin/bash
# collatz.sh
# The notorious "hailstone" or Collatz series.
# -------------------------------------------
# 1) Get the integer "seed" from the command line.
# 2) NUMBER <--- seed
# 3) Print NUMBER.
# 4) If NUMBER is even, divide by 2, or
# 5)+ if odd, multiply by 3 and add 1.
# 6) NUMBER <--- result
# 7) Loop back to step 3 (for specified number of iterations).
#
# The theory is that every sequence,
#+ no matter how large the initial value,
#+ eventually settles down to repeating "4,2,1..." cycles,
#+ even after fluctuating through a wide range of values.
#
# This is an instance of an "iterate",
#+ an operation that feeds its output back into the input.
# Sometimes the result is a "chaotic" series.
MAX_ITERATIONS=200
# For large seed numbers (>32000), increase MAX_ITERATIONS.
h=${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
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 mathematical function,
#+ see "Computers, Pattern, Chaos, and Beauty", by Pickover, p. 185 ff.,
#+ as listed in the bibliography.
exit 0 |
Example A-8. days-between: Calculate number of 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
ARGS=2 # Two command line parameters expected.
E_PARAM_ERR=65 # 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=256 # Largest permissable
# 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
val=${1#0} # since otherwise Bash will interpret them
return $val # as octal values (POSIX.2, sect 2.9.2.1).
}
day_index () # Gauss' Formula:
{ # Days from Jan. 3, 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://home.t-online.de/home/berndt.schwerdtfeger/cal.htm
if [ "$Days" -gt "$MAXRETVAL" ] # If greater than 256,
then # then change to negative value
let "dindex = 0 - $Days" # which can be returned from function.
else let "dindex = $Days"
fi
return $dindex
}
calculate_difference () # Difference between to 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=$?
day_index $day $month $year
date1=$?
abs $date1 # Make sure it's positive
date1=$value # by getting absolute value.
Parse_Date $2
check_date $day $month $year
strip_leading_zero $day
day=$?
strip_leading_zero $month
month=$?
day_index $day $month $year
date2=$?
abs $date2 # Make sure it's positive.
date2=$value
calculate_difference $date1 $date2
abs $diff # Make sure it's positive.
diff=$value
echo $diff
exit 0
# Compare this script with the implementation of Gauss' Formula in C at
# http://buschencrew.hypermart.net/software/datedif |
Example A-9. Make a "dictionary" #!/bin/bash
# makedict.sh [make dictionary]
# Modification of /usr/sbin/mkdict 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 lexicographic research.
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 uppercase.
tr ' ' '\012' | # New: change spaces to newlines.
# tr -cd '\012[a-z][0-9]' | # Get rid of everything non-alphanumeric
#+ (original script).
tr -c '\012a-z' '\012' | # Rather than deleting
#+ now change non-alpha to newlines.
sort | # $SORT options unnecessary now.
uniq | # Remove duplicates.
grep -v '^#' | # Delete lines beginning with a hashmark.
grep -v '^$' # Delete blank lines.
exit 0 |
Example A-10. Soundex conversion #!/bin/bash
# soundex.sh: Calculate "soundex" code for names
# =======================================================
# Soundex script
# by
# Mendel Cooper
# thegrendel@theriver.com
# 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=70
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-11. "Game of Life" #!/bin/bash
# life.sh: "Life in the Slow Lane"
# ##################################################################### #
# 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 #
# 678 #
# #
# 2) A living cell with either 2 or 3 living neighbors remains alive. #
# 3) A dead cell with 3 living neighbors becomes alive (a "birth"). #
SURVIVE=2 #
BIRTH=3 #
# 4) All other cases result in dead cells. #
# ##################################################################### #
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
if [ -e "$1" ] # Check for existence.
then
startfile="$1"
fi
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 will cause very slow execution).
ROWS=10
COLS=10
GENERATIONS=10 # How many generations to cycle through.
# Adjust this upwards,
#+ if you have time on your hands.
NONE_ALIVE=80 # Exit status on premature bailout,
#+ if no cells left alive.
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.
declare -a initial # Arrays containing "cells".
declare -a current
display ()
{
alive=0 # How many cells "alive".
