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Allow psql variables to be interpolated with literal or identifier escaping.

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Loosely based on a patch by Pavel Stehule.
This commit is contained in:
Robert Haas 2010-01-29 17:44:12 +00:00
parent 76be0c81cc
commit d0cfc01823
2 changed files with 123 additions and 37 deletions
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80
doc/src/sgml/ref/psql-ref.sgml
View File

@ -1,5 +1,5 @@
<!--
$PostgreSQL: pgsql/doc/src/sgml/ref/psql-ref.sgml,v 1.236 2009/12/24 23:36:39 tgl Exp $
$PostgreSQL: pgsql/doc/src/sgml/ref/psql-ref.sgml,v 1.237 2010/01/29 17:44:12 rhaas Exp $
PostgreSQL documentation
-->
@ -658,7 +658,12 @@ testdb=&gt;
<para>
If an unquoted argument begins with a colon (<literal>:</literal>),
it is taken as a <application>psql</> variable and the value of the
variable is used as the argument instead.
variable is used as the argument instead. If the variable name is
surrounded by single quotes (e.g. <literal>:'var'</literal>), it
will be escaped as an SQL literal and the result will be used as
the argument. If the variable name is surrounded by double quotes,
it will be escaped as an SQL identifier and the result will be used
as the argument.
</para>
<para>
@ -2711,18 +2716,35 @@ bar
<para>
An additional useful feature of <application>psql</application>
variables is that you can substitute (<quote>interpolate</quote>)
them into regular <acronym>SQL</acronym> statements. The syntax for
this is again to prepend the variable name with a colon
them into regular <acronym>SQL</acronym> statements.
<application>psql</application> provides special facilities for
ensuring that values used as SQL literals and identifiers are
properly escaped. The syntax for interpolating a value without
any special escaping is again to prepend the variable name with a colon
(<literal>:</literal>):
<programlisting>
testdb=&gt; <userinput>\set foo 'my_table'</userinput>
testdb=&gt; <userinput>SELECT * FROM :foo;</userinput>
</programlisting>
would then query the table <literal>my_table</literal>. The value of
the variable is copied literally, so it can even contain unbalanced
quotes or backslash commands. You must make sure that it makes sense
where you put it. Variable interpolation will not be performed into
quoted <acronym>SQL</acronym> entities.
would then query the table <literal>my_table</literal>. Note that this
may be unsafe: the value of the variable is copied literally, so it can
even contain unbalanced quotes or backslash commands. You must make sure
that it makes sense where you put it.
</para>
<para>
When a value is to be used as an SQL literal or identifier, it is
safest to arrange for it to be escaped. To escape the value of
a variable as an SQL literal, write a colon followed by the variable
name in single quotes. To escape the value an SQL identifier, write
a colon followed by the variable name in double quotes. The previous
example would be more safely written this way:
<programlisting>
testdb=&gt; <userinput>\set foo 'my_table'</userinput>
testdb=&gt; <userinput>SELECT * FROM :"foo";</userinput>
</programlisting>
Variable interpolation will not be performed into quoted
<acronym>SQL</acronym> entities.
</para>
<para>
@ -2730,40 +2752,26 @@ testdb=&gt; <userinput>SELECT * FROM :foo;</userinput>
copy the contents of a file into a table column. First load the file into a
variable and then proceed as above:
<programlisting>
testdb=&gt; <userinput>\set content '''' `cat my_file.txt` ''''</userinput>
testdb=&gt; <userinput>INSERT INTO my_table VALUES (:content);</userinput>
testdb=&gt; <userinput>\set content `cat my_file.txt`</userinput>
testdb=&gt; <userinput>INSERT INTO my_table VALUES (:'content');</userinput>
</programlisting>
One problem with this approach is that <filename>my_file.txt</filename>
might contain single quotes. These need to be escaped so that
they don't cause a syntax error when the second line is processed. This
could be done with the program <command>sed</command>:
<programlisting>
testdb=&gt; <userinput>\set content '''' `sed -e "s/'/''/g" &lt; my_file.txt` ''''</userinput>
</programlisting>
If you are using non-standard-conforming strings then you'll also need
to double backslashes. This is a bit tricky:
<programlisting>
testdb=&gt; <userinput>\set content '''' `sed -e "s/'/''/g" -e 's/\\/\\\\/g' &lt; my_file.txt` ''''</userinput>
</programlisting>
Note the use of different shell quoting conventions so that neither
the single quote marks nor the backslashes are special to the shell.
Backslashes are still special to <command>sed</command>, however, so
we need to double them. (Perhaps
at one point you thought it was great that all Unix commands use the
same escape character.)
(Note that this still won't work if my_file.txt contains NUL bytes.
psql does not support embedded NUL bytes in variable values.)
</para>
<para>
Since colons can legally appear in SQL commands, the following rule
applies: the character sequence
<quote>:name</quote> is not changed unless <quote>name</> is the name
of a variable that is currently set. In any case you can escape
a colon with a backslash to protect it from substitution. (The
colon syntax for variables is standard <acronym>SQL</acronym> for
Since colons can legally appear in SQL commands, an apparent attempt
at interpolation (such as <literal>:name</literal>,
<literal>:'name'</literal>, or <literal>:"name"</literal>) is not
changed unless the named variable is currently set. In any case you
can escape a colon with a backslash to protect it from substitution.
(The colon syntax for variables is standard <acronym>SQL</acronym> for
embedded query languages, such as <application>ECPG</application>.
The colon syntax for array slices and type casts are
<productname>PostgreSQL</productname> extensions, hence the
conflict.)
conflict. The colon syntax for escaping a variable's value as an
SQL literal or identifier is a <application>psql</application>
extension.)
</para>
</refsect3>

