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>Typing variables: declare or
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>Advanced Bash-Scripting Guide: An in-depth exploration of the art of shell scripting</TH
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HREF="variables2.html"
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>Chapter 9. Another Look at Variables</TD
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>9.2. Typing variables: <B
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HREF="internal.html#BUILTINREF"
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>, which are exact synonyms,
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permit modifying the properties of variables. This is
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a very weak form of the <I
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available in certain programming languages. The
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> command is specific to version
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2 or later of Bash. The <I
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also works in ksh scripts.</P
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NAME="DECLAREOPSREF1"
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>declare/typeset options</B
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>This is the rough equivalent of the <B
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> type qualifier. An attempt
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to change the value of a <I
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variable fails with an error message.</P
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CLASS="PROGRAMLISTING"
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> 1 declare -r var1=1
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2 echo "var1 = $var1" # var1 = 1
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4 (( var1++ )) # x.sh: line 4: var1: readonly variable</PRE
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CLASS="PROGRAMLISTING"
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> 1 declare -i number
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2 # The script will treat subsequent occurrences of "number" as an integer.
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5 echo "Number = $number" # Number = 3
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8 echo "Number = $number" # Number = 0
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9 # Tries to evaluate the string "three" as an integer.</PRE
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>Certain arithmetic operations are permitted
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for declared integer variables without the need
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HREF="moreadv.html#EXPRREF"
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HREF="internal.html#LETREF"
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CLASS="PROGRAMLISTING"
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2 echo "n = $n" # n = 6/3
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6 echo "n = $n" # n = 2</PRE
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CLASS="PROGRAMLISTING"
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> 1 declare -a indices</PRE
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HREF="arrays.html#ARRAYREF"
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> 1 declare -f</PRE
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arguments in a script causes a listing of all the
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HREF="functions.html#FUNCTIONREF"
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defined in that script.</P
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CLASS="PROGRAMLISTING"
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> 1 declare -f function_name</PRE
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>declare -f function_name</B
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in a script lists just the function named.</P
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HREF="internal.html#EXPORTREF"
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CLASS="PROGRAMLISTING"
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> 1 declare -x var3</PRE
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>This declares a variable as available for exporting outside the
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environment of the script itself.</P
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> 1 declare -x var3=373</PRE
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assigning a value to a variable in the same statement
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as setting its properties.</P
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>Example 9-10. Using <I
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> to type variables</B
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CLASS="PROGRAMLISTING"
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5 echo This is a function.
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8 declare -f # Lists the function above.
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12 declare -i var1 # var1 is an integer.
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14 echo "var1 declared as $var1"
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15 var1=var1+1 # Integer declaration eliminates the need for 'let'.
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16 echo "var1 incremented by 1 is $var1."
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17 # Attempt to change variable declared as integer.
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18 echo "Attempting to change var1 to floating point value, 2367.1."
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19 var1=2367.1 # Results in error message, with no change to variable.
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20 echo "var1 is still $var1"
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24 declare -r var2=13.36 # 'declare' permits setting a variable property
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25 #+ and simultaneously assigning it a value.
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26 echo "var2 declared as $var2" # Attempt to change readonly variable.
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27 var2=13.37 # Generates error message, and exit from script.
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29 echo "var2 is still $var2" # This line will not execute.
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31 exit 0 # Script will not exit here.</PRE
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HREF="subshells.html#SCOPEREF"
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CLASS="PROGRAMLISTING"
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12 bar # Prints bar.</PRE
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CLASS="PROGRAMLISTING"
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2 declare FOO="bar"
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11 bar # Prints nothing.
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14 # Thank you, Michael Iatrou, for pointing this out.</PRE
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>9.2.1. Another use for <I
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helpful in identifying variables, <A
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HREF="othertypesv.html#ENVREF"
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This can be especially useful with <A
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HREF="arrays.html#ARRAYREF"
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>declare | grep HOME</B
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CLASS="COMPUTEROUTPUT"
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>declare | grep zzy</B
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CLASS="COMPUTEROUTPUT"
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>Colors=([0]="purple" [1]="reddish-orange" [2]="light green")</B
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>echo ${Colors[@]}</B
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CLASS="COMPUTEROUTPUT"
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>purple reddish-orange light green</TT
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>declare | grep Colors</B
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>Colors=([0]="purple" [1]="reddish-orange" [2]="light green")</TT
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HREF="declareref.html#AEN5557"
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a variable means to classify it and restrict its properties.
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For example, a variable <I
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is no longer available for <A
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HREF="refcards.html#STRINGOPSTAB"
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CLASS="PROGRAMLISTING"
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> 1 declare -i intvar
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4 echo "$intvar" # 23
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5 intvar=stringval
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6 echo "$intvar" # 0</PRE
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HREF="variables2.html"
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>Another Look at Variables</TD
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HREF="variables2.html"
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>$RANDOM: generate random integer</TD
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