224 lines
3.5 KiB
HTML
224 lines
3.5 KiB
HTML
<HTML
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><HEAD
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><TITLE
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>Variables</TITLE
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>Bash Prompt HOWTO: </TH
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>Prev</A
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>Chapter 3. Bash Programming and Shell Scripts</TD
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><H1
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><A
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NAME="AEN191"
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></A
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>3.1. Variables</H1
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><P
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>I'm not going to try to explain all the details of Bash scripting in a
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section of this HOWTO, just the details pertaining to prompts. If you want
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to know more about shell programming and Bash in general, I highly
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recommend <EM
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>Learning the Bash Shell</EM
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> by Cameron Newham
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and Bill Rosenblatt (O'Reilly, 1998). Oddly, my copy of this book is quite
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frayed. Again, I'm going to assume that you know a fair bit about Bash
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already. You can skip this section if you're only looking for the basics,
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but remember it and refer back if you proceed much farther. </P
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><P
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>Variables in Bash are assigned much as they are in any programming
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language:</P
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><TABLE
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BORDER="1"
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BGCOLOR="#E0E0E0"
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WIDTH="100%"
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><TR
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><TD
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><FONT
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COLOR="#000000"
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><PRE
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CLASS="SCREEN"
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>testvar=5
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foo=zen
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bar="bash prompt"</PRE
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></FONT
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></TD
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></TR
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></TABLE
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><P
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>Quotes are only needed in an assignment if a space (or special character,
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discussed shortly) is a part of the variable.</P
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><P
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>Variables are referenced slightly differently than they are assigned:</P
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><TABLE
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BORDER="1"
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BGCOLOR="#E0E0E0"
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WIDTH="100%"
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><TR
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><TD
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><FONT
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COLOR="#000000"
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><PRE
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CLASS="SCREEN"
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>> echo $testvar
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5
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> echo $foo
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zen
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> echo ${bar}
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bash prompt
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> echo $NotAssigned
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> </PRE
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></FONT
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></TD
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></TR
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></TABLE
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><P
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>A variable can be referred to as <TT
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CLASS="VARNAME"
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>$bar</TT
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> or
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<TT
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CLASS="VARNAME"
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>${bar}</TT
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>. The braces are useful when it is unclear what
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is being referenced: if I write <TT
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CLASS="VARNAME"
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>$barley</TT
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> do I mean
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<TT
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CLASS="VARNAME"
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>${bar}ley</TT
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> or <TT
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CLASS="VARNAME"
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>${barley}</TT
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>? Note also
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that referencing a value that hasn't been assigned doesn't generate an
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error, instead returning nothing. </P
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>Bash Programming and Shell Scripts</TD
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> |