ch33_11.htm

the unix power tools

CLASS="literal"
>close</CODE
></DT
><DD
CLASS="listitem"
><P
CLASS="para"
><BLOCKQUOTE
CLASS="screen"
><PRE
CLASS="screen"
><CODE
CLASS="literal"
>close(</CODE
><CODE
CLASS="replaceable"
><I
>filename-expr</I
></CODE
><CODE
CLASS="literal"
>)</CODE
>
<CODE
CLASS="literal"
>close(</CODE
><CODE
CLASS="replaceable"
><I
>command-expr</I
></CODE
><CODE
CLASS="literal"
>)</CODE
></PRE
></BLOCKQUOTE
>
In some implementations of <EM
CLASS="emphasis"
>awk</EM
>, you can have only ten files open<A
CLASS="indexterm"
NAME="AUTOID-37624"
></A
>
simultaneously and one pipe; modern versions allow more than one pipe open.
Therefore, <EM
CLASS="emphasis"
>nawk</EM
> provides a <EM
CLASS="emphasis"
>close</EM
>
statement that allows you to close a file or a pipe. <EM
CLASS="emphasis"
>close</EM
> takes
as an argument the same expression that opened the pipe
or file. (<EM
CLASS="emphasis"
>nawk</EM
>)</P
></DD
><DT
CLASS="term"
><CODE
CLASS="literal"
>continue</CODE
></DT
><DD
CLASS="listitem"
><P
CLASS="para"
>Begin next iteration of <EM
CLASS="emphasis"
>while</EM
>, <EM
CLASS="emphasis"
>for</EM
>, or <EM
CLASS="emphasis"
>do</EM
> loop immediately.<A
CLASS="indexterm"
NAME="AUTOID-37638"
></A
>&#13;</P
></DD
><DT
CLASS="term"
><CODE
CLASS="literal"
>cos</CODE
></DT
><DD
CLASS="listitem"
><P
CLASS="para"
><CODE
CLASS="literal"
>cos(</CODE
><CODE
CLASS="replaceable"
><I
>x</I
></CODE
><CODE
CLASS="literal"
>)</CODE
>

Return cosine of <CODE
CLASS="replaceable"
><I
>x</I
></CODE
> (in radians).<A
CLASS="indexterm"
NAME="AUTOID-37649"
></A
>
(<EM
CLASS="emphasis"
>nawk</EM
>)&#13;</P
></DD
><DT
CLASS="term"
><CODE
CLASS="literal"
>delete</CODE
></DT
><DD
CLASS="listitem"
><P
CLASS="para"
><CODE
CLASS="literal"
>delete </CODE
><CODE
CLASS="replaceable"
><I
>array</I
></CODE
>[<CODE
CLASS="replaceable"
><I
>element</I
></CODE
>]<CODE
CLASS="literal"
> </CODE
>

Delete <CODE
CLASS="replaceable"
><I
>element</I
></CODE
> of <CODE
CLASS="replaceable"
><I
>array</I
></CODE
>. (<EM
CLASS="emphasis"
>nawk</EM
>)<A
CLASS="indexterm"
NAME="AUTOID-37664"
></A
>&#13;</P
></DD
><DT
CLASS="term"
><CODE
CLASS="literal"
>do</CODE
></DT
><DD
CLASS="listitem"
><P
CLASS="para"
><BLOCKQUOTE
CLASS="screen"
><PRE
CLASS="screen"
><CODE
CLASS="literal"
>do</CODE
>
     <CODE
CLASS="replaceable"
><I
>body</I
></CODE
><CODE
CLASS="literal"
>while (</CODE
><CODE
CLASS="replaceable"
><I
>expr</I
></CODE
><CODE
CLASS="literal"
>)</CODE
></PRE
></BLOCKQUOTE
>
Looping statement.<A
CLASS="indexterm"
NAME="AUTOID-37677"
></A
>
Execute statements in <CODE
CLASS="replaceable"
><I
>body</I
></CODE
>, then evaluate <CODE
CLASS="replaceable"
><I
>expr</I
></CODE
>.
If <CODE
CLASS="replaceable"
><I
>expr</I
></CODE
> is true, execute <CODE
CLASS="replaceable"
><I
>body</I
></CODE
> again.
More than one <CODE
CLASS="replaceable"
><I
>command</I
></CODE
> must be put inside braces (<CODE
CLASS="literal"
>{}</CODE
>).
(<EM
CLASS="emphasis"
>nawk</EM
>)&#13;</P
></DD
><DT
CLASS="term"
><CODE
CLASS="literal"
>exit</CODE
></DT
><DD
CLASS="listitem"
><P
CLASS="para"
><CODE
CLASS="literal"
>exit</CODE
>[<CODE
CLASS="replaceable"
><I
>expr</I
></CODE
>]

