diff options
author | Scott Rifenbark <srifenbark@gmail.com> | 2018-02-01 10:30:31 -0800 |
---|---|---|
committer | Richard Purdie <richard.purdie@linuxfoundation.org> | 2018-02-14 15:25:31 +0000 |
commit | 8d320536dcda978a43693e1874c32d9d95e42b5e (patch) | |
tree | 4a92d9ea3daebc99c22b233cdf4ab1491655fc79 /documentation | |
parent | 72be05b9f5918a944db988da5e81c4833be37020 (diff) | |
download | poky-8d320536dcda978a43693e1874c32d9d95e42b5e.tar.gz |
dev-manual, getting-started: Moved the BB syntax section
This section on BitBake syntax appeared in the Getting Started
manual. I decided that it should live with the section on
writing a new recipe.
(From yocto-docs rev: 8d83ce3e11405b2f12f27cdd117a19c4af52146a)
Signed-off-by: Scott Rifenbark <srifenbark@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
Diffstat (limited to 'documentation')
-rw-r--r-- | documentation/dev-manual/dev-manual-common-tasks.xml | 328 | ||||
-rw-r--r-- | documentation/getting-started/getting-started-development-environment.xml | 299 |
2 files changed, 327 insertions, 300 deletions
diff --git a/documentation/dev-manual/dev-manual-common-tasks.xml b/documentation/dev-manual/dev-manual-common-tasks.xml index 167d107155..dbbe67657d 100644 --- a/documentation/dev-manual/dev-manual-common-tasks.xml +++ b/documentation/dev-manual/dev-manual-common-tasks.xml | |||
@@ -1507,8 +1507,8 @@ | |||
1507 | </itemizedlist> | 1507 | </itemizedlist> |
1508 | <note> | 1508 | <note> |
1509 | For information on recipe syntax, see the | 1509 | For information on recipe syntax, see the |
1510 | "<ulink url='&YOCTO_DOCS_GS_URL;#recipe-syntax'>Recipe Syntax</ulink>" | 1510 | "<link linkend='recipe-syntax'>Recipe Syntax</link>" |
1511 | section in the Getting Started With Yocto Project Manual. | 1511 | section. |
1512 | </note> | 1512 | </note> |
1513 | </para> | 1513 | </para> |
1514 | 1514 | ||
@@ -3505,6 +3505,330 @@ | |||
3505 | style. | 3505 | style. |
3506 | </para> | 3506 | </para> |
3507 | </section> | 3507 | </section> |
3508 | |||
3509 | <section id='recipe-syntax'> | ||
3510 | <title>Recipe Syntax</title> | ||
3511 | |||
3512 | <para> | ||
3513 | Understanding recipe file syntax is important for writing | ||
3514 | recipes. | ||
3515 | The following list overviews the basic items that make up a | ||
3516 | BitBake recipe file. | ||
3517 | For more complete BitBake syntax descriptions, see the | ||
3518 | "<ulink url='&YOCTO_DOCS_BB_URL;#bitbake-user-manual-metadata'>Syntax and Operators</ulink>" | ||
3519 | chapter of the BitBake User Manual. | ||
3520 | <itemizedlist> | ||
3521 | <listitem><para> | ||
3522 | <emphasis>Variable Assignments and Manipulations:</emphasis> | ||
3523 | Variable assignments allow a value to be assigned to a | ||
3524 | variable. | ||
3525 | The assignment can be static text or might include | ||
3526 | the contents of other variables. | ||
3527 | In addition to the assignment, appending and prepending | ||
3528 | operations are also supported.</para> | ||
3529 | |||
3530 | <para>The following example shows some of the ways | ||
3531 | you can use variables in recipes: | ||
3532 | <literallayout class='monospaced'> | ||
3533 | S = "${WORKDIR}/postfix-${PV}" | ||
3534 | CFLAGS += "-DNO_ASM" | ||
3535 | SRC_URI_append = " file://fixup.patch" | ||
3536 | </literallayout> | ||
3537 | </para></listitem> | ||
3538 | <listitem><para> | ||
3539 | <emphasis>Functions:</emphasis> | ||
3540 | Functions provide a series of actions to be performed. | ||
3541 | You usually use functions to override the default | ||
3542 | implementation of a task function or to complement | ||
3543 | a default function (i.e. append or prepend to an | ||
3544 | existing function). | ||
3545 | Standard functions use <filename>sh</filename> shell | ||
3546 | syntax, although access to OpenEmbedded variables and | ||
3547 | internal methods are also available.</para> | ||
3548 | |||
3549 | <para>The following is an example function from the | ||
3550 | <filename>sed</filename> recipe: | ||
3551 | <literallayout class='monospaced'> | ||
3552 | do_install () { | ||
3553 | autotools_do_install | ||
