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6d6c68c0d2
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.
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Str("This is an indented multi-line string\nliteral. An amount of whitespace at\nthe start of each line matching the minimum\nindentation of all lines in the string\nliteral together will be removed. Thus,\nin this case four spaces will be\nstripped from each line, even though\n THIS LINE is indented six spaces.\n\nAlso, empty lines don't count in the\ndetermination of the indentation level (the\nprevious empty line has indentation 0, but\nit doesn't matter).\nIf the string starts with whitespace\n followed by a newline, it's stripped, but\n that's not the case here. Two spaces are\n stripped because of the \" \" at the start. \nThis line is indented\na bit further.\nAnti-quotations, like so, are\nalso allowed.\n The \\ is not special here.\n' can be followed by any character except another ', e.g. 'x'.\nLikewise for $, e.g. $$ or $varName.\nBut ' followed by ' is special, as is $ followed by {.\nIf you want them, use anti-quotations: '', ${.\n Tabs are not interpreted as whitespace (since we can't guess\n what tab settings are intended), so don't use them.\n\tThis line starts with a space and a tab, so only one\n space will be stripped from each line.\nAlso note that if the last line (just before the closing ' ')\nconsists only of whitespace, it's ignored. But here there is\nsome non-whitespace stuff, so the line isn't removed. \nThis shows a hacky way to preserve an empty line after the start.\nBut there's no reason to do so: you could just repeat the empty\nline.\n Similarly you can force an indentation level,\n in this case to 2 spaces. This works because the anti-quote\n is significant (not whitespace).\nstart on network-interfaces\n\nstart script\n\n rm -f /var/run/opengl-driver\n ln -sf 123 /var/run/opengl-driver\n\n rm -f /var/log/slim.log\n \nend script\n\nenv SLIM_CFGFILE=abc\nenv SLIM_THEMESDIR=def\nenv FONTCONFIG_FILE=/etc/fonts/fonts.conf \t\t\t\t# !!! cleanup\nenv XKB_BINDIR=foo/bin \t\t\t\t# Needed for the Xkb extension.\nenv LD_LIBRARY_PATH=libX11/lib:libXext/lib:/usr/lib/ # related to xorg-sys-opengl - needed to load libglx for (AI)GLX support (for compiz)\n\nenv XORG_DRI_DRIVER_PATH=nvidiaDrivers/X11R6/lib/modules/drivers/ \n\nexec slim/bin/slim\n",[])
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