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Shell: Update section on input validation

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Also mention safety of [[ $var =~ regexp ]].
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Florian Weimer 2014-10-10 16:44:53 +02:00
parent 01cf74aac0
commit e23c383775
1 changed files with 21 additions and 15 deletions
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defensive-coding/en-US/Shell.xml
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@ -162,6 +162,14 @@ external-program "$arg1" "$arg2"
evaluation, even with integer operators such as
<literal>-eq</literal>.)
</para>
<para>
The conditional expression
“<literal>[[ $</literal><emphasis>variable</emphasis><literal> =~ </literal><emphasis>regexp</emphasis><literal> ]]</literal>”
can be used for input validation, assuming that
<emphasis>regexp</emphasis> is a constant regular
expression.
See <xref linkend="sect-Defensive_Coding-Shell-Input_Validation"/>.
</para>
</listitem>
<listitem>
<para>
@ -391,29 +399,27 @@ trap cleanup 0
</para>
<para>
The following construct can be used to check if a string
“<literal>$value</literal>” is not a non-negative integer.
“<literal>$value</literal>” is an integer.
</para>
<informalexample>
<programlisting language="Bash">
case "$value" in
*[!0-9]*)
echo "invalid input value" 1>&amp;2
exit 1
;;
esac
if [[ $value =~ ^-?[0-9]$ ]] ; then
echo value is an integer
else
echo "value is not an integer" 1>&amp;2
exit 1
fi
</programlisting>
</informalexample>
<para>
The pattern “<literal>*[!0-9]*</literal>” is not special shell
syntax—it matches any string which contains arbitrary characters,
followed by a non-digit, followed by arbitrary characters.
Using <literal>case</literal> statements for input validation is
also possible, but the pattern language is more restrictive, and
it can be difficult to write suitable patterns.
</para>
<para>
Using <literal>case</literal> statements is the most reliable way
for performing input validation, although constructing proper
patterns is difficult. The <literal>expr</literal> external
command and the built-in operator <literal>=~</literal> can give
misleading results.
The <literal>expr</literal> external command can give misleading
results (e.g., if the value being checked contains operators
itself) and should not be used.
</para>
</section>
<section id="sect-Defensive_Coding-Shell-Edit_Guard">