# 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 % ROWS"
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 and change underscores to spaces.
done
return
}
IsValid () # Test whether 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 * $ROWS" # 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, 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 # Default.
}
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 / $ROWS"
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 of neighborhood.
IsValid $t_cen $row # Valid cell position?
if [ $? -eq "$TRUE" ]
then
if [ ${array[$t_cen]} = "$ALIVE1" ] # Is it alive?
then # Yes?
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" ]
then
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 cell alive?
if [ $? -eq "$ALIVE" ]
then # If alive, then
array[$i]=. #+ represent the cell as a period.
else
array[$i]="_" # Otherwise underscore
fi #+ (which will later be converted to space).
let "i += 1"
done
# let "generation += 1" # Increment generation count.
# 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' |\
sed -e 's/\./\. /g' -e 's/_/_ /g'` )
# Delete lines containing '#' comment character.
# Remove linefeeds and insert space between elements.
clear # Clear screen.
echo # Title
echo "======================="
echo " $GENERATIONS generations"
echo " of"
echo "\"Life in the Slow Lane\""
echo "======================="
# -------- Display first generation. --------
Gen0=`echo ${initial[@]}`
display "$Gen0" # Display only.
echo; echo
echo "Generation $generation -- $alive alive"
# -------------------------------------------
let "generation += 1" # Increment generation count.
echo
# ------- Display second generation. -------
Cur=`echo ${initial[@]}`
next_gen "$Cur" # Update & display.
# ------------------------------------------
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"
done
# ==============================================================
echo
exit 0
# --------------------------------------------------------------
# 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. |
Example A-12. Data file for "Game of Life" # 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 two scripts are by Mark Moraes of the University
of Toronto. See the enclosed file "Moraes-COPYRIGHT"
for permissions and restrictions. Example A-13. behead: Removing mail and news message headers
#! /bin/sh
# Strips off the header from a mail/News message i.e. till the first
# empty line
# Mark Moraes, University of Toronto
# ==> These comments added by author of this document.
if [ $# -eq 0 ]; then
# ==> If no command line args present, then works on file redirected to stdin.
sed -e '1,/^$/d' -e '/^[ ]*$/d'
