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d2fbe1fa29
Add a cross reference to the itest command. Fix a typo: %s/Example/Examples/. Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
73 lines
1.4 KiB
ReStructuredText
73 lines
1.4 KiB
ReStructuredText
.. SPDX-License-Identifier: GPL-2.0-or-later
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.. index::
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single: if (command)
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if command
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==========
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Synopsis
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--------
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::
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if <test statement>
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then
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<statements>
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fi
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if <test statement>
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then
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<statements>
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else
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<statements>
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fi
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Description
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-----------
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The if command is used to conditionally execute statements.
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test statement
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Any command. The test statement set the $? variable. If the value of
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$? becomes 0 (true) the statements after the **then** statement will
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be executed. Otherwise the statements after the **else** statement.
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Examples
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--------
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The examples shows how the value of a numeric variable can be tested with
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the :doc:`itest <itest>` command.
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::
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=> a=1; if itest $a == 0; then echo true; else echo false; fi
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false
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=> a=0; if itest $a == 0; then echo true; else echo false; fi
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true
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In the following example we try to load an EFI binary via TFTP. If loading
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succeeds, the binary is executed.
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::
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if tftp $kernel_addr_r shellriscv64.efi; then bootefi $kernel_addr_r; fi
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Return value
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------------
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The value of $? is the return value of the last executed statement.
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::
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=> if true; then true; else true; fi; echo $?
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0
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=> if false; then true; else true; fi; echo $?
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0
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=> if false; then false; else false; fi; echo $?
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1
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=> if true; then false; else false; fi; echo $?
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1
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=> if false; then true; fi; echo $?
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1
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