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OPS235 Lab 1 - CentOS7 - VMware

17 bytes removed, 07:39, 22 May 2016
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{{Admon/note|Bash Shell Reference Guide:|<br>'''<u>She-bang Line</u>'''<ul><li>Forces shell script to run in a specific Shell</li><li>Some shell syntax not backward compatible</li><li>'''#!''' must be at beginning of first line of shell script</li><li>Example: '''#!/bin/bash'''<br><br></li></ul>'''<u>Variables</u>'''<br><br>'''Environment'''<ul><li>System-wide or "global" variable (usually UPPERCASE)</li><li>Can view with command: '''set &#124; more'''</li><li>'''$''' in front to expand variable to value<li>Examples: '''USER''', '''PATH''', '''HOME''', '''SHELL'''<br><br></li></ul> '''User-defined''' <ul><li>Variable created by user (command line, scripting)</li><li>'''Examples:'''<br>'''myVar&#61;"my value"'''; '''readonly myVar'''; export myVar<br>'''read -p "enter value: " myVar'''<br><br></li></ul>'''positional Positional parameters'''<ul><li> Assign values with set command or shell script arguments</li><li>These variables are numbered (eg. $1, $2... containing arguments after shell script or by using set command (eg. '''set $(ls)''' ). Using dollar sign ('''10}</li><li>Special parameters: $*, $@, $#, $$, $''') in front of variable expands the value assigned.?<br><br></li><li/ul>''''''Command Substitution:''''''<brul><brli>A very useful trick Useful method to take expand output from a command to be used as an argument for another command. </li><li>Examples include:<br>'''file $(ls)'''<br>'''set $(ls);echo $#;echo $*'''<br>'''echo "hostname: $(hostname)"'''<br><br><li>'''Logic Control Flow Statements:'''<br><br>The '''test''' command can be used to see if a condition is true or false<br>(i.e. test $USER &#61; "root") . The '''$?''' special shell variable stores the result (zero if true, non-zero if false). Square brackets '''[ ]''' can be used to represent the test command with the condition <u>inside</u> the brackets (spaces separating brackets).Can use '''if''' / '''if-else''' / '''if-elif-else''' statements with brackets. The '''exit''' command can be used to terminate the shell script with a false value.<br><br>'''<u>Examples</u>'''<br><br>''if [ $USER &#61; "root" ]''<br>''then''<br>&nbsp;''echo "You must be root" >&amp;2''<br>&nbsp;''exit1''<br>''fi''<br><br># For number comparison: use:<br># -gt,-ge, -lt, -le, -eq, -ne<br><br>''if [ $age -gt 65 ]''<br>''then''<br>&nbsp;''echo "retire"''<br>''else''<br>&nbsp;''echo "don't retire"''<br>''fi''<br><br>''if [ $grade -gt 79 ]''<br>''then''<br>&nbsp;''echo "You get Good Mark"''<br>''elif [ $grade -gt 49 ]''<br>''then''<br>&nbsp;''echo "You pass"''<br>''else''<br>&nbsp;''echo "You fail"''<br>''fi''<br></li></ul>}}
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