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man: clarify Environmentfile format

Remove incorrect claim that C escapes (such as \t and \n) are recognized and that control characters are disallowed. Specify the allowed characters and escapes with single quotes, with double quotes, and without quotes.
This commit is contained in:
Yonathan Randolph 2021-12-26 17:12:00 -08:00 committed by Yu Watanabe
parent de4fe289cf
commit 4bbcde8498

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@ -2513,18 +2513,39 @@ SystemCallErrorNumber=EPERM</programlisting>
<varlistentry>
<term><varname>EnvironmentFile=</varname></term>
<listitem><para>Similar to <varname>Environment=</varname> but reads the environment variables from a text
file. The text file should contain new-line-separated variable assignments. Empty lines, lines without an
<literal>=</literal> separator, or lines starting with ; or # will be ignored, which may be used for
commenting. A line ending with a backslash will be concatenated with the following one, allowing multiline
variable definitions. The parser strips leading and trailing whitespace from the values of assignments, unless
you use double quotes (").</para>
<listitem><para>Similar to <varname>Environment=</varname> but reads the environment variables from a text file.
The text file should contain newline-separated variable assignments. Empty lines, lines without an
<literal>=</literal> separator, or lines starting with <literal>;</literal> or <literal>#</literal> will be
ignored, which may be used for commenting. The file must be UTF-8 encoded. Valid characters are <ulink
url="https://www.unicode.org/glossary/#unicode_scalar_value">unicode scalar values</ulink> other than <ulink
url="https://www.unicode.org/glossary/#noncharacter">noncharacters</ulink>, U+0000 NUL, and U+FEFF <ulink
url="https://www.unicode.org/glossary/#byte_order_mark">byte order mark</ulink>. Control codes other than NUL
are allowed.</para>
<para><ulink url="https://en.wikipedia.org/wiki/Escape_sequences_in_C#Table_of_escape_sequences">C escapes</ulink>
are supported, but not
<ulink url="https://en.wikipedia.org/wiki/Control_character#In_ASCII">most control characters</ulink>.
<literal>\t</literal> and <literal>\n</literal> can be used to insert tabs and newlines within
<varname>EnvironmentFile=</varname>.</para>
<para>In the file, an unquoted value after the <literal>=</literal> is parsed with the same backslash-escape
rules as <ulink
url="https://pubs.opengroup.org/onlinepubs/9699919799/utilities/V3_chap02.html#tag_18_02_01">unquoted
text</ulink> in a POSIX shell, but unlike in a shell, interior whitespace is preserved and quotes after the
first non-whitespace character are preserved. Leading and trailing whitespace (space, tab, carriage return) is
discarded, but interior whitespace within the line is preserved verbatim. A line ending with a backslash will be
continued to the following one, with the newline itself discarded. A backslash
<literal>\</literal> followed by any character other than newline will preserve the following character, so that
<literal>\\</literal> will become the value <literal>\</literal>.</para>
<para>In the file, a <literal>'</literal>-quoted value after the <literal>=</literal> can span multiple lines
and contain any character verbatim other than single quote, like <ulink
url="https://pubs.opengroup.org/onlinepubs/9699919799/utilities/V3_chap02.html#tag_18_02_02">single-quoted
text</ulink> in a POSIX shell. No backslash-escape sequences are recognized. Leading and trailing whitespace
outside of the single quotes is discarded.</para>
<para>In the file, a <literal>"</literal>-quoted value after the <literal>=</literal> can span multiple lines,
and the same escape sequences are recognized as in <ulink
url="https://pubs.opengroup.org/onlinepubs/9699919799/utilities/V3_chap02.html#tag_18_02_03">double-quoted
text</ulink> of a POSIX shell. Backslash (<literal>\</literal>) followed by any of <literal>"\`$</literal> will
preserve that character. A backslash followed by newline is a line continuation, and the newline itself is
discarded. A backslash followed by any other character is ignored; both the backslash and the following
character are preserved verbatim. Leading and trailing whitespace outside of the double quotes is
discarded.</para>
<para>The argument passed should be an absolute filename or wildcard expression, optionally prefixed with
<literal>-</literal>, which indicates that if the file does not exist, it will not be read and no error or
@ -2557,12 +2578,6 @@ SystemCallErrorNumber=EPERM</programlisting>
<para>Variables set for invoked processes due to this setting are subject to being overridden by those
configured with <varname>Environment=</varname> or <varname>EnvironmentFile=</varname>.</para>
<para><ulink url="https://en.wikipedia.org/wiki/Escape_sequences_in_C#Table_of_escape_sequences">C escapes</ulink>
are supported, but not
<ulink url="https://en.wikipedia.org/wiki/Control_character#In_ASCII">most control characters</ulink>.
<literal>\t</literal> and <literal>\n</literal> can be used to insert tabs and newlines within
<varname>EnvironmentFile=</varname>.</para>
<para>Example:
<programlisting>PassEnvironment=VAR1 VAR2 VAR3</programlisting>
passes three variables <literal>VAR1</literal>,