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single quotes. Example (from NixOS):
job = ''
start on network-interfaces
start script
rm -f /var/run/opengl-driver
${if videoDriver == "nvidia"
then "ln -sf ${nvidiaDrivers} /var/run/opengl-driver"
else if cfg.driSupport
then "ln -sf ${mesa} /var/run/opengl-driver"
else ""
}
rm -f /var/log/slim.log
end script
'';
This style has two big advantages:
- \, ' and " aren't special, only '' and ${. So you get a lot less
escaping in shell scripts / configuration files in Nixpkgs/NixOS.
The delimiter '' is rare in scripts (and can usually be written as
""). ${ is also fairly rare.
Other delimiters such as <<...>>, {{...}} and <|...|> were also
considered but this one appears to have the fewest drawbacks
(thanks Martin).
- Indentation is intelligently stripped so that multi-line strings
can follow the nesting structure of the containing Nix
expression. E.g. in the example above 6 spaces are stripped from
the start of each line. This prevents unnecessary indentation in
generated files (which sometimes even breaks things).
See tests/lang/eval-okay-ind-string.nix for some examples.
107 lines
3 KiB
Nix
107 lines
3 KiB
Nix
let
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s1 = ''
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This is an indented multi-line string
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literal. An amount of whitespace at
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the start of each line matching the minimum
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indentation of all lines in the string
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literal together will be removed. Thus,
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in this case four spaces will be
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stripped from each line, even though
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THIS LINE is indented six spaces.
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Also, empty lines don't count in the
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determination of the indentation level (the
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previous empty line has indentation 0, but
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it doesn't matter).
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'';
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s2 = '' If the string starts with whitespace
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followed by a newline, it's stripped, but
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that's not the case here. Two spaces are
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stripped because of the " " at the start.
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'';
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s3 = ''
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This line is indented
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a bit further.
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''; # indentation of last line doesn't count if it's empty
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s4 = ''
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Anti-quotations, like ${if true then "so" else "not so"}, are
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also allowed.
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'';
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s5 = ''
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The \ is not special here.
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' can be followed by any character except another ', e.g. 'x'.
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Likewise for $, e.g. $$ or $varName.
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But ' followed by ' is special, as is $ followed by {.
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If you want them, use anti-quotations: ${"''"}, ${"\${"}.
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'';
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s6 = ''
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Tabs are not interpreted as whitespace (since we can't guess
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what tab settings are intended), so don't use them.
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This line starts with a space and a tab, so only one
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space will be stripped from each line.
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'';
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s7 = ''
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Also note that if the last line (just before the closing ' ')
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consists only of whitespace, it's ignored. But here there is
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some non-whitespace stuff, so the line isn't removed. '';
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s8 = '' ${""}
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This shows a hacky way to preserve an empty line after the start.
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But there's no reason to do so: you could just repeat the empty
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line.
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'';
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s9 = ''
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${""} Similarly you can force an indentation level,
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in this case to 2 spaces. This works because the anti-quote
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is significant (not whitespace).
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'';
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s10 = ''
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'';
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s11 = '''';
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s12 = '' '';
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s13 = ''
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start on network-interfaces
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start script
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rm -f /var/run/opengl-driver
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${if true
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then "ln -sf 123 /var/run/opengl-driver"
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else if true
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then "ln -sf 456 /var/run/opengl-driver"
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else ""
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}
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rm -f /var/log/slim.log
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end script
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env SLIM_CFGFILE=${"abc"}
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env SLIM_THEMESDIR=${"def"}
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env FONTCONFIG_FILE=/etc/fonts/fonts.conf # !!! cleanup
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env XKB_BINDIR=${"foo"}/bin # Needed for the Xkb extension.
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env LD_LIBRARY_PATH=${"libX11"}/lib:${"libXext"}/lib:/usr/lib/ # related to xorg-sys-opengl - needed to load libglx for (AI)GLX support (for compiz)
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${if true
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then "env XORG_DRI_DRIVER_PATH=${"nvidiaDrivers"}/X11R6/lib/modules/drivers/"
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else if true
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then "env XORG_DRI_DRIVER_PATH=${"mesa"}/lib/modules/dri"
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else ""
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}
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exec ${"slim"}/bin/slim
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'';
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in s1 + s2 + s3 + s4 + s5 + s6 + s7 + s8 + s9 + s10 + s11 + s12 + s13
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