80
src/bin/psql/psqlscan.l
View File

@ -33,7 +33,7 @@
* Portions Copyright (c) 1994, Regents of the University of California
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/bin/psql/psqlscan.l,v 1.31 2010/01/02 16:57:59 momjian Exp $
* $PostgreSQL: pgsql/src/bin/psql/psqlscan.l,v 1.32 2010/01/29 17:44:12 rhaas Exp $
*
*-------------------------------------------------------------------------
*/
@ -118,6 +118,7 @@ static YY_BUFFER_STATE prepare_buffer(const char *txt, int len,
char **txtcopy);
static void emit(const char *txt, int len);
static bool is_utf16_surrogate_first(uint32 c);
static void escape_variable(bool as_ident);
#define ECHO emit(yytext, yyleng)
@ -707,6 +708,14 @@ other .
}
}
:'[A-Za-z0-9_]+' {
escape_variable(false);
}
:\"[A-Za-z0-9_]+\" {
escape_variable(true);
}
/*
* Back to backend-compatible rules.
*/
@ -927,6 +936,27 @@ other .
return LEXRES_OK;
}
:'[A-Za-z0-9_]+' {
if (option_type == OT_VERBATIM)
ECHO;
else
{
escape_variable(false);
return LEXRES_OK;
}
}
:\"[A-Za-z0-9_]+\" {
if (option_type == OT_VERBATIM)
ECHO;
else
{
escape_variable(true);
return LEXRES_OK;
}
}
"|" {
ECHO;
if (option_type == OT_FILEPIPE)
@ -1740,3 +1770,51 @@ is_utf16_surrogate_first(uint32 c)
{
return (c >= 0xD800 && c <= 0xDBFF);
}
static void
escape_variable(bool as_ident)
{
char saved_char;
const char *value;
/* Variable lookup. */
saved_char = yytext[yyleng - 1];
yytext[yyleng - 1] = '\0';
value = GetVariable(pset.vars, yytext + 2);
/* Escaping. */
if (value)
{
if (!pset.db)
psql_error("can't escape without active connection\n");
else
{
char *escaped_value;
if (as_ident)
escaped_value =
PQescapeIdentifier(pset.db, value, strlen(value));
else
escaped_value =
PQescapeLiteral(pset.db, value, strlen(value));
if (escaped_value == NULL)
{
const char *error = PQerrorMessage(pset.db);
psql_error("%s", error);
}
else
{
appendPQExpBufferStr(output_buf, escaped_value);
PQfreemem(escaped_value);
return;
}
}
}
/*
* If we reach this point, some kind of error has occurred. Emit the
* original text into the output buffer.
*/
yytext[yyleng - 1] = saved_char;
emit(yytext, yyleng);
}