3554 | install -d ${D}${base_bindir} | ||
3555 | mv ${D}${bindir}/sed ${D}${base_bindir}/sed | ||
3556 | rmdir ${D}${bindir}/ | ||
3557 | } | ||
3558 | </literallayout> | ||
3559 | It is also possible to implement new functions that | ||
3560 | are called between existing tasks as long as the | ||
3561 | new functions are not replacing or complementing the | ||
3562 | default functions. | ||
3563 | You can implement functions in Python | ||
3564 | instead of shell. | ||
3565 | Both of these options are not seen in the majority of | ||
3566 | recipes. | ||
3567 | </para></listitem> | ||
3568 | <listitem><para><emphasis>Keywords:</emphasis> | ||
3569 | BitBake recipes use only a few keywords. | ||
3570 | You use keywords to include common | ||
3571 | functions (<filename>inherit</filename>), load parts | ||
3572 | of a recipe from other files | ||
3573 | (<filename>include</filename> and | ||
3574 | <filename>require</filename>) and export variables | ||
3575 | to the environment (<filename>export</filename>). | ||
3576 | </para> | ||
3577 | |||
3578 | <para>The following example shows the use of some of | ||
3579 | these keywords: | ||
3580 | <literallayout class='monospaced'> | ||
3581 | export POSTCONF = "${STAGING_BINDIR}/postconf" | ||
3582 | inherit autoconf | ||
3583 | require otherfile.inc | ||
3584 | </literallayout> | ||
3585 | </para></listitem> | ||
3586 | <listitem><para> | ||
3587 | <emphasis>Comments (#):</emphasis> | ||
3588 | Any lines that begin with the hash character | ||
3589 | (<filename>#</filename>) are treated as comment lines | ||
3590 | and are ignored: | ||
3591 | <literallayout class='monospaced'> | ||
3592 | # This is a comment | ||
3593 | </literallayout> | ||
3594 | </para></listitem> | ||
3595 | </itemizedlist> | ||
3596 | </para> | ||
3597 | |||
3598 | <para> | ||
3599 | This next list summarizes the most important and most commonly | ||
3600 | used parts of the recipe syntax. | ||
3601 | For more information on these parts of the syntax, you can | ||
3602 | reference the | ||
3603 | <ulink url='&YOCTO_DOCS_BB_URL;#bitbake-user-manual-metadata'>Syntax and Operators</ulink> | ||
3604 | chapter in the BitBake User Manual. | ||
3605 | <itemizedlist> | ||
3606 | <listitem><para> | ||
3607 | <emphasis>Line Continuation (\):</emphasis> | ||
3608 | Use the backward slash (<filename>\</filename>) | ||
3609 | character to split a statement over multiple lines. | ||
3610 | Place the slash character at the end of the line that | ||
3611 | is to be continued on the next line: | ||
3612 | <literallayout class='monospaced'> | ||
3613 | VAR = "A really long \ | ||
3614 | line" | ||
3615 | </literallayout> | ||
3616 | <note> | ||
3617 | You cannot have any characters including spaces | ||
3618 | or tabs after the slash character. | ||
3619 | </note> | ||
3620 | </para></listitem> | ||
3621 | <listitem><para> | ||
3622 | <emphasis>Using Variables (${<replaceable>VARNAME</replaceable>}):</emphasis> | ||
3623 | Use the <filename>${<replaceable>VARNAME</replaceable>}</filename> | ||
3624 | syntax to access the contents of a variable: | ||
3625 | <literallayout class='monospaced'> | ||
3626 | SRC_URI = "${SOURCEFORGE_MIRROR}/libpng/zlib-${PV}.tar.gz" | ||
3627 | </literallayout> | ||
3628 | <note> | ||
3629 | It is important to understand that the value of a | ||
3630 | variable expressed in this form does not get | ||
3631 | substituted automatically. | ||
3632 | The expansion of these expressions happens | ||
3633 | on-demand later (e.g. usually when a function that | ||
3634 | makes reference to the variable executes). | ||
3635 | This behavior ensures that the values are most | ||
3636 | appropriate for the context in which they are | ||
3637 | finally used. | ||
3638 | On the rare occasion that you do need the variable | ||
3639 | expression to be expanded immediately, you can use | ||
3640 | the <filename>:=</filename> operator instead of | ||
3641 | <filename>=</filename> when you make the | ||
3642 | assignment, but this is not generally needed. | ||
3643 | </note> | ||
3644 | </para></listitem> | ||
3645 | <listitem><para> | ||
