Unix Shells By Example 4th Edition Pdf
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Some Unix commands take one or more arguments, which provide a way to refine the utility's behavior. For example, a user might enter the command rm OldFIle.txt. The command is calling the rm utility, which deletes files in a directory. The command also includes the argument OldFIle.txt, which is the file to be deleted. When the user enters this command in the shell, the kernel runs the rm program and deletes the specified file.
Unix supports multiple shells, including sh, csh, ksh, tcsh and bash. A Unix distribution typically designates a default shell, but users can choose from any of the supported shells. Users can also customize the shell environment, or they can write their own shell scripts.
6. Escape CharactersCertain characters are significant to the shell; we have seen, for example,that the use of double quotes (\") characters affect how spaces andTAB characters are treated, for example:if(typeof ez_ad_units!='undefined'){ez_ad_units.push([[728,90],'shellscript_sh-box-3','ezslot_6',135,'0','0'])};__ez_fad_position('div-gpt-ad-shellscript_sh-box-3-0');$ echo Hello WorldHello World$ echo \"Hello World\"Hello WorldSo how do we display: Hello \"World\" $ echo \"Hello \\\"World\\\"\"The first and last \" characters wrap the whole lot into one parameterpassed to echo so that the spacing between the two words iskept as is. But the code:if(typeof ez_ad_units!='undefined'){ez_ad_units.push([[728,90],'shellscript_sh-medrectangle-3','ezslot_2',133,'0','0'])};__ez_fad_position('div-gpt-ad-shellscript_sh-medrectangle-3-0');$ echo \"Hello \" World \"\"would be interpreted as three parameters:if(typeof ez_ad_units!='undefined'){ez_ad_units.push([[300,250],'shellscript_sh-banner-1','ezslot_7',143,'0','0'])};__ez_fad_position('div-gpt-ad-shellscript_sh-banner-1-0');if(typeof ez_ad_units!='undefined'){ez_ad_units.push([[300,250],'shellscript_sh-banner-1','ezslot_8',143,'0','1'])};__ez_fad_position('div-gpt-ad-shellscript_sh-banner-1-0_1');if(typeof ez_ad_units!='undefined'){ez_ad_units.push([[300,250],'shellscript_sh-banner-1','ezslot_9',143,'0','2'])};__ez_fad_position('div-gpt-ad-shellscript_sh-banner-1-0_2');.banner-1-multi-143{border:none!important;display:block!important;float:none!important;line-height:0;margin-bottom:15px!important;margin-left:auto!important;margin-right:auto!important;margin-top:15px!important;max-width:100%!important;min-height:250px;min-width:300px;padding:0;text-align:center!important}\"Hello \"World\"\"So the output would beif(typeof ez_ad_units!='undefined'){ez_ad_units.push([[300,250],'shellscript_sh-medrectangle-4','ezslot_4',134,'0','0'])};__ez_fad_position('div-gpt-ad-shellscript_sh-medrectangle-4-0');Hello WorldNote that we lose the quotes entirely. This is because the first and second quotes mark offthe Hello and following spaces; the second argument is an unquoted \"World\" and the third argument is the empty string; \"\".Thanks to Patrick for pointing out that this:if(typeof ez_ad_units!='undefined'){ez_ad_units.push([[970,90],'shellscript_sh-box-4','ezslot_1',120,'0','0'])};__ez_fad_position('div-gpt-ad-shellscript_sh-box-4-0');$ echo \"Hello \"World\"\"is actually only one parameter (no spaces between the quoted parameters), and that you can test this by replacing the echo command with (for example) ls.Most characters (*, ', etc) are not interpreted (ie, they aretaken literally) by means of placing them in double quotes (\"\"). They are takenas is and passed on to the command being called. An example using the asterisk (*) goes:$ echo *case.shtml escape.shtml first.shtml functions.shtml hints.shtml index.shtml ip-primer.txt raid1+0.txt$ echo *txtip-primer.txt raid1+0.txt$ echo \"*\"*$ echo \"*txt\"*txtIn the first example, * is expanded to mean all files in the current directory.In the second example, *txt means all files ending in txt.In the third, we put the * in double quotes, and it is interpreted literally.In the fourth example, the same applies, but we have appended txt to the string.However, \", $, `, and \\ are still interpreted bythe shell, even when they're in double quotes.The backslash (\\) character is used to mark these special characters so thatthey are not interpreted by the shell, but passed on to the command being run(for example, echo).So to output the string: (Assuming that the value of $X is 5):if(typeof ez_ad_units!='undefined'){ez_ad_units.push([[250,250],'shellscript_sh-large-leaderboard-2','ezslot_3',122,'0','0'])};__ez_fad_position('div-gpt-ad-shellscript_sh-large-leaderboard-2-0');A quote is \", backslash is \\, backtick is `.A few spaces are and dollar is $. $X is 5.we would have to write:$ echo \"A quote is \\\", backslash is \\\\, backtick is \\`.\"A quote is \", backslash is \\, backtick is `.$ echo \"A few spaces are and dollar is \\$. \\$X is ${X}.\"A few spaces are and dollar is $. $X is 5.We have seen why the \" is special for preserving spacing. Dollar ($) isspecial because it marks a variable, so $X isreplaced by the shell with the contents of the variable X.Backslash (\\) is special because it is itself used to mark other charactersoff; we need the following options for a complete shell:if(typeof ez_ad_units!='undefined'){ez_ad_units.push([[300,250],'shellscript_sh-leader-1','ezslot_5',123,'0','0'])};__ez_fad_position('div-gpt-ad-shellscript_sh-leader-1-0');$ echo \"This is \\\\ a backslash\"This is \\ a backslash$ echo \"This is \\\" a quote and this is \\\\ a backslash\"This is \" a quote and this is \\ a backslashSo backslash itself must be escaped to show that it is to be taken literally.The other special character, the backtick, is discussed later in Chapter 12, External Programs.
You can mail me with this form. If you expect a reply, please ensure that the address you specify is valid. Don't forget to include the simple addition question at the end of the form, to prove that you are a real person!You can buy the content of this Shell Scripting Tutorial as a PDF!if(typeof ez_ad_units!='undefined'){ez_ad_units.push([[970,250],'shellscript_sh-medrectangle-1','ezslot_11',280,'0','0'])};__ez_fad_position('div-gpt-ad-shellscript_sh-medrectangle-1-0');report this adLoading...Copyright 2000 - 2022 Steve Parker
The following table shows the default UNIX system prompt and superuser prompt forshells that are included in the Oracle Solaris OS. Note that thedefault system prompt that is displayed in command examples varies, depending onthe Oracle Solaris release. 1e1e36bf2d