| 1 | #!/bin/sh
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| 2 |
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| 3 | # We used the if/else case but that is often not needed in shell. We can
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| 4 | # instead use && and || for many cases. Take a look at the snippet below
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| 5 | #
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| 6 | # $ sh foo.sh && sh bar.sh
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| 7 | #
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| 8 | # The snippet above means that if 'sh foo.sh' is ran successfully,
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| 9 | # without error, then 'sh bas.sh' will be ran.
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| 10 | #
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| 11 | # $ sh foo.sh || sh bar.sh
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| 12 | #
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| 13 | # If 'sh foo.sh' is ran and an error does occur, then 'sh bar.sh' is
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| 14 | # ran.
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| 15 | #
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| 16 | # Some conditions require square brackets, these are test expressions.
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| 17 | # Examples of conditions that require square brackets are usually string
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| 18 | # and string comparisons, existence of files, and empty or not files.
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| 19 | #
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| 20 | # $ mv file1 file2 || echo "Could not be moved"
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| 21 | # $ [ -z "$1" ] || echo "Nothing was entered"
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| 22 | #
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| 23 | # You can also extend it
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| 24 | #
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| 25 | # $ [ "$1" = "password123" ] || { echo "power off"; sh shutdown.sh; }
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| 26 | #
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| 27 | # The semi colon is used the same way as other programming languages
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| 28 | # where you can combine multiple lines into a single line. Note that
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| 29 | # it should still be easily readable to humans to debug and understand.
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| 30 | # If you go back to exercise 14, you can see them being used to condense
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| 31 | # the 'do' word
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| 32 | #
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| 33 | # Fix the code below so the echo commands make sense with the pin 1412
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| 34 | # Leave the two && in place
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| 35 |
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| 36 | [] && echo "incorrect pin"
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| 37 | [] && echo "correct pin"
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| 38 |
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| 39 | # You can also combine it into 1 line but it doesn't always comply with
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| 40 | # many shells
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| 41 | #
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| 42 | # $ [] && echo "good" || echo "bad"
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