3646 | <emphasis>Quote All Assignments ("<replaceable>value</replaceable>"):</emphasis> | ||
3647 | Use double quotes around values in all variable | ||
3648 | assignments (e.g. | ||
3649 | <filename>"<replaceable>value</replaceable>"</filename>). | ||
3650 | Following is an example: | ||
3651 | <literallayout class='monospaced'> | ||
3652 | VAR1 = "${OTHERVAR}" | ||
3653 | VAR2 = "The version is ${PV}" | ||
3654 | </literallayout> | ||
3655 | </para></listitem> | ||
3656 | <listitem><para> | ||
3657 | <emphasis>Conditional Assignment (?=):</emphasis> | ||
3658 | Conditional assignment is used to assign a | ||
3659 | value to a variable, but only when the variable is | ||
3660 | currently unset. | ||
3661 | Use the question mark followed by the equal sign | ||
3662 | (<filename>?=</filename>) to make a "soft" assignment | ||
3663 | used for conditional assignment. | ||
3664 | Typically, "soft" assignments are used in the | ||
3665 | <filename>local.conf</filename> file for variables | ||
3666 | that are allowed to come through from the external | ||
3667 | environment. | ||
3668 | </para> | ||
3669 | |||
3670 | <para>Here is an example where | ||
3671 | <filename>VAR1</filename> is set to "New value" if | ||
3672 | it is currently empty. | ||
3673 | However, if <filename>VAR1</filename> has already been | ||
3674 | set, it remains unchanged: | ||
3675 | <literallayout class='monospaced'> | ||
3676 | VAR1 ?= "New value" | ||
3677 | </literallayout> | ||
3678 | In this next example, <filename>VAR1</filename> | ||
3679 | is left with the value "Original value": | ||
3680 | <literallayout class='monospaced'> | ||
3681 | VAR1 = "Original value" | ||
3682 | VAR1 ?= "New value" | ||
3683 | </literallayout> | ||
3684 | </para></listitem> | ||
3685 | <listitem><para> | ||
3686 | <emphasis>Appending (+=):</emphasis> | ||
3687 | Use the plus character followed by the equals sign | ||
3688 | (<filename>+=</filename>) to append values to existing | ||
3689 | variables. | ||
3690 | <note> | ||
3691 | This operator adds a space between the existing | ||
3692 | content of the variable and the new content. | ||
3693 | </note></para> | ||
3694 | |||
3695 | <para>Here is an example: | ||
3696 | <literallayout class='monospaced'> | ||
3697 | SRC_URI += "file://fix-makefile.patch" | ||
3698 | </literallayout> | ||
3699 | </para></listitem> | ||
3700 | <listitem><para> | ||
3701 | <emphasis>Prepending (=+):</emphasis> | ||
3702 | Use the equals sign followed by the plus character | ||
3703 | (<filename>=+</filename>) to prepend values to existing | ||
3704 | variables. | ||
3705 | <note> | ||
3706 | This operator adds a space between the new content | ||
3707 | and the existing content of the variable. | ||
3708 | </note></para> | ||
3709 | |||
3710 | <para>Here is an example: | ||
3711 | <literallayout class='monospaced'> | ||
3712 | VAR =+ "Starts" | ||
3713 | </literallayout> | ||
3714 | </para></listitem> | ||
3715 | <listitem><para> | ||
3716 | <emphasis>Appending (_append):</emphasis> | ||
3717 | Use the <filename>_append</filename> operator to | ||
3718 | append values to existing variables. | ||
3719 | This operator does not add any additional space. | ||
3720 | Also, the operator is applied after all the | ||
3721 | <filename>+=</filename>, and | ||
3722 | <filename>=+</filename> operators have been applied and | ||
3723 | after all <filename>=</filename> assignments have | ||
3724 | occurred. | ||
3725 | </para> | ||
3726 | |||
3727 | <para>The following example shows the space being | ||
3728 | explicitly added to the start to ensure the appended | ||
3729 | value is not merged with the existing value: | ||
3730 | <literallayout class='monospaced'> | ||
3731 | SRC_URI_append = " file://fix-makefile.patch" | ||
3732 | </literallayout> | ||
3733 | You can also use the <filename>_append</filename> | ||
3734 | operator with overrides, which results in the actions | ||
3735 | only being performed for the specified target or | ||
3736 | machine: | ||
3737 | <literallayout class='monospaced'> | ||
3738 | SRC_URI_append_sh4 = " file://fix-makefile.patch" | ||
3739 | </literallayout> | ||