Do not execute remaining instructions and do not read new input.<A
CLASS="indexterm"
NAME="AUTOID-37693"
></A
>
END
procedure, if any, will be executed.
The <CODE
CLASS="literal"
>expr</CODE
>, if any, becomes <EM
CLASS="emphasis"
>awk</EM
>'s 
<SPAN
CLASS="link"
>exit status (<A
CLASS="linkend"
HREF="ch44_07.htm"
TITLE="Exit Status of UNIX Processes "
>44.7</A
>)</SPAN
>.&#13;</P
></DD
><DT
CLASS="term"
><CODE
CLASS="literal"
>exp</CODE
></DT
><DD
CLASS="listitem"
><P
CLASS="para"
><CODE
CLASS="literal"
>exp(</CODE
><CODE
CLASS="replaceable"
><I
>arg</I
></CODE
><CODE
CLASS="literal"
>)&#13;</CODE
>Return the natural exponent of <CODE
CLASS="replaceable"
><I
>arg</I
></CODE
>.<A
CLASS="indexterm"
NAME="AUTOID-37707"
></A
>&#13;</P
></DD
><DT
CLASS="term"
><CODE
CLASS="literal"
>for</CODE
></DT
><DD
CLASS="listitem"
><P
CLASS="para"
><CODE
CLASS="literal"
>for (</CODE
>[<CODE
CLASS="replaceable"
><I
>init-expr</I
></CODE
>]<CODE
CLASS="literal"
>; </CODE
>[<CODE
CLASS="replaceable"
><I
>test-expr</I
></CODE
>]<CODE
CLASS="literal"
>; </CODE
>[<CODE
CLASS="replaceable"
><I
>incr-expr</I
></CODE
>]<CODE
CLASS="literal"
>)</CODE
>
    <CODE
CLASS="replaceable"
><I
>command</I
></CODE
>
C-language-style looping construct.<A
CLASS="indexterm"
NAME="AUTOID-37722"
></A
>
Typically, <CODE
CLASS="replaceable"
><I
>init-expr</I
></CODE
> assigns the initial value of a counter
variable.
<CODE
CLASS="replaceable"
><I
>test-expr</I
></CODE
> is a relational expression that is evaluated each time
before executing the <CODE
CLASS="replaceable"
><I
>command</I
></CODE
>.
When <CODE
CLASS="replaceable"
><I
>test-expr</I
></CODE
> is false, the loop is exited.
<CODE
CLASS="replaceable"
><I
>incr-expr</I
></CODE
> is used to increment the counter variable after each pass.
A series of <CODE
CLASS="replaceable"
><I
>command</I
></CODE
>s
must be put within braces (<CODE
CLASS="literal"
>{}</CODE
>).

