Advanced Bash−Scripting Guide

Advanced Bash−Scripting Guide
# Thank you, S.C.
34.4. Recursion
Can a script recursively call itself? Indeed.
Example 34−6. A (useless) script that recursively calls itself
#!/bin/bash
# recurse.sh
# Can a script recursively call itself?
# Yes, but is this of any practical use?
# (See the following script.)
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.
# Explain why.
exit 0
Example 34−7. A (useful) script that recursively calls itself
#!/bin/bash
# pb.sh: phone book
# Written by Rick Boivie, and used with permission.
# Modifications by document author.
MINARGS=1 # Script needs at least one argument.
DATAFILE=./phonebook
PROGNAME=$0
E_NOARGS=70 # No arguments error.
if [ $# −lt $MINARGS ]; then
echo "Usage: "$PROGNAME" data"
exit $E_NOARGS
fi
if [ $# −eq $MINARGS ]; then
grep $1 "$DATAFILE"
else
Chapter 34. Miscellany 341