3740 | </para></listitem> | ||
3741 | <listitem><para> | ||
3742 | <emphasis>Prepending (_prepend):</emphasis> | ||
3743 | Use the <filename>_prepend</filename> operator to | ||
3744 | prepend values to existing variables. | ||
3745 | This operator does not add any additional space. | ||
3746 | Also, the operator is applied after all the | ||
3747 | <filename>+=</filename>, and | ||
3748 | <filename>=+</filename> operators have been applied and | ||
3749 | after all <filename>=</filename> assignments have | ||
3750 | occurred. | ||
3751 | </para> | ||
3752 | |||
3753 | <para>The following example shows the space being | ||
3754 | explicitly added to the end to ensure the prepended | ||
3755 | value is not merged with the existing value: | ||
3756 | <literallayout class='monospaced'> | ||
3757 | CFLAGS_prepend = "-I${S}/myincludes " | ||
3758 | </literallayout> | ||
3759 | You can also use the <filename>_prepend</filename> | ||
3760 | operator with overrides, which results in the actions | ||
3761 | only being performed for the specified target or | ||
3762 | machine: | ||
3763 | <literallayout class='monospaced'> | ||
3764 | CFLAGS_prepend_sh4 = "-I${S}/myincludes " | ||
3765 | </literallayout> | ||
3766 | </para></listitem> | ||
3767 | <listitem><para> | ||
3768 | <emphasis>Overrides:</emphasis> | ||
3769 | You can use overrides to set a value conditionally, | ||
3770 | typically based on how the recipe is being built. | ||
3771 | For example, to set the | ||
3772 | <ulink url='&YOCTO_DOCS_REF_URL;#var-KBRANCH'><filename>KBRANCH</filename></ulink> | ||
3773 | variable's value to "standard/base" for any target | ||
3774 | <ulink url='&YOCTO_DOCS_REF_URL;#var-MACHINE'><filename>MACHINE</filename></ulink>, | ||
3775 | except for qemuarm where it should be set to | ||
3776 | "standard/arm-versatile-926ejs", you would do the | ||
3777 | following: | ||
3778 | <literallayout class='monospaced'> | ||
3779 | KBRANCH = "standard/base" | ||
3780 | KBRANCH_qemuarm = "standard/arm-versatile-926ejs" | ||
3781 | </literallayout> | ||
3782 | Overrides are also used to separate alternate values | ||
3783 | of a variable in other situations. | ||
3784 | For example, when setting variables such as | ||
3785 | <ulink url='&YOCTO_DOCS_REF_URL;#var-FILES'><filename>FILES</filename></ulink> | ||
3786 | and | ||
3787 | <ulink url='&YOCTO_DOCS_REF_URL;#var-RDEPENDS'><filename>RDEPENDS</filename></ulink> | ||
3788 | that are specific to individual packages produced by | ||
3789 | a recipe, you should always use an override that | ||
3790 | specifies the name of the package. | ||
3791 | </para></listitem> | ||
3792 | <listitem><para> | ||
3793 | <emphasis>Indentation:</emphasis> | ||
3794 | Use spaces for indentation rather than than tabs. | ||
3795 | For shell functions, both currently work. | ||
3796 | However, it is a policy decision of the Yocto Project | ||
3797 | to use tabs in shell functions. | ||
3798 | Realize that some layers have a policy to use spaces | ||
3799 | for all indentation. | ||
3800 | </para></listitem> | ||
3801 | <listitem><para> | ||
3802 | <emphasis>Using Python for Complex Operations:</emphasis> | ||
3803 | For more advanced processing, it is possible to use | ||
3804 | Python code during variable assignments (e.g. | ||
3805 | search and replacement on a variable).</para> | ||
3806 | |||
3807 | <para>You indicate Python code using the | ||
3808 | <filename>${@<replaceable>python_code</replaceable>}</filename> | ||
3809 | syntax for the variable assignment: | ||
3810 | <literallayout class='monospaced'> | ||
3811 | SRC_URI = "ftp://ftp.info-zip.org/pub/infozip/src/zip${@d.getVar('PV',1).replace('.', '')}.tgz | ||
3812 | </literallayout> | ||
3813 | </para></listitem> | ||
3814 | <listitem><para> | ||
3815 | <emphasis>Shell Function Syntax:</emphasis> | ||
3816 | Write shell functions as if you were writing a shell | ||
3817 | script when you describe a list of actions to take. | ||
3818 | You should ensure that your script works with a generic | ||
3819 | <filename>sh</filename> and that it does not require | ||