Example:</P
><P
CLASS="para"
><BLOCKQUOTE
CLASS="screen"
><PRE
CLASS="screen"
>for (i = 1; i &lt;= 10; i++)
     printf &quot;Element %d is %s.\n&quot;, i, array[i]</PRE
></BLOCKQUOTE
></P
><P
CLASS="para"
></P
></DD
><DT
CLASS="term"
><CODE
CLASS="literal"
>for</CODE
></DT
><DD
CLASS="listitem"
><P
CLASS="para"
><CODE
CLASS="literal"
>for (</CODE
><CODE
CLASS="replaceable"
><I
>item </I
></CODE
><CODE
CLASS="literal"
>in </CODE
><CODE
CLASS="replaceable"
><I
>array</I
></CODE
><CODE
CLASS="literal"
>)</CODE
>
     <CODE
CLASS="replaceable"
><I
>command</I
></CODE
>
For each <CODE
CLASS="replaceable"
><I
>item</I
></CODE
> in an associative <CODE
CLASS="replaceable"
><I
>array</I
></CODE
>, do
<CODE
CLASS="replaceable"
><I
>command</I
></CODE
>.
More than one <CODE
CLASS="replaceable"
><I
>command</I
></CODE
> must be put inside braces (<CODE
CLASS="literal"
>{}</CODE
>).
Refer to each element of the array as <CODE
CLASS="replaceable"
><I
>array</I
></CODE
><CODE
CLASS="literal"
>[</CODE
><CODE
CLASS="replaceable"
><I
>item</I
></CODE
><CODE
CLASS="literal"
>]</CODE
>.
&#13;</P
></DD
><DT
CLASS="term"
><CODE
CLASS="literal"
>getline</CODE
></DT
><DD
CLASS="listitem"
><P
CLASS="para"
><CODE
CLASS="literal"
>getline </CODE
>[<CODE
CLASS="replaceable"
><I
>var</I
></CODE
>][<CODE
CLASS="literal"
>&lt;</CODE
><CODE
CLASS="replaceable"
><I
>file</I
></CODE
>]
        or
<CODE
CLASS="replaceable"
><I
>command </I
></CODE
><CODE
CLASS="literal"
>| getline </CODE
>[<CODE
CLASS="replaceable"
><I
>var</I
></CODE
>]
Read next line of input.
Original <EM
CLASS="emphasis"
>awk</EM
> does not support the syntax
to open multiple input streams.
The first form reads input from <CODE
CLASS="replaceable"
><I
>file</I
></CODE
>,
and the second form reads the standard output of a UNIX <CODE
CLASS="replaceable"
><I
>command</I
></CODE
>.
Both forms read one line at a time, and each time
the statement is executed it gets the next line
of input.
The line of input is assigned to <CODE
CLASS="literal"
>$0</CODE
>,
and it is parsed into fields, setting <EM
CLASS="emphasis"
>NF</EM
>,
<EM
CLASS="emphasis"
>NR</EM
>, and <EM
CLASS="emphasis"
>FNR</EM
>.
If <CODE
CLASS="replaceable"
><I
>var</I
></CODE
> is specified, the result is assigned
to <CODE
CLASS="replaceable"
><I
>var</I
></CODE
> and the <CODE
CLASS="literal"
>$0</CODE
> is not changed.
Thus, if
the result is assigned to a variable, the
current line does not change.
<EM
CLASS="emphasis"
>getline</EM
> is actually a function and it returns 1 if it
reads a record successfully, 0 if end-of-file is
encountered, and -1 if for some reason it is
otherwise unsuccessful. (<EM
CLASS="emphasis"
>nawk</EM
>)&#13;</P
></DD
><DT
CLASS="term"
><CODE
CLASS="literal"
>gsub</CODE
></DT
><DD
CLASS="listitem"
><P
CLASS="para"
><CODE
CLASS="literal"
>gsub(</CODE
><CODE
CLASS="replaceable"
><I
>r</I
></CODE
><CODE
CLASS="literal"
>,</CODE
><CODE
CLASS="replaceable"
><I
>s</I
></CODE
>[<CODE
CLASS="literal"
>,</CODE
><CODE
CLASS="replaceable"
><I
>t</I
></CODE
>]<CODE
CLASS="literal"
>)</CODE
>