# --> Delete empty lines and all lines until
# --> first one beginning with white space.
else
# ==> If command line args present, then work on files named.
for i do
sed -e '1,/^$/d' -e '/^[ ]*$/d' $i
# --> Ditto, as above.
done
fi
# ==> Exercise: Add error checking and other options.
# ==>
# ==> Note that the small sed script repeats, except for the arg passed.
# ==> Does it make sense to embed it in a function? Why or why not? |
Example A-14. ftpget: Downloading files via ftp
#! /bin/sh
# $Id: ftpget,v 1.2 91/05/07 21:15:43 moraes Exp $
# Script to perform batch anonymous ftp. Essentially converts a list of
# of command line arguments into input to ftp.
# Simple, and quick - written as a companion to ftplist
# -h specifies the remote host (default prep.ai.mit.edu)
# -d specifies the remote directory to cd to - you can provide a sequence
# of -d options - they will be cd'ed to in turn. If the paths are relative,
# make sure you get the sequence right. Be careful with relative paths -
# there are far too many symlinks nowadays.
# (default is the ftp login directory)
# -v turns on the verbose option of ftp, and shows all responses from the
# ftp server.
# -f remotefile[:localfile] gets the remote file into localfile
# -m pattern does an mget with the specified pattern. Remember to quote
# shell characters.
# -c does a local cd to the specified directory
# For example,
# ftpget -h expo.lcs.mit.edu -d contrib -f xplaces.shar:xplaces.sh \
# -d ../pub/R3/fixes -c ~/fixes -m 'fix*'
# will get xplaces.shar from ~ftp/contrib on expo.lcs.mit.edu, and put it in
# xplaces.sh in the current working directory, and get all fixes from
# ~ftp/pub/R3/fixes and put them in the ~/fixes directory.
# Obviously, the sequence of the options is important, since the equivalent
# commands are executed by ftp in corresponding order
#
# Mark Moraes (moraes@csri.toronto.edu), Feb 1, 1989
# ==> Angle brackets changed to parens, so Docbook won't get indigestion.
#
# ==> These comments added by author of this document.
# PATH=/local/bin:/usr/ucb:/usr/bin:/bin
# export PATH
# ==> Above 2 lines from original script probably superfluous.
TMPFILE=/tmp/ftp.$$
# ==> Creates temp file, using process id of script ($$)
# ==> to construct filename.
SITE=`domainname`.toronto.edu
# ==> 'domainname' similar to 'hostname'
# ==> May rewrite this to parameterize this for general use.
usage="Usage: $0 [-h remotehost] [-d remotedirectory]... [-f remfile:localfile]... \
[-c localdirectory] [-m filepattern] [-v]"
ftpflags="-i -n"
verbflag=
set -f # So we can use globbing in -m
set x `getopt vh:d:c:m:f: $*`
if [ $? != 0 ]; then
echo $usage
exit 65
fi
shift
trap 'rm -f ${TMPFILE} ; exit' 0 1 2 3 15
echo "user anonymous ${USER-gnu}@${SITE} > ${TMPFILE}"
# ==> Added quotes (recommended in complex echoes).
echo binary >> ${TMPFILE}
for i in $* # ==> Parse command line args.
do
case $i in
-v) verbflag=-v; echo hash >> ${TMPFILE}; shift;;
-h) remhost=$2; shift 2;;
-d) echo cd $2 >> ${TMPFILE};
if [ x${verbflag} != x ]; then
echo pwd >> ${TMPFILE};
fi;
shift 2;;
-c) echo lcd $2 >> ${TMPFILE}; shift 2;;
-m) echo mget "$2" >> ${TMPFILE}; shift 2;;
-f) f1=`expr "$2" : "\([^:]*\).*"`; f2=`expr "$2" : "[^:]*:\(.*\)"`;
echo get ${f1} ${f2} >> ${TMPFILE}; shift 2;;
--) shift; break;;
esac
done
if [ $# -ne 0 ]; then
echo $usage
exit 65 # ==> Changed from "exit 2" to conform with standard.
fi
if [ x${verbflag} != x ]; then
ftpflags="${ftpflags} -v"
fi
if [ x${remhost} = x ]; then
remhost=prep.ai.mit.edu
# ==> Rewrite to match your favorite ftp site.
fi
echo quit >> ${TMPFILE}
# ==> All commands saved in tempfile.
ftp ${ftpflags} ${remhost} < ${TMPFILE}
# ==> Now, tempfile batch processed by ftp.
rm -f ${TMPFILE}
# ==> Finally, tempfile deleted (you may wish to copy it to a logfile).
# ==> Exercises:
# ==> ---------
# ==> 1) Add error checking.
# ==> 2) Add bells & whistles. |
+ Antek Sawicki contributed the following script, which makes very
clever use of the parameter substitution operators discussed in
Section 9.3. Example A-15. password: Generating random
8-character passwords #!/bin/bash
# May need to be invoked with #!/bin/bash2 on older machines.
#
# Random password generator for bash 2.x by Antek Sawicki <tenox@tenox.tc>,
# who generously gave permission to the document author to use it here.
#
# ==> Comments added by document author ==>
MATRIX="0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz"
LENGTH="8"
# ==> May change 'LENGTH' for longer password, of course.
while [ "${n:=1}" -le "$LENGTH" ]
# ==> Recall that := is "default substitution" operator.
# ==> So, if 'n' has not been initialized, set it to 1.
do
PASS="$PASS${MATRIX:$(($RANDOM%${#MATRIX})):1}"
# ==> Very clever, but tricky.
# ==> Starting from the innermost nesting...
# ==> ${#MATRIX} returns length of array MATRIX.
# ==> $RANDOM%${#MATRIX} returns random number between 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.
# ==> PASS=... simply pastes this result onto previous PASS (concatenation).
# ==> To visualize this more clearly, uncomment the following line
# ==> echo "$PASS"
# ==> to see PASS being built up,
# ==> one character at a time, each iteration of the loop.
let n+=1
# ==> Increment 'n' for next pass.
done
echo "$PASS" # ==> Or, redirect to file, as desired.
exit 0 |
+ James R. Van Zandt contributed this script, which uses named pipes
and, in his words, "really exercises quoting and escaping".