3820 | any <filename>bash</filename> or other shell-specific | ||
3821 | functionality. | ||
3822 | The same considerations apply to various system | ||
3823 | utilities (e.g. <filename>sed</filename>, | ||
3824 | <filename>grep</filename>, <filename>awk</filename>, | ||
3825 | and so forth) that you might wish to use. | ||
3826 | If in doubt, you should check with multiple | ||
3827 | implementations - including those from BusyBox. | ||
3828 | </para></listitem> | ||
3829 | </itemizedlist> | ||
3830 | </para> | ||
3831 | </section> | ||
3508 | </section> | 3832 | </section> |
3509 | 3833 | ||
3510 | <section id="platdev-newmachine"> | 3834 | <section id="platdev-newmachine"> |
diff --git a/documentation/getting-started/getting-started-development-environment.xml b/documentation/getting-started/getting-started-development-environment.xml index 03a807e4a5..096517b729 100644 --- a/documentation/getting-started/getting-started-development-environment.xml +++ b/documentation/getting-started/getting-started-development-environment.xml | |||
@@ -17,7 +17,7 @@ | |||
17 | 17 | ||
18 | <para> | 18 | <para> |
19 | Specifically, this chapter addresses open source philosophy, workflows, | 19 | Specifically, this chapter addresses open source philosophy, workflows, |
20 | Git, source repositories, licensing, recipe syntax, and development | 20 | Git, source repositories, licensing, and development |
21 | syntax. | 21 | syntax. |
22 | </para> | 22 | </para> |
23 | 23 | ||
@@ -938,303 +938,6 @@ | |||
938 | </para> | 938 | </para> |
939 | </section> | 939 | </section> |
940 | 940 | ||
941 | <section id='recipe-syntax'> | ||
942 | <title>Recipe Syntax</title> | ||
943 | |||
944 | <para> | ||
945 | Understanding recipe file syntax is important for | ||
946 | writing recipes. | ||
947 | The following list overviews the basic items that make up a | ||
948 | BitBake recipe file. | ||
949 | For more complete BitBake syntax descriptions, see the | ||
950 | "<ulink url='&YOCTO_DOCS_BB_URL;#bitbake-user-manual-metadata'>Syntax and Operators</ulink>" | ||
951 | chapter of the BitBake User Manual. | ||
952 | <itemizedlist> | ||
953 | <listitem><para><emphasis>Variable Assignments and Manipulations:</emphasis> | ||
954 | Variable assignments allow a value to be assigned to a | ||
955 | variable. | ||
956 | The assignment can be static text or might include | ||
957 | the contents of other variables. | ||
958 | In addition to the assignment, appending and prepending | ||
959 | operations are also supported.</para> | ||
960 | <para>The following example shows some of the ways | ||
961 | you can use variables in recipes: | ||
962 | <literallayout class='monospaced'> | ||
963 | S = "${WORKDIR}/postfix-${PV}" | ||
964 | CFLAGS += "-DNO_ASM" | ||
965 | SRC_URI_append = " file://fixup.patch" | ||
966 | </literallayout> | ||
967 | </para></listitem> | ||
968 | <listitem><para><emphasis>Functions:</emphasis> | ||
969 | Functions provide a series of actions to be performed. | ||
970 | You usually use functions to override the default | ||
971 | implementation of a task function or to complement | ||
972 | a default function (i.e. append or prepend to an | ||
973 | existing function). | ||
974 | Standard functions use <filename>sh</filename> shell | ||
975 | syntax, although access to OpenEmbedded variables and | ||
976 | internal methods are also available.</para> | ||
977 | <para>The following is an example function from the | ||
978 | <filename>sed</filename> recipe: | ||
979 | <literallayout class='monospaced'> | ||
980 | do_install () { | ||
981 | autotools_do_install | ||
982 | install -d ${D}${base_bindir} | ||
983 | mv ${D}${bindir}/sed ${D}${base_bindir}/sed | ||
984 | rmdir ${D}${bindir}/ | ||
985 | } | ||
986 | </literallayout> | ||
987 | It is also possible to implement new functions that | ||
988 | are called between existing tasks as long as the | ||
989 | new functions are not replacing or complementing the | ||
990 | default functions. | ||
991 | You can implement functions in Python | ||
992 | instead of shell. | ||
993 | Both of these options are not seen in the majority of | ||
