mirror of https://github.com/tLDP/LDP
41 lines
1.3 KiB
Bash
41 lines
1.3 KiB
Bash
#!/bin/bash
|
|
# self-source.sh: a script sourcing itself "recursively."
|
|
# From "Stupid Script Tricks," Volume II.
|
|
|
|
MAXPASSCNT=100 # Maximum number of execution passes.
|
|
|
|
echo -n "$pass_count "
|
|
# At first execution pass, this just echoes two blank spaces,
|
|
#+ since $pass_count still uninitialized.
|
|
|
|
let "pass_count += 1"
|
|
# Assumes the uninitialized variable $pass_count
|
|
#+ can be incremented the first time around.
|
|
# This works with Bash and pdksh, but
|
|
#+ it relies on non-portable (and possibly dangerous) behavior.
|
|
# Better would be to initialize $pass_count to 0 before incrementing.
|
|
|
|
while [ "$pass_count" -le $MAXPASSCNT ]
|
|
do
|
|
. $0 # Script "sources" itself, rather than calling itself.
|
|
# ./$0 (which would be true recursion) doesn't work here. Why?
|
|
done
|
|
|
|
# What occurs here is not actually recursion,
|
|
#+ since the script effectively "expands" itself, i.e.,
|
|
#+ generates a new section of code
|
|
#+ with each pass through the 'while' loop',
|
|
# with each 'source' in line 20.
|
|
#
|
|
# Of course, the script interprets each newly 'sourced' "#!" line
|
|
#+ as a comment, and not as the start of a new script.
|
|
|
|
echo
|
|
|
|
exit 0 # The net effect is counting from 1 to 100.
|
|
# Very impressive.
|
|
|
|
# Exercise:
|
|
# --------
|
|
# Write a script that uses this trick to actually do something useful.
|