Globally substitute <CODE
CLASS="replaceable"
><I
>s</I
></CODE
> for each match of the<A
CLASS="indexterm"
NAME="AUTOID-37791"
></A
>
regular expression <CODE
CLASS="replaceable"
><I
>r</I
></CODE
> in the string <CODE
CLASS="replaceable"
><I
>t</I
></CODE
>.
Return
the number of substitutions.
If <CODE
CLASS="replaceable"
><I
>t</I
></CODE
> is not supplied,
defaults to <CODE
CLASS="literal"
>$0</CODE
>. (<EM
CLASS="emphasis"
>nawk</EM
>)&#13;</P
></DD
><DT
CLASS="term"
><CODE
CLASS="literal"
>if</CODE
></DT
><DD
CLASS="listitem"
><P
CLASS="para"
><CODE
CLASS="literal"
>if (</CODE
><CODE
CLASS="replaceable"
><I
>condition</I
></CODE
><CODE
CLASS="literal"
>)</CODE
></P
><P
CLASS="para"
><BLOCKQUOTE
CLASS="screen"
><PRE
CLASS="screen"
>      <CODE
CLASS="replaceable"
><I
>command</I
></CODE
>
[<CODE
CLASS="literal"
>else</CODE
>
      <CODE
CLASS="replaceable"
><I
>command</I
></CODE
>]</PRE
></BLOCKQUOTE
></P
><P
CLASS="para"
>If <CODE
CLASS="replaceable"
><I
>condition</I
></CODE
> is true, do <CODE
CLASS="replaceable"
><I
>command(s)</I
></CODE
>, otherwise do<A
CLASS="indexterm"
NAME="AUTOID-37814"
></A
>
<CODE
CLASS="replaceable"
><I
>command(s)</I
></CODE
> in <EM
CLASS="emphasis"
>else</EM
> clause (if any).
<CODE
CLASS="replaceable"
><I
>condition</I
></CODE
> can be an expression that uses 
any of the relational operators <CODE
CLASS="literal"
>&lt;</CODE
>, <CODE
CLASS="literal"
>&lt;=</CODE
>, <CODE
CLASS="literal"
>==</CODE
>, 
<CODE
CLASS="literal"
>!=</CODE
>, <CODE
CLASS="literal"
>&gt;=</CODE
>, or <CODE
CLASS="literal"
>&gt;</CODE
>, as well as
the pattern-matching operators <CODE
CLASS="literal"
>~</CODE
> or <CODE
CLASS="literal"
>!~</CODE
>
(e.g., <CODE
CLASS="literal"
>if&nbsp;($1&nbsp;~&nbsp;/[Aa].*[Zz]/)</CODE
>).
A series of <CODE
CLASS="replaceable"
><I
>command</I
></CODE
>s must be put within braces (<CODE
CLASS="literal"
>{}</CODE
>).</P
></DD
><DT
CLASS="term"
><CODE
CLASS="literal"
>index</CODE
></DT
><DD
CLASS="listitem"
><P
CLASS="para"
><CODE
CLASS="literal"
>index(</CODE
><CODE
CLASS="replaceable"
><I
>str</I
></CODE
><CODE
CLASS="literal"
>,</CODE
><CODE
CLASS="replaceable"
><I
>substr</I
></CODE
><CODE
CLASS="literal"
>)</CODE
>

Return position of first substring <CODE
CLASS="replaceable"
><I
>substr</I
></CODE
> in string <CODE
CLASS="replaceable"
><I
>str</I
></CODE
><A
CLASS="indexterm"
NAME="AUTOID-37842"
></A
>
or 0 if not found.&#13;</P
></DD
><DT
CLASS="term"
><CODE
CLASS="literal"
>int</CODE
></DT
><DD
CLASS="listitem"
><P
CLASS="para"
><CODE
CLASS="literal"
>int(</CODE
><CODE
CLASS="replaceable"
><I
>arg</I
></CODE
><CODE
CLASS="literal"
>)</CODE
>

