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Unix Shell Scripts

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that file is called shell script language. Like other programming languages it has variables and flow control. statements (e.g. ifthenelse while for ...

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Unix Shell ScriptsPage 1Unix Shell ScriptsNorman MatloffJuly 15 2002Contents1 Introduction12 Invoking Shell Scripts22.1 Direct Interpretation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22.2 Indirect Interpretation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .23 Shell Variables33.1 Setting Variables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .33.2 Referencing and Testing Shell Variables . . . . . . . . . . . . . . . . . . . . . . . . . . . .34 Command Arguments45 Language Constructs56 Examples76.1 A Shell Script For Deleting Files . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .77 Further Information81 IntroductionIn previous discussions we have talked about many of the facilities of the C shell such as command aliasingjob control etc. In addition any collection of csh commands may be stored in a file and csh can be invokedto execute the commands in that file. Such a file is known as a shell script file. The language used in1Page 2that file is called shell script language. Like other programming languages it has variables and flow controlstatements (e.g. ifthenelse while for goto).In Unix there are several shells that can be used the C shell (csh and its extension the T C shell tcsh) theBourne Shell (sh and its extensions the Bourne Again Shell bash and the highly programmable Korn shellksh ) being the more commonly used.Note that you can run any shell simply by typing its name. For example if I am now running csh and wishto switch to ksh I simply type ksh and a Korn shell will start up for me. All my commands from that pointon will be read and processed by the Korn shell (though when I eventually want to log off exiting the Kornshell will still leave me in the C shell so I will have to exit from it too).2 Invoking Shell ScriptsThere are two ways to invoke a shell script file.2.1 Direct InterpretationIn direct interpretation the commandcsh filename arg .. ...

Source: heather.cs.ucdavis.edu

 

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