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basic: support default and alternate values for env expansion 

Sometimes it's useful to provide a default value during an environment
expansion, if the environment variable isn't already set.

For instance $XDG_DATA_DIRS is suppose to default to:

/usr/local/share/:/usr/share/

if it's not yet set. That means callers wishing to augment
XDG_DATA_DIRS need to manually add those two values.

This commit changes replace_env to support the following shell
compatible default value syntax:

XDG_DATA_DIRS=/foo:${XDG_DATA_DIRS:-/usr/local/share/:/usr/share}

Likewise, it's useful to provide an alternate value during an
environment expansion, if the environment variable isn't already set.

For instance, $LD_LIBRARY_PATH will inadvertently search the current
working directory if it starts or ends with a colon, so the following
is usually wrong:

LD_LIBRARY_PATH=/foo/lib:${LD_LIBRARY_PATH}

To address that, this changes replace_env to support the following
shell compatible alternate value syntax:

LD_LIBRARY_PATH=/foo/lib${LD_LIBRARY_PATH:+:${LD_LIBRARY_PATH}}

[zj: gate the new syntax under REPLACE_ENV_ALLOW_EXTENDED switch, so
existing callers are not modified.]
This commit is contained in:
Ray Strode 2016-08-09 10:20:22 -04:00 committed by Zbigniew Jędrzejewski-Szmek
parent 4bed076c5f
commit b82f58bfe3
6 changed files with 108 additions and 12 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

16
man/environment.d.xml
View File

@ -78,8 +78,16 @@
<literal><replaceable>KEY</replaceable>=<replaceable>VALUE</replaceable></literal> environment
variable assignments, separated by newlines. The right hand side of these assignments may
reference previously defined environment variables, using the <literal>${OTHER_KEY}</literal>
and <literal>$OTHER_KEY</literal> format. No other elements of shell syntax are supported.
</para>
and <literal>$OTHER_KEY</literal> format. It is also possible to use
<literal>${<replaceable>FOO</replaceable>:-<replaceable>DEFAULT_VALUE</replaceable>}</literal>
to expand in the same way as <literal>${<replaceable>FOO</replaceable>}</literal> unless the
expansion would be empty, in which case it expands to <replaceable>DEFAULT_VALUE</replaceable>,
and use
<literal>${<replaceable>FOO</replaceable>:+<replaceable>ALTERNATE_VALUE</replaceable>}</literal>
to expand to <replaceable>ALTERNATE_VALUE</replaceable> as long as
<literal>${<replaceable>FOO</replaceable>}</literal> would have expanded to a non-empty value.
No other elements of shell syntax are supported.</para>
<para>Each<replaceable>KEY</replaceable> must be a valid variable name. Empty lines
and lines beginning with the comment character <literal>#</literal> are ignored.</para>
@ -95,8 +103,8 @@
<programlisting>
FOO_DEBUG=force-software-gl,log-verbose
PATH=/opt/foo/bin:$PATH
LD_LIBRARY_PATH=/opt/foo/lib
XDG_DATA_DIRS=/opt/foo/share:${XDG_DATA_DIRS}
LD_LIBRARY_PATH=${LD_LIBRARY_PATH:+:$LD_LIBRARY_PATH}/opt/foo/lib
XDG_DATA_DIRS=/opt/foo/share:${XDG_DATA_DIRS:-/usr/local/share/:/usr/share/}
</programlisting>
</example>
</refsect2>

67
src/basic/env-util.c
View File

@ -525,12 +525,16 @@ char *replace_env_n(const char *format, size_t n, char **env, unsigned flags) {
CURLY,
VARIABLE,
VARIABLE_RAW,
TEST,
DEFAULT_VALUE,
ALTERNATE_VALUE,
} state = WORD;
const char *e, *word = format;
const char *e, *word = format, *test_value;
char *k;
_cleanup_free_ char *r = NULL;
size_t i;
size_t i, len;
int nest = 0;
assert(format);
@ -554,7 +558,7 @@ char *replace_env_n(const char *format, size_t n, char **env, unsigned flags) {
word = e-1;
state = VARIABLE;
nest++;
} else if (*e == '$') {
k = strnappend(r, word, e-word);
if (!k)
@ -594,6 +598,63 @@ char *replace_env_n(const char *format, size_t n, char **env, unsigned flags) {
free(r);
r = k;
word = e+1;
state = WORD;
} else if (*e == ':') {
if (!(flags & REPLACE_ENV_ALLOW_EXTENDED))
/* Treat this as unsupported syntax, i.e. do no replacement */
state = WORD;
else {
len = e-word-2;
state = TEST;
}
}
break;
case TEST:
if (*e == '-')
state = DEFAULT_VALUE;
else if (*e == '+')
state = ALTERNATE_VALUE;
else {
state = WORD;
break;
}
test_value = e+1;
break;
case DEFAULT_VALUE: /* fall through */
case ALTERNATE_VALUE:
assert(flags & REPLACE_ENV_ALLOW_EXTENDED);
if (*e == '{') {
nest++;
break;
}
if (*e != '}')
break;
nest--;
if (nest == 0) { // || !strchr(e+1, '}')) {
const char *t;
_cleanup_free_ char *v = NULL;
t = strv_env_get_n(env, word+2, len, flags);
if (t && state == ALTERNATE_VALUE)
t = v = replace_env_n(test_value, e-test_value, env, flags);
else if (!t && state == DEFAULT_VALUE)
t = v = replace_env_n(test_value, e-test_value, env, flags);
k = strappend(r, t);
if (!k)
return NULL;
free(r);
r = k;
word = e+1;
state = WORD;
}

