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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
-->
@ -2265,27 +2265,24 @@ testdb=&gt; <userinput>SELECT * FROM :foo;</userinput>
testdb=&gt; <userinput>\set content '''' `cat my_file.txt` ''''</userinput>
testdb=&gt; <userinput>INSERT INTO my_table VALUES (:content);</userinput>
</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
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>
testdb=&gt; <userinput>\set content '''' `sed -e "s/'/''/g" &lt; my_file.txt` ''''</userinput>
</programlisting>
Observe the correct number of backslashes (6)! It works
this way: After <application>psql</application> has parsed this
line, it passes <literal>sed -e "s/'/\\''/g" &lt; my_file.txt</literal>
to the shell. The shell will do its own thing inside the double
quotes and execute <command>sed</command> with the arguments
<literal>-e</literal> and <literal>s/'/''/g</literal>. When
<command>sed</command> parses this it will replace the two
backslashes with a single one and then do the substitution. Perhaps
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. And this is ignoring the fact that you might
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.
same escape character.)
</para>
<para>