Return integer value of <CODE
CLASS="replaceable"
><I
>arg</I
></CODE
>.<A
CLASS="indexterm"
NAME="AUTOID-37853"
></A
>&#13;</P
></DD
><DT
CLASS="term"
><CODE
CLASS="literal"
>length</CODE
></DT
><DD
CLASS="listitem"
><P
CLASS="para"
><CODE
CLASS="literal"
>length(</CODE
><CODE
CLASS="replaceable"
><I
>arg</I
></CODE
><CODE
CLASS="literal"
>)</CODE
>

Return the length of <CODE
CLASS="replaceable"
><I
>arg</I
></CODE
>.<A
CLASS="indexterm"
NAME="AUTOID-37864"
></A
>&#13;</P
></DD
><DT
CLASS="term"
><CODE
CLASS="literal"
>log</CODE
></DT
><DD
CLASS="listitem"
><P
CLASS="para"
><CODE
CLASS="literal"
>log(</CODE
><CODE
CLASS="replaceable"
><I
>arg</I
></CODE
><CODE
CLASS="literal"
>)</CODE
>

Return the natural logarithm of <CODE
CLASS="replaceable"
><I
>arg</I
></CODE
>.<A
CLASS="indexterm"
NAME="AUTOID-37875"
></A
>&#13;</P
></DD
><DT
CLASS="term"
><CODE
CLASS="literal"
>match</CODE
></DT
><DD
CLASS="listitem"
><P
CLASS="para"
><CODE
CLASS="literal"
>match(</CODE
><CODE
CLASS="replaceable"
><I
>s</I
></CODE
><CODE
CLASS="literal"
>,</CODE
><CODE
CLASS="replaceable"
><I
>r</I
></CODE
><CODE
CLASS="literal"
>)</CODE
>

Function that matches the pattern, specified by the regular expression<A
CLASS="indexterm"
NAME="AUTOID-37887"
></A
>
<CODE
CLASS="replaceable"
><I
>r</I
></CODE
>, in the string <CODE
CLASS="replaceable"
><I
>s</I
></CODE
> and returns either the position in
<CODE
CLASS="replaceable"
><I
>s</I
></CODE
> where the match begins or 0 if no occurrences are found.
Sets the values of <EM
CLASS="emphasis"
>RSTART</EM
> and <EM
CLASS="emphasis"
>RLENGTH</EM
>. (<EM
CLASS="emphasis"
>nawk</EM
>)
&#13;</P
></DD
><DT
CLASS="term"
><CODE
CLASS="literal"
>next</CODE
></DT
><DD
CLASS="listitem"
><P
CLASS="para"
>Read next input line and start new cycle through pattern/procedures
statements.<A
CLASS="indexterm"
NAME="AUTOID-37900"
></A
>&#13;</P
></DD
><DT
CLASS="term"
><CODE
CLASS="literal"
>print</CODE
></DT
><DD
CLASS="listitem"
><P
CLASS="para"
><CODE
CLASS="literal"
>print </CODE
>[<CODE
CLASS="replaceable"
><I
>args</I
></CODE
>] [<CODE
CLASS="replaceable"
><I
>destination</I
></CODE
>]

Print <CODE
CLASS="replaceable"
><I
>args</I
></CODE
> on output, followed by a newline.<A
CLASS="indexterm"
NAME="AUTOID-37911"
></A
>
<CODE
CLASS="replaceable"
><I
>args</I
></CODE
> is usually one or more fields,
but may also be one or more of the predefined variables&nbsp;- or
arbitrary expressions.
If no <CODE
CLASS="replaceable"
><I
>args</I
></CODE
> are given, prints <CODE
CLASS="literal"
>$0</CODE