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→INVESTIGATION 3: USING CONTROL FLOW STATEMENTS IN SHELL SCRIPTS
# Issue a linux command to display the value of '''$?'''. What is the result? Why?<br><br>
# Issue the following linux command to test a condition involving numbers:<br><span style="color:blue;font-weight:bold;font-family:courier;">test $number1 > $number2</span><br><br>
# Issue a linux command to display the value of '''$?'''. '''NOTE: ''' You will notice that something is '''wrong'''.The exit status '''$?''' shows a zero (TRUE) value, but the number 5 is definitely NOT greater than 10. The problem is that the symbols '''<''' and '''>''' are interpreted as REDIRECTION symbols!<br><br># To prove this, issue the following linux command :<br><span style="color:blue;font-weight:bold;font-family:courier;">ls -1 5</span><br><br>You should notice an empty file called "'''5'''". The correctly issued test command used redirect to create an empty file instead, what succeeded just giving a TRUE value!<br><br>To prevent these incorrectly issued testing for number comparison, you can use the following options instead:<br>'''-lt''' (<), '''-le''' (<&equals), '''-gt''' (>), '''-ge''' (>'''NOTE:''' You will notice that something is '''wrong'''. The exit status '''$?''' shows a zero (TRUE) value, but the number 5 is definitely NOT greater than 10. The problem is that the symbols '''<''' and '''>''' are interpreted as REDIRECTION symbols!<br><br># To prove this, issue the following linux command :<br><span style="color:blue;font-weight:bold;font-family:courier;">ls -1 5</span><br><br>You should notice an empty file called "'''5'''". The correctly issued test command used redirect to create an empty file instead, what succeeded just giving a TRUE value!<br><br>To prevent these incorrectly issued testing for number comparison, you can use the following options instead:<br>'''-lt''' (<), '''-le''' (<=), '''-gt''' (>), '''-ge''' (>=), '''-eq''' (=), '''-ne''' (!=)<br><br># x), '''-eq''' ('''NOTE:''' You will notice that something is '''wrong'''. The exit status '''$?''' shows a zero (TRUE) value, but the number 5 is definitely NOT greater than 10. The problem is that the symbols '''<''' and '''>''' are interpreted as REDIRECTION symbols!<br><br># To prove this, issue the following linux command :<br><span style="color:blue;font-weight:bold;font-family:courier;">ls -1 5</span><br><br>You should notice an empty file called "'''5'''". The correctly issued test command used redirect to create an empty file instead, what succeeded just giving a TRUE value!<br><br>To prevent these incorrectly issued testing for number comparison, you can use the following options instead:<br>'''-lt''' (<), '''-le''' (<=), '''-gt''' (>), '''-ge''' (>=), '''-eq''' (=), '''-ne''' (!=)<br><br># x), '''-ne''' (!'''NOTE:''' You will notice that something is '''wrong'''. The exit status '''$?''' shows a zero (TRUE) value, but the number 5 is definitely NOT greater than 10. The problem is that the symbols '''<''' and '''>''' are interpreted as REDIRECTION symbols!<br><br># To prove this, issue the following linux command :<br><span style="color:blue;font-weight:bold;font-family:courier;">ls -1 5</span><br><br>You should notice an empty file called "'''5'''". The correctly issued test command used redirect to create an empty file instead, what succeeded just giving a TRUE value!<br><br>To prevent these incorrectly issued testing for number comparison, you can use the following options instead:<br>'''-lt''' (<), '''-le''' (<=), '''-gt''' (>), '''-ge''' (>=), '''-eq''' (=), '''-ne''' (!=)<br><br># x)<br><br># x
= LINUX PRACTICE QUESTIONS =