Example A-16. fifo: Making daily backups, using named pipes #!/bin/bash
# ==> Script by James R. Van Zandt, and used here with his permission.
# ==> Comments added by author of this document.
HERE=`uname -n` # ==> hostname
THERE=bilbo
echo "starting remote backup to $THERE at `date +%r`"
# ==> `date +%r` returns time in 12-hour format, i.e. "08:08:34 PM".
# make sure /pipe really is a pipe and not a plain file
rm -rf /pipe
mkfifo /pipe # ==> Create a "named pipe", named "/pipe".
# ==> 'su xyz' runs commands as user "xyz".
# ==> 'ssh' invokes secure shell (remote login client).
su xyz -c "ssh $THERE \"cat >/home/xyz/backup/${HERE}-daily.tar.gz\" < /pipe"&
cd /
tar -czf - bin boot dev etc home info lib man root sbin share usr var >/pipe
# ==> Uses named pipe, /pipe, to communicate between processes:
# ==> 'tar/gzip' writes to /pipe and 'ssh' reads from /pipe.
# ==> The end result is this backs up the main directories, from / on down.
# ==> What are the advantages of a "named pipe" in this situation,
# ==> as opposed to an "anonymous pipe", with |?
# ==> Will an anonymous pipe even work here?
exit 0 |
+ Stephane Chazelas contributed the following script to
demonstrate that generating prime numbers does not require
arrays. Example A-17. Generating prime numbers using the modulo operator #!/bin/bash
# primes.sh: Generate prime numbers, without using arrays.
# Script contributed by Stephane Chazelas.
# This does *not* use the classic "Sieve of Eratosthenes" algorithm,
#+ but instead uses the more intuitive method of testing each candidate number
#+ for factors (divisors), using the "%" modulo operator.
LIMIT=1000 # Primes 2 - 1000
Primes()
{
(( n = $1 + 1 )) # Bump to next integer.
shift # Next parameter in list.
# echo "_n=$n i=$i_"
if (( n == LIMIT ))
then echo $*
return
fi
for i; do # "i" gets set to "@", previous values of $n.
# echo "-n=$n i=$i-"
(( i * i > n )) && break # Optimization.
(( n % i )) && continue # Sift out non-primes using modulo operator.
Primes $n $@ # Recursion inside loop.
return
done
Primes $n $@ $n # Recursion outside loop.
# Successively accumulate positional parameters.
# "$@" is the accumulating list of primes.
}
Primes 1
exit 0
# Uncomment lines 17 and 25 to help figure out what is going on.
# Compare the speed of this algorithm for generating primes
# with the Sieve of Eratosthenes (ex68.sh).
# Exercise: Rewrite this script without recursion, for faster execution. |
+ Jordi Sanfeliu gave permission to use his elegant
tree script. Example A-18. tree: Displaying a directory tree #!/bin/sh
# @(#) tree 1.1 30/11/95 by Jordi Sanfeliu
# email: mikaku@arrakis.es
#
# 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 :-) )
#
# ==> '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 $numdirs + 1` # ==> Increment directory count.
fi
fi
fi
done
cd .. # ==> Up one directory level.
if [ "$deep" ] ; then # ==> If depth = 0 (returns TRUE)...
swfi=1 # ==> set flag showing that search is done.
fi
deep=`expr $deep - 1` # ==> Decrement depth.
