Advanced Bash−Scripting Guide

echo "However, the script may also contain shell and system commands."
exit 0
Advanced Bash−Scripting Guide
It is even possible to combine a Bash script and Perl script within the same file. Depending on how the script
is invoked, either the Bash part or the Perl part will execute.
Example 34−5. Bash and Perl scripts combined
#!/bin/bash
# bashandperl.sh
echo "Greetings from the Bash part of the script."
# More Bash commands may follow here.
exit 0
# End of Bash part of the script.
# =======================================================
#!/usr/bin/perl
# This part of the script must be invoked with −x option.
print "Greetings from the Perl part of the script.\n";
# More Perl commands may follow here.
# End of Perl part of the script.
bash$ bash bashandperl.sh
Greetings from the Bash part of the script.
bash$ perl −x bashandperl.sh
Greetings from the Perl part of the script.
34.3. Tests and Comparisons: Alternatives
For tests, the [[ ]] construct may be more appropriate than [ ]. Likewise, arithmetic comparisons might
benefit from the (( )) construct.
a=8
# All of the comparisons below are equivalent.
test "$a" −lt 16 && echo "yes, $a < 16"
# "and list"
/bin/test "$a" −lt 16 && echo "yes, $a < 16"
[ "$a" −lt 16 ] && echo "yes, $a < 16"
[[ $a −lt 16 ]] && echo "yes, $a < 16" # Quoting variables within
(( a < 16 )) && echo "yes, $a < 16" # [[ ]] and (( )) not necessary.
city="New York"
# Again, all of the comparisons below are equivalent.
test "$city" \< Paris && echo "Yes, Paris is greater than $city" # Greater ASCII order.
/bin/test "$city" \< Paris && echo "Yes, Paris is greater than $city"
[ "$city" \< Paris ] && echo "Yes, Paris is greater than $city"
[[ $city < Paris ]] && echo "Yes, Paris is greater than $city" # Need not quote $city.
Chapter 34. Miscellany 340