994 | recipes.</para></listitem> | ||
995 | <listitem><para><emphasis>Keywords:</emphasis> | ||
996 | BitBake recipes use only a few keywords. | ||
997 | You use keywords to include common | ||
998 | functions (<filename>inherit</filename>), load parts | ||
999 | of a recipe from other files | ||
1000 | (<filename>include</filename> and | ||
1001 | <filename>require</filename>) and export variables | ||
1002 | to the environment (<filename>export</filename>).</para> | ||
1003 | <para>The following example shows the use of some of | ||
1004 | these keywords: | ||
1005 | <literallayout class='monospaced'> | ||
1006 | export POSTCONF = "${STAGING_BINDIR}/postconf" | ||
1007 | inherit autoconf | ||
1008 | require otherfile.inc | ||
1009 | </literallayout> | ||
1010 | </para></listitem> | ||
1011 | <listitem><para><emphasis>Comments:</emphasis> | ||
1012 | Any lines that begin with the hash character | ||
1013 | (<filename>#</filename>) are treated as comment lines | ||
1014 | and are ignored: | ||
1015 | <literallayout class='monospaced'> | ||
1016 | # This is a comment | ||
1017 | </literallayout> | ||
1018 | </para></listitem> | ||
1019 | </itemizedlist> | ||
1020 | </para> | ||
1021 | |||
1022 | <para> | ||
1023 | This next list summarizes the most important and most commonly | ||
1024 | used parts of the recipe syntax. | ||
1025 | For more information on these parts of the syntax, you can | ||
1026 | reference the | ||
1027 | <ulink url='&YOCTO_DOCS_BB_URL;#bitbake-user-manual-metadata'>Syntax and Operators</ulink> | ||
1028 | chapter in the BitBake User Manual. | ||
1029 | <itemizedlist> | ||
1030 | <listitem><para><emphasis>Line Continuation: <filename>\</filename></emphasis> - | ||
1031 | Use the backward slash (<filename>\</filename>) | ||
1032 | character to split a statement over multiple lines. | ||
1033 | Place the slash character at the end of the line that | ||
1034 | is to be continued on the next line: | ||
1035 | <literallayout class='monospaced'> | ||
1036 | VAR = "A really long \ | ||
1037 | line" | ||
1038 | </literallayout> | ||
1039 | <note> | ||
1040 | You cannot have any characters including spaces | ||
1041 | or tabs after the slash character. | ||
1042 | </note> | ||
1043 | </para></listitem> | ||
1044 | <listitem><para> | ||
1045 | <emphasis>Using Variables: <filename>${...}</filename></emphasis> - | ||
1046 | Use the <filename>${<replaceable>VARNAME</replaceable>}</filename> syntax to | ||
1047 | access the contents of a variable: | ||
1048 | <literallayout class='monospaced'> | ||
1049 | SRC_URI = "${SOURCEFORGE_MIRROR}/libpng/zlib-${PV}.tar.gz" | ||
1050 | </literallayout> | ||
1051 | <note> | ||
1052 | It is important to understand that the value of a | ||
1053 | variable expressed in this form does not get | ||
1054 | substituted automatically. | ||
1055 | The expansion of these expressions happens | ||
1056 | on-demand later (e.g. usually when a function that | ||
1057 | makes reference to the variable executes). | ||
1058 | This behavior ensures that the values are most | ||
1059 | appropriate for the context in which they are | ||
1060 | finally used. | ||
1061 | On the rare occasion that you do need the variable | ||
1062 | expression to be expanded immediately, you can use | ||
1063 | the <filename>:=</filename> operator instead of | ||
1064 | <filename>=</filename> when you make the | ||
1065 | assignment, but this is not generally needed. | ||
1066 | </note> | ||
1067 | </para></listitem> | ||
1068 | <listitem><para><emphasis>Quote All Assignments: <filename>"<replaceable>value</replaceable>"</filename></emphasis> - | ||
1069 | Use double quotes around the value in all variable | ||
1070 | assignments. | ||
1071 | <literallayout class='monospaced'> | ||
1072 | VAR1 = "${OTHERVAR}" | ||
1073 | VAR2 = "The version is ${PV}" | ||
1074 | </literallayout> | ||
1075 | </para></listitem> | ||
1076 | <listitem><para><emphasis>Conditional Assignment: <filename>?=</filename></emphasis> - | ||
1077 | Conditional assignment is used to assign a value to | ||
1078 | a variable, but only when the variable is currently | ||
1079 | unset. | ||