}
# - Main -
if [ $# = 0 ] ; then
cd `pwd` # ==> No args to script, then use current working directory.
else
cd $1 # ==> Otherwise, move to indicated directory.
fi
echo "Initial directory = `pwd`"
swfi=0 # ==> Search finished flag.
deep=0 # ==> Depth of listing.
numdirs=0
zz=0
while [ "$swfi" != 1 ] # While flag not set...
do
search # ==> Call function after initializing variables.
done
echo "Total directories = $numdirs"
exit 0
# ==> Challenge: try to figure out exactly how this script works. |
Noah Friedman gave permission to use his string
function script, which essentially reproduces some of the
C-library string manipulation functions. Example A-19. string functions: C-like string functions #!/bin/bash
# string.bash --- bash emulation of string(3) library routines
# Author: Noah Friedman <friedman@prep.ai.mit.edu>
# ==> Used with his kind permission in this document.
# Created: 1992-07-01
# Last modified: 1993-09-29
# Public domain
# Conversion to bash v2 syntax done by Chet Ramey
# Commentary:
# Code:
#:docstring strcat:
# Usage: strcat s1 s2
#
# Strcat appends the value of variable s2 to variable s1.
#
# Example:
# a="foo"
# b="bar"
# strcat a b
# echo $a
# => foobar
#
#:end docstring:
###;;;autoload ==> Autoloading of function commented out.
function strcat ()
{
local s1_val s2_val
s1_val=${!1} # indirect variable expansion
s2_val=${!2}
eval "$1"=\'"${s1_val}${s2_val}"\'
# ==> eval $1='${s1_val}${s2_val}' avoids problems,
# ==> if one of the variables contains a single quote.
}
#:docstring strncat:
# Usage: strncat s1 s2 $n
#
# Line strcat, but strncat appends a maximum of n characters from the value
# of variable s2. It copies fewer if the value of variabl s2 is shorter
# than n characters. Echoes result on stdout.
#
# Example:
# a=foo
# b=barbaz
# strncat a b 3
# echo $a
# => foobar
#
#:end docstring:
###;;;autoload
function strncat ()
{
local s1="$1"
local s2="$2"
local -i n="$3"
local s1_val s2_val
s1_val=${!s1} # ==> indirect variable expansion
s2_val=${!s2}
if [ ${#s2_val} -gt ${n} ]; then
s2_val=${s2_val:0:$n} # ==> substring extraction
fi
eval "$s1"=\'"${s1_val}${s2_val}"\'
# ==> eval $1='${s1_val}${s2_val}' avoids problems,
# ==> if one of the variables contains a single quote.
}
#:docstring strcmp:
# Usage: strcmp $s1 $s2
#
# Strcmp compares its arguments and returns an integer less than, equal to,
# or greater than zero, depending on whether string s1 is lexicographically
# less than, equal to, or greater than string s2.
#:end docstring:
###;;;autoload
function strcmp ()
{
[ "$1" = "$2" ] && return 0
[ "${1}" '<' "${2}" ] > /dev/null && return -1
return 1
}
#:docstring strncmp:
# Usage: strncmp $s1 $s2 $n
#
# Like strcmp, but makes the comparison by examining a maximum of n
# characters (n less than or equal to zero yields equality).
#:end docstring:
###;;;autoload
function strncmp ()
{
if [ -z "${3}" -o "${3}" -le "0" ]; then
return 0
fi
if [ ${3} -ge ${#1} -a ${3} -ge ${#2} ]; then
strcmp "$1" "$2"
return $?
else
s1=${1:0:$3}
s2=${2:0:$3}
strcmp $s1 $s2
return $?
fi
}
#:docstring strlen:
# Usage: strlen s
#
# Strlen returns the number of characters in string literal s.
#:end docstring:
###;;;autoload
function strlen ()
{
eval echo "\${#${1}}"
# ==> Returns the length of the value of the variable
# ==> whose name is passed as an argument.
}
#:docstring strspn:
# Usage: strspn $s1 $s2
#
# Strspn returns the length of the maximum initial segment of string s1,
# which consists entirely of characters from string s2.
#:end docstring:
###;;;autoload
function strspn ()
{
# Unsetting IFS allows whitespace to be handled as normal chars.
local IFS=
local result="${1%%[!${2}]*}"
echo ${#result}
}
#:docstring strcspn:
