Advanced Bash−Scripting Guide

Advanced Bash−Scripting Guide
v3=${v0/#123/000}
echo "v3 = $v3"
v4=${v0/%123/000}
echo "v4 = $v4"
# Matches, but not at beginning.
# abc1234zip1234abc
# NO REPLACEMENT.
# Matches, but not at end.
# abc1234zip1234abc
# NO REPLACEMENT.
exit 0
${!varprefix*}, ${!varprefix@}
Matches all previously declared variables beginning with varprefix.
xyz23=whatever
xyz24=
a=${!xyz*}
echo "a = $a"
a=${!xyz@}
echo "a = $a"
# Expands to names of declared variables beginning with "xyz".
# a = xyz23 xyz24
# Same as above.
# a = xyz23 xyz24
# Bash, version 2.04, adds this feature.
9.4. Typing variables: declare or typeset
The declare or typeset builtins (they are exact synonyms) permit restricting the properties of variables. This
is a very weak form of the typing available in certain programming languages. The declare command is
specific to version 2 or later of Bash. The typeset command also works in ksh scripts.
declare/typeset options
−r readonly
declare −r var1
(declare −r var1 works the same as readonly var1)
This is the rough equivalent of the C const type qualifier. An attempt to change the value of a
readonly variable fails with an error message.
−i integer
declare −i number
# The script will treat subsequent occurrences of "number" as an integer.
number=3
echo "number = $number" # number = 3
number=three
echo "number = $number" # number = 0
# Tries to evaluate "three" as an integer.
Note that certain arithmetic operations are permitted for declared integer variables without the need
for expr or let.
−a array
declare −a indices
Chapter 9. Variables Revisited 92