mirror of
https://github.com/u-boot/u-boot.git
synced 2025-04-17 18:34:42 +00:00
a9122d2c45
Provide a man-page for the if command. Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
72 lines
1.4 KiB
ReStructuredText
72 lines
1.4 KiB
ReStructuredText
.. SPDX-License-Identifier: GPL-2.0-or-later
|
|
|
|
.. index::
|
|
single: if (command)
|
|
|
|
if command
|
|
==========
|
|
|
|
Synopsis
|
|
--------
|
|
|
|
::
|
|
|
|
if <test statement>
|
|
then
|
|
<statements>
|
|
fi
|
|
|
|
if <test statement>
|
|
then
|
|
<statements>
|
|
else
|
|
<statements>
|
|
fi
|
|
|
|
Description
|
|
-----------
|
|
|
|
The if command is used to conditionally execute statements.
|
|
|
|
test statement
|
|
Any command. The test statement set the $? variable. If the value of
|
|
$? becomes 0 (true) the statements after the **then** statement will
|
|
be executed. Otherwise the statements after the **else** statement.
|
|
|
|
Example
|
|
-------
|
|
|
|
The examples shows how the value of a numeric variable can be tested with
|
|
**itest**.
|
|
|
|
::
|
|
|
|
=> a=1; if itest $a == 0; then echo true; else echo false; fi
|
|
false
|
|
=> a=0; if itest $a == 0; then echo true; else echo false; fi
|
|
true
|
|
|
|
In the following example we try to load an EFI binary via TFTP. If loading
|
|
succeeds, the binary is executed.
|
|
|
|
::
|
|
|
|
if tftp $kernel_addr_r shellriscv64.efi; then bootefi $kernel_addr_r; fi
|
|
|
|
Return value
|
|
------------
|
|
|
|
The value of $? is the return value of the last executed statement.
|
|
|
|
::
|
|
|
|
=> if true; then true; else true; fi; echo $?
|
|
0
|
|
=> if false; then true; else true; fi; echo $?
|
|
0
|
|
=> if false; then false; else false; fi; echo $?
|
|
1
|
|
=> if true; then false; else false; fi; echo $?
|
|
1
|
|
=> if false; then true; fi; echo $?
|
|
1
|