Advanced Bash−Scripting Guide

Advanced Bash−Scripting Guide
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@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 :−) )
#
# ==> '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.
Appendix A. Contributed Scripts 390