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<TITLE>Linux Unleashed, Third Edition:Shell Programming</TITLE>
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<!--TITLE=Linux Unleashed, Third Edition//-->
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<H3><A NAME="Heading8"></A><FONT COLOR="#000077">The test Command</FONT></H3>
<P>In <TT>bash</TT> and <TT>pdksh</TT>, a command called <TT>test</TT> is used to evaluate conditional expressions. You would typically use the <TT>test</TT> command to evaluate a condition that is used in a conditional statement or to evaluate the entrance or exit criteria for an iteration statement. The <TT>test</TT> command has the following syntax:</P>
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test <I>expression</I>
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<P>or
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[ <I>expression</I> ]
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<P>Several built-in operators can be used with the <TT>test</TT> command. These operators can be classified into four groups: integer operators, string operators, file operators, and logical operators.</P>
<P>The shell integer operators perform similar functions to the string operators except that they act on integer arguments. Table 14.2 lists the <TT>test</TT> command’s integer operators.</P>
<TABLE WIDTH="100%"><CAPTION ALIGN=LEFT><B>Table 14.2.</B> The <TT>test</TT> command’s integer operators.
<TR>
<TH COLSPAN="2"><HR>
<TR>
<TH ALIGN="LEFT" WIDTH="30%">Operator
<TH ALIGN="LEFT" WIDTH="70%">Meaning
<TR>
<TH COLSPAN="2"><HR>
<TR>
<TD><TT>int1 -eq int2</TT>
<TD>Returns True if int1 is equal to int2.
<TR>
<TD><TT>int1 -ge int2</TT>
<TD>Returns True if int1 is greater than or equal to int2.
<TR>
<TD><TT>int1 -gt int2</TT>
<TD>Returns True if int1 is greater than int2.
<TR>
<TD><TT>int1 -le int2</TT>
<TD>Returns True if int1 is less than or equal to int2.
<TR>
<TD><TT>int1 -lt int2</TT>
<TD>Returns True if int1 is less than int2.
<TR>
<TD><TT>int1 -ne int2</TT>
<TD>Returns True if int1 is not equal to int2.
<TR>
<TD COLSPAN="2"><HR>
</TABLE>
<P>The string operators are used to evaluate string expressions. Table 14.3 lists the string operators that are supported by the three shell programming languages.
</P>
<TABLE WIDTH="100%"><CAPTION ALIGN=LEFT><B>Table 14.3.</B> The <TT>test</TT> command’s string operators.
<TR>
<TH COLSPAN="2"><HR>
<TR>
<TH ALIGN="LEFT" WIDTH="30%">Operator
<TH ALIGN="LEFT" WIDTH="70%">Meaning
<TR>
<TH COLSPAN="2"><HR>
<TR>
<TD><TT>str1 = str2</TT>
<TD>Returns True if str1 is identical to str2.
<TR>
<TD><TT>str1 != str2</TT>
<TD>Returns True if str1 is not identical to str2.
<TR>
<TD><TT>str</TT>
<TD>Returns True if str is not null.
<TR>
<TD><TT>-n str</TT>
<TD>Returns True if the length of str is greater than zero.
<TR>
<TD><TT>-z str</TT>
<TD>Returns True if the length of str is equal to zero.
<TR>
<TD COLSPAN="2"><HR>
</TABLE>
<P>The <TT>test</TT> command’s file operators are used to perform functions such as checking to see whether a file exists and checking to see what kind of file is passed as an argument to the <TT>test</TT> command. Table 14.4 lists the <TT>test</TT> command’s file operators.</P>
<TABLE WIDTH="100%"><CAPTION ALIGN=LEFT><B>Table 14.4.</B> The <TT>test</TT> command’s file operators.
<TR>
<TH COLSPAN="2"><HR>
<TR>
<TH ALIGN="LEFT" WIDTH="30%">Operator
<TH ALIGN="LEFT" WIDTH="70%">Meaning
<TR>
<TH COLSPAN="2"><HR>
<TR>
<TD><TT>-d filename</TT>
<TD>Returns True if file, filename is a directory.
<TR>
<TD><TT>-f filename</TT>
<TD>Returns True if file, filename is an ordinary file.
<TR>
<TD><TT>-r filename</TT>
<TD>Returns True if file, filename can be read by the process.
<TR>
<TD><TT>-s filename</TT>
<TD>Returns True if file, filename has a nonzero length.
<TR>
<TD><TT>-w filename</TT>
<TD>Returns True if file, filename can be written by the process.
<TR>
<TD><TT>-x filename</TT>
<TD>Returns True if file, filename is executable.
<TR>
<TD COLSPAN="2"><HR>
</TABLE>
<P>The <TT>test</TT> command’s logical operators are used to combine two or more of the integer, string, or file operators or to negate a single integer, string, or file operator. Table 14.5 lists the <TT>test</TT> command’s logical operators.</P>
<TABLE WIDTH="100%"><CAPTION ALIGN=LEFT><B>Table 14.5.</B> The <TT>test</TT> command’s logical operators.
<TR>
<TH COLSPAN="2"><HR>
<TR>
<TH ALIGN="LEFT" WIDTH="30%">Command
<TH ALIGN="LEFT" WIDTH="70%">Meaning
<TR>
<TH COLSPAN="2"><HR>
<TR>
<TD><TT>! expr</TT>
<TD>Returns True if expr is not true.
<TR>
<TD><TT>expr1 -a expr2</TT>
<TD>Returns True if expr1 and expr2 are true.
<TR>
<TD><TT>expr1 -o expr2</TT>
<TD>Returns True if expr1 or expr2 is true.
<TR>
<TD COLSPAN="2"><HR>
</TABLE>
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