Advanced Bash−Scripting Guide

echo "one two three" | read a b c
# Try to reassign a, b, and c.
echo
echo "a = $a" # a = aaa
echo "b = $b" # b = bbb
echo "c = $c" # c = ccc
# Reassignment failed.
# −−−−−−−−−−−−−−−−−−−−−−−−−−−−−−
# Try the following alternative.
var=`echo "one two three"`
set −− $var
a=$1; b=$2; c=$3
echo "−−−−−−−"
echo "a = $a" # a = one
echo "b = $b" # b = two
echo "c = $c" # c = three
# Reassignment succeeded.
# −−−−−−−−−−−−−−−−−−−−−−−−−−−−−−
Advanced Bash−Scripting Guide
# Note also that an echo to a 'read' works within a subshell.
# However, the value of the variable changes *only* within the subshell.
a=aaa
b=bbb
c=ccc
# Starting all over again.
echo; echo
echo "one two three" | ( read a b c;
echo "Inside subshell: "; echo "a = $a"; echo "b = $b"; echo "c = $c" )
# a = one
# b = two
# c = three
echo "−−−−−−−−−−−−−−−−−"
echo "Outside subshell: "
echo "a = $a" # a = aaa
echo "b = $b" # b = bbb
echo "c = $c" # c = ccc
echo
exit 0
Using "suid" commands within scripts is risky, as it may compromise system security. [62]
Using shell scripts for CGI programming may be problematic. Shell script variables are not "typesafe", and
this can cause undesirable behavior as far as CGI is concerned. Moreover, it is difficult to "cracker−proof"
shell scripts.
Bash does not handle the double slash (//) string correctly.
Bash scripts written for Linux or BSD systems may need fixups to run on a commercial UNIX machine. Such
scripts often employ GNU commands and filters which have greater functionality than their generic UNIX
counterparts. This is particularly true of such text processing utilites as tr.
Chapter 32. Gotchas 331