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Fix example of how to escape data in psql backslash commands.

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This commit is contained in:
Tom Lane 2006-05-31 22:34:35 +00:00
parent c6d3c1b817
commit 2703007501
1 changed files with 13 additions and 16 deletions
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29
doc/src/sgml/ref/psql-ref.sgml
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@ -1,5 +1,5 @@
<!-- <!--
$PostgreSQL: pgsql/doc/src/sgml/ref/psql-ref.sgml,v 1.164 2006/05/31 11:47:20 momjian Exp $ $PostgreSQL: pgsql/doc/src/sgml/ref/psql-ref.sgml,v 1.165 2006/05/31 22:34:35 tgl Exp $
PostgreSQL documentation PostgreSQL documentation
--> -->
@ -2265,27 +2265,24 @@ testdb=&gt; <userinput>SELECT * FROM :foo;</userinput>
testdb=&gt; <userinput>\set content '''' `cat my_file.txt` ''''</userinput> testdb=&gt; <userinput>\set content '''' `cat my_file.txt` ''''</userinput>
testdb=&gt; <userinput>INSERT INTO my_table VALUES (:content);</userinput> testdb=&gt; <userinput>INSERT INTO my_table VALUES (:content);</userinput>
</programlisting> </programlisting>
One possible problem with this approach is that <filename>my_file.txt</filename> One problem with this approach is that <filename>my_file.txt</filename>
might contain single quotes. These need to be escaped so that 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 they don't cause a syntax error when the second line is processed. This
could be done with the program <command>sed</command>: could be done with the program <command>sed</command>:
<programlisting> <programlisting>
testdb=&gt; <userinput>\set content '''' `sed -e "s/'/\\\\''/g" &lt; my_file.txt` ''''</userinput> testdb=&gt; <userinput>\set content '''' `sed -e "s/'/''/g" &lt; my_file.txt` ''''</userinput>
</programlisting> </programlisting>
Observe the correct number of backslashes (6)! It works If you are using non-standard-conforming strings then you'll also need
this way: After <application>psql</application> has parsed this to double backslashes. This is a bit tricky:
line, it passes <literal>sed -e "s/'/\\''/g" &lt; my_file.txt</literal> <programlisting>
to the shell. The shell will do its own thing inside the double testdb=&gt; <userinput>\set content '''' `sed -e "s/'/''/g" -e 's/\\/\\\\/g' &lt; my_file.txt` ''''</userinput>
quotes and execute <command>sed</command> with the arguments </programlisting>
<literal>-e</literal> and <literal>s/'/''/g</literal>. When Note the use of different shell quoting conventions so that neither
<command>sed</command> parses this it will replace the two the single quote marks nor the backslashes are special to the shell.
backslashes with a single one and then do the substitution. Perhaps 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 at one point you thought it was great that all Unix commands use the
same escape character. And this is ignoring the fact that you might same escape character.)
have to escape all backslashes as well because
<acronym>SQL</acronym> text constants are also subject to certain
interpretations. In that case you might be better off preparing the
file externally.
</para> </para>
<para> <para>