1080 | Use the question mark followed by the equal sign | ||
1081 | (<filename>?=</filename>) to make a "soft" assignment | ||
1082 | used for conditional assignment. | ||
1083 | Typically, "soft" assignments are used in the | ||
1084 | <filename>local.conf</filename> file for variables | ||
1085 | that are allowed to come through from the external | ||
1086 | environment. | ||
1087 | </para> | ||
1088 | <para>Here is an example where | ||
1089 | <filename>VAR1</filename> is set to "New value" if | ||
1090 | it is currently empty. | ||
1091 | However, if <filename>VAR1</filename> has already been | ||
1092 | set, it remains unchanged: | ||
1093 | <literallayout class='monospaced'> | ||
1094 | VAR1 ?= "New value" | ||
1095 | </literallayout> | ||
1096 | In this next example, <filename>VAR1</filename> | ||
1097 | is left with the value "Original value": | ||
1098 | <literallayout class='monospaced'> | ||
1099 | VAR1 = "Original value" | ||
1100 | VAR1 ?= "New value" | ||
1101 | </literallayout> | ||
1102 | </para></listitem> | ||
1103 | <listitem><para><emphasis>Appending: <filename>+=</filename></emphasis> - | ||
1104 | Use the plus character followed by the equals sign | ||
1105 | (<filename>+=</filename>) to append values to existing | ||
1106 | variables. | ||
1107 | <note> | ||
1108 | This operator adds a space between the existing | ||
1109 | content of the variable and the new content. | ||
1110 | </note></para> | ||
1111 | <para>Here is an example: | ||
1112 | <literallayout class='monospaced'> | ||
1113 | SRC_URI += "file://fix-makefile.patch" | ||
1114 | </literallayout> | ||
1115 | </para></listitem> | ||
1116 | <listitem><para><emphasis>Prepending: <filename>=+</filename></emphasis> - | ||
1117 | Use the equals sign followed by the plus character | ||
1118 | (<filename>=+</filename>) to prepend values to existing | ||
1119 | variables. | ||
1120 | <note> | ||
1121 | This operator adds a space between the new content | ||
1122 | and the existing content of the variable. | ||
1123 | </note></para> | ||
1124 | <para>Here is an example: | ||
1125 | <literallayout class='monospaced'> | ||
1126 | VAR =+ "Starts" | ||
1127 | </literallayout> | ||
1128 | </para></listitem> | ||
1129 | <listitem><para><emphasis>Appending: <filename>_append</filename></emphasis> - | ||
1130 | Use the <filename>_append</filename> operator to | ||
1131 | append values to existing variables. | ||
1132 | This operator does not add any additional space. | ||
1133 | Also, the operator is applied after all the | ||
1134 | <filename>+=</filename>, and | ||
1135 | <filename>=+</filename> operators have been applied and | ||
1136 | after all <filename>=</filename> assignments have | ||
1137 | occurred. | ||
1138 | </para> | ||
1139 | <para>The following example shows the space being | ||
1140 | explicitly added to the start to ensure the appended | ||
1141 | value is not merged with the existing value: | ||
1142 | <literallayout class='monospaced'> | ||
1143 | SRC_URI_append = " file://fix-makefile.patch" | ||
1144 | </literallayout> | ||
1145 | You can also use the <filename>_append</filename> | ||
1146 | operator with overrides, which results in the actions | ||
1147 | only being performed for the specified target or | ||
1148 | machine: | ||
1149 | <literallayout class='monospaced'> | ||
1150 | SRC_URI_append_sh4 = " file://fix-makefile.patch" | ||
1151 | </literallayout> | ||
1152 | </para></listitem> | ||
1153 | <listitem><para><emphasis>Prepending: <filename>_prepend</filename></emphasis> - | ||
1154 | Use the <filename>_prepend</filename> operator to | ||
1155 | prepend values to existing variables. | ||
1156 | This operator does not add any additional space. | ||
1157 | Also, the operator is applied after all the | ||
1158 | <filename>+=</filename>, and | ||
1159 | <filename>=+</filename> operators have been applied and | ||
1160 | after all <filename>=</filename> assignments have | ||
1161 | occurred. | ||
1162 | </para> | ||
1163 | <para>The following example shows the space being | ||
1164 | explicitly added to the end to ensure the prepended | ||