# Usage: strcspn $s1 $s2
#
# Strcspn returns the length of the maximum initial segment of string s1,
# which consists entirely of characters not from string s2.
#:end docstring:
###;;;autoload
function strcspn ()
{
# Unsetting IFS allows whitspace to be handled as normal chars.
local IFS=
local result="${1%%[${2}]*}"
echo ${#result}
}
#:docstring strstr:
# Usage: strstr s1 s2
#
# Strstr echoes a substring starting at the first occurrence of string s2 in
# string s1, or nothing if s2 does not occur in the string. If s2 points to
# a string of zero length, strstr echoes s1.
#:end docstring:
###;;;autoload
function strstr ()
{
# if s2 points to a string of zero length, strstr echoes s1
[ ${#2} -eq 0 ] && { echo "$1" ; return 0; }
# strstr echoes nothing if s2 does not occur in s1
case "$1" in
*$2*) ;;
*) return 1;;
esac
# use the pattern matching code to strip off the match and everything
# following it
first=${1/$2*/}
# then strip off the first unmatched portion of the string
echo "${1##$first}"
}
#:docstring strtok:
# Usage: strtok s1 s2
#
# Strtok considers the string s1 to consist of a sequence of zero or more
# text tokens separated by spans of one or more characters from the
# separator string s2. The first call (with a non-empty string s1
# specified) echoes a string consisting of the first token on stdout. The
# function keeps track of its position in the string s1 between separate
# calls, so that subsequent calls made with the first argument an empty
# string will work through the string immediately following that token. In
# this way subsequent calls will work through the string s1 until no tokens
# remain. The separator string s2 may be different from call to call.
# When no token remains in s1, an empty value is echoed on stdout.
#:end docstring:
###;;;autoload
function strtok ()
{
:
}
#:docstring strtrunc:
# Usage: strtrunc $n $s1 {$s2} {$...}
#
# Used by many functions like strncmp to truncate arguments for comparison.
# Echoes the first n characters of each string s1 s2 ... on stdout.
#:end docstring:
###;;;autoload
function strtrunc ()
{
n=$1 ; shift
for z; do
echo "${z:0:$n}"
done
}
# provide string
# string.bash ends here
# ========================================================================== #
# ==> Everything below here added by the document author.
# ==> Suggested use of this script is to delete everything below here,
# ==> and "source" this file into your own scripts.
# strcat
string0=one
string1=two
echo
echo "Testing \"strcat\" function:"
echo "Original \"string0\" = $string0"
echo "\"string1\" = $string1"
strcat string0 string1
echo "New \"string0\" = $string0"
echo
# strlen
echo
echo "Testing \"strlen\" function:"
str=123456789
echo "\"str\" = $str"
echo -n "Length of \"str\" = "
strlen str
echo
# Exercise:
# --------
# Add code to test all the other string functions above.
exit 0 |
Stephane Chazelas demonstrates object-oriented programming in a
Bash script. Example A-20. Object-oriented database #!/bin/bash
# obj-oriented.sh: Object-oriented programming in a shell script.
# Script by Stephane Chazelas.
person.new() # Looks almost like a class declaration in C++.
{
local obj_name=$1 name=$2 firstname=$3 birthdate=$4
eval "$obj_name.set_name() {
eval \"$obj_name.get_name() {
echo \$1
}\"
}"
eval "$obj_name.set_firstname() {
eval \"$obj_name.get_firstname() {
echo \$1
}\"
}"
eval "$obj_name.set_birthdate() {
eval \"$obj_name.get_birthdate() {
echo \$1
}\"
eval \"$obj_name.show_birthdate() {
echo \$(date -d \"1/1/1970 0:0:\$1 GMT\")
}\"
eval \"$obj_name.get_age() {
echo \$(( (\$(date +%s) - \$1) / 3600 / 24 / 365 ))
}\"
}"
$obj_name.set_name $name
$obj_name.set_firstname $firstname
$obj_name.set_birthdate $birthdate
}
echo
person.new self Bozeman Bozo 101272413
# Create an instance of "person.new" (actually passing args to the function).
self.get_firstname # Bozo
self.get_name # Bozeman
self.get_age # 28
self.get_birthdate # 101272413
self.show_birthdate # Sat Mar 17 20:13:33 MST 1973
echo
# typeset -f
# to see the created functions (careful, it scrolls off the page).
exit 0 |
|