1
src/basic/env-util.h
View File

@ -32,6 +32,7 @@ bool env_assignment_is_valid(const char *e);
enum {
REPLACE_ENV_USE_ENVIRONMENT = 1u,
REPLACE_ENV_ALLOW_BRACELESS = 2u,
REPLACE_ENV_ALLOW_EXTENDED = 4u,
};
char *replace_env_n(const char *format, size_t n, char **env, unsigned flags);

6
src/basic/fileio.c
View File

@ -784,7 +784,9 @@ static int merge_env_file_push(
}
expanded_value = replace_env(value, *env,
REPLACE_ENV_USE_ENVIRONMENT|REPLACE_ENV_ALLOW_BRACELESS);
REPLACE_ENV_USE_ENVIRONMENT|
REPLACE_ENV_ALLOW_BRACELESS|
REPLACE_ENV_ALLOW_EXTENDED);
if (!expanded_value)
return -ENOMEM;
@ -799,7 +801,7 @@ int merge_env_file(
const char *fname) {
/* NOTE: this function supports braceful and braceless variable expansions,
* unlike other exported parsing functions.
* plus "extended" substitutions, unlike other exported parsing functions.
*/
return parse_env_file_internal(f, fname, NEWLINE, merge_env_file_push, env, NULL);

14
src/test/test-env-util.c
View File

@ -185,6 +185,12 @@ static void test_replace_env_argv(void) {
"${FOO",
"FOO$$${FOO}",
"$$FOO${FOO}",
"${FOO:-${BAR}}",
"${QUUX:-${FOO}}",
"${FOO:+${BAR}}",
"${QUUX:+${BAR}}",
"${FOO:+|${BAR}|}}",
"${FOO:+|${BAR}{|}",
NULL
};
_cleanup_strv_free_ char **r = NULL;
@ -202,7 +208,13 @@ static void test_replace_env_argv(void) {
assert_se(streq(r[8], "${FOO"));
assert_se(streq(r[9], "FOO$BAR BAR"));
assert_se(streq(r[10], "$FOOBAR BAR"));
assert_se(strv_length(r) == 11);
assert_se(streq(r[11], "${FOO:-waldo}"));
assert_se(streq(r[12], "${QUUX:-BAR BAR}"));
assert_se(streq(r[13], "${FOO:+waldo}"));
assert_se(streq(r[14], "${QUUX:+waldo}"));
assert_se(streq(r[15], "${FOO:+|waldo|}}"));
assert_se(streq(r[16], "${FOO:+|waldo{|}"));
assert_se(strv_length(r) == 17);
}
static void test_env_clean(void) {

16
src/test/test-fileio.c
View File

@ -229,6 +229,10 @@ static void test_merge_env_file(void) {
"twentytwo=2${one}\n"
"xxx_minus_three=$xxx - 3\n"
"xxx=0x$one$one$one\n"
"yyy=${one:-fallback}\n"
"zzz=${one:+replacement}\n"
"zzzz=${foobar:-${nothing}}\n"
"zzzzz=${nothing:+${nothing}}\n"
, false);
assert(r >= 0);
@ -245,7 +249,11 @@ static void test_merge_env_file(void) {
assert_se(streq(a[3], "twentytwo=22"));
assert_se(streq(a[4], "xxx=0x222"));
assert_se(streq(a[5], "xxx_minus_three= - 3"));
assert_se(a[6] == NULL);
assert_se(streq(a[6], "yyy=2"));
assert_se(streq(a[7], "zzz=replacement"));
assert_se(streq(a[8], "zzzz="));
assert_se(streq(a[9], "zzzzz="));
assert_se(a[10] == NULL);
r = merge_env_file(&a, NULL, t);
assert_se(r >= 0);
@ -260,7 +268,11 @@ static void test_merge_env_file(void) {
assert_se(streq(a[3], "twentytwo=22"));
assert_se(streq(a[4], "xxx=0x222"));
assert_se(streq(a[5], "xxx_minus_three=0x222 - 3"));
assert_se(a[6] == NULL);
assert_se(streq(a[6], "yyy=2"));
assert_se(streq(a[7], "zzz=replacement"));
assert_se(streq(a[8], "zzzz="));
assert_se(streq(a[9], "zzzzz="));
assert_se(a[10] == NULL);
}
static void test_merge_env_file_invalid(void) {