1165 | value is not merged with the existing value: | ||
1166 | <literallayout class='monospaced'> | ||
1167 | CFLAGS_prepend = "-I${S}/myincludes " | ||
1168 | </literallayout> | ||
1169 | You can also use the <filename>_prepend</filename> | ||
1170 | operator with overrides, which results in the actions | ||
1171 | only being performed for the specified target or | ||
1172 | machine: | ||
1173 | <literallayout class='monospaced'> | ||
1174 | CFLAGS_prepend_sh4 = "-I${S}/myincludes " | ||
1175 | </literallayout> | ||
1176 | </para></listitem> | ||
1177 | <listitem><para><emphasis>Overrides:</emphasis> - | ||
1178 | You can use overrides to set a value conditionally, | ||
1179 | typically based on how the recipe is being built. | ||
1180 | For example, to set the | ||
1181 | <ulink url='&YOCTO_DOCS_REF_URL;#var-KBRANCH'><filename>KBRANCH</filename></ulink> | ||
1182 | variable's value to "standard/base" for any target | ||
1183 | <ulink url='&YOCTO_DOCS_REF_URL;#var-MACHINE'><filename>MACHINE</filename></ulink>, | ||
1184 | except for qemuarm where it should be set to | ||
1185 | "standard/arm-versatile-926ejs", you would do the | ||
1186 | following: | ||
1187 | <literallayout class='monospaced'> | ||
1188 | KBRANCH = "standard/base" | ||
1189 | KBRANCH_qemuarm = "standard/arm-versatile-926ejs" | ||
1190 | </literallayout> | ||
1191 | Overrides are also used to separate alternate values | ||
1192 | of a variable in other situations. | ||
1193 | For example, when setting variables such as | ||
1194 | <ulink url='&YOCTO_DOCS_REF_URL;#var-FILES'><filename>FILES</filename></ulink> | ||
1195 | and | ||
1196 | <ulink url='&YOCTO_DOCS_REF_URL;#var-RDEPENDS'><filename>RDEPENDS</filename></ulink> | ||
1197 | that are specific to individual packages produced by | ||
1198 | a recipe, you should always use an override that | ||
1199 | specifies the name of the package. | ||
1200 | </para></listitem> | ||
1201 | <listitem><para><emphasis>Indentation:</emphasis> | ||
1202 | Use spaces for indentation rather than than tabs. | ||
1203 | For shell functions, both currently work. | ||
1204 | However, it is a policy decision of the Yocto Project | ||
1205 | to use tabs in shell functions. | ||
1206 | Realize that some layers have a policy to use spaces | ||
1207 | for all indentation. | ||
1208 | </para></listitem> | ||
1209 | <listitem><para><emphasis>Using Python for Complex Operations: <filename>${@<replaceable>python_code</replaceable>}</filename></emphasis> - | ||
1210 | For more advanced processing, it is possible to use | ||
1211 | Python code during variable assignments (e.g. | ||
1212 | search and replacement on a variable).</para> | ||
1213 | <para>You indicate Python code using the | ||
1214 | <filename>${@<replaceable>python_code</replaceable>}</filename> | ||
1215 | syntax for the variable assignment: | ||
1216 | <literallayout class='monospaced'> | ||
1217 | SRC_URI = "ftp://ftp.info-zip.org/pub/infozip/src/zip${@d.getVar('PV',1).replace('.', '')}.tgz | ||
1218 | </literallayout> | ||
1219 | </para></listitem> | ||
1220 | <listitem><para><emphasis>Shell Function Syntax:</emphasis> | ||
1221 | Write shell functions as if you were writing a shell | ||
1222 | script when you describe a list of actions to take. | ||
1223 | You should ensure that your script works with a generic | ||
1224 | <filename>sh</filename> and that it does not require | ||
1225 | any <filename>bash</filename> or other shell-specific | ||
1226 | functionality. | ||
1227 | The same considerations apply to various system | ||
1228 | utilities (e.g. <filename>sed</filename>, | ||
1229 | <filename>grep</filename>, <filename>awk</filename>, | ||
1230 | and so forth) that you might wish to use. | ||
1231 | If in doubt, you should check with multiple | ||
1232 | implementations - including those from BusyBox. | ||
1233 | </para></listitem> | ||
1234 | </itemizedlist> | ||
1235 | </para> | ||
1236 | </section> | ||
1237 | |||
1238 | <section id="development-concepts"> | 941 | <section id="development-concepts"> |
1239 | <title>Development Concepts</title> | 942 | <title>Development Concepts</title> |
1240 | 943 | ||