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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2 Final//EN"><html><head><!-- Copyright 1997 The Open Group, All Rights Reserved --><title>notation</title></head><body bgcolor=white><center><font size=2>The Single UNIX &reg; Specification, Version 2<br>Copyright &copy; 1997 The Open Group</font></center><hr size=2 noshade><blockquote><center><h2><a name = "tag_006">&nbsp;</a>File Format Notation</h2></center><xref type="1" name="filefmt"></xref>The<b>STDIN</b>,<b>STDOUT</b>,<b>STDERR</b>,<b>INPUT FILES</b>and<b>OUTPUT FILES</b>sections of the utility descriptions usea syntax to describe thedata organisation within the files,when that organisation is not otherwise obvious.The syntax is similar to that used by the <b>XSH</b> specification<i><a href="../xsh/printf.html">printf()</a></i>function, as described in this chapter.When used in<b>STDIN</b>or<b>INPUT FILES</b>sections of the utility descriptions,this syntax describes the format that could have been used to write thetext to be read, not a format that could be used by the <i><a href="../xsh/scanf.html">scanf()</a></i>function to read the input file.<p>The description of an individual record is as follows:<code><pre>"&lt;<i>format</i>&gt;", <b>[</b>&lt;<i>arg1</i>&gt;, &lt;<i>arg2</i>&gt;,..., &lt;<i>argn</i>&gt;<b>]</b></code></pre><p>The<i>format</i>is a character string that contains three types ofobjects defined below:<dl compact><dt><i>characters</i><dd><br>Characters that are not<i>escape sequences</i>oras described below, are copied to the output.<dt><i>escape sequences</i><dd><br>Represent non-graphic characters.<dt><i>conversion specifications</i><dd><br>Specifies the output format of each argument.(See below.)</dl><p>The following characters have the following special meaning in theformat string:<dl compact><dt>" " <dd>(An empty character position.)One or moreblankcharacters.<dt><img src="../images/delta.gif" border=0> <dd>Exactly one space character.</dl><p>The notation for spaces allows some flexibility for application output.Note that an empty character position in<i>format</i>represents one or moreblankcharacters on the output (notwhich can includenewline characters).Therefore, another utility that reads that output as its inputmust be prepared to parsethe data using<i><a href="../xsh/scanf.html">scanf()</a></i>,<i><a href="../xcu/awk.html">awk</a></i>,and so forth.<p>The following table lists escape sequences and associated actions on display devices capable of the action.<pre><table  bordercolor=#000000 border=1 align=center><tr valign=top><th align=center><b>Escape Sequence</b><th align=center><b>Represents Character</b><th align=center><b>Terminal Action</b><tr valign=top><td align=center><b>\\</b><td align=left>backslash<td align=left>None.<tr valign=top><td align=center><b>\a</b><td align=left>alert<td align=left> Attempts to alert the user through audible or visible notification. <tr valign=top><td align=center><b>\b</b><td align=left>backspace<td align=left> Moves the printing position to one column before the current position, unless the current position is the start of a line. <tr valign=top><td align=center><b>\f</b><td align=left>form-feed<td align=left> Moves the printing position to the initial printing position of the next logical page. <tr valign=top><td align=center><b>\n</b><td align=left>newline<td align=left> Moves the printing position to the start of the next line. <tr valign=top><td align=center><b>\r</b><td align=left>carriage-return<td align=left> Moves the printing position to the start of the current line. <tr valign=top><td align=center><b>\t</b><td align=left>tab<td align=left> Moves the printing position to the next tab position on the current line. If there are no more tab positions left on the line, the behaviour is undefined. <tr valign=top><td align=center><b>\v</b><td align=left>vertical-tab<td align=left> Moves the printing position to the start of the next vertical tab position. If there are no more vertical tab positions left on the page, the behaviour is undefined. </table></pre><h6 align=center><xref table="Escape Sequences and Associated Actions"><a name="tagt_6">&nbsp;</a></xref>Table: Escape Sequences and Associated Actions</h6><xref type="7" name="escseq"></xref><p>Each conversion specification is introduced bythe percent-sign character (%).After the character %, the following appear in sequence:<dl compact><dt><i>flags</i><dd>Zero or more<i>flags</i>,in any order, that modify the meaning of the conversion specification.<dt><i>field&nbsp;width</i><dd>An optional string of decimal digits tospecify a minimum <i>field width</i>.For an output field,if the converted value has fewerbytes than the field width,it is padded on the left(or right, if the left-adjustmentflag (-), described below, has been given to the field width).<dt><i>precision</i><dd>Gives the minimum number of digits to appearfor the d, o, i, u, x or X conversions(the field is padded with leading zeros), the number ofdigits to appear after the radix character for thee and f conversions, the maximum number of significant digits for theg conversion; or the maximum number ofbytes to be written from a string in s conversion.The precision takes the form of a period (.) followed by adecimal digit string; a null digit string is treated as zero.<dt><i>conversion characters</i><dd><br>A conversion character (see below) that indicates the type of conversionto be applied.</dl><p>The <i>flag</i> characters and their meanings are:<dl compact><dt>-<dd>The result of the conversion is left-justified within the field.<dt>+<dd>The result of a signed conversionalways begins with a sign (+ or -).<dt>&lt;space&gt;<dd>If the first character of a signed conversion is not a sign, aspace characteris prefixed to the result.This means that if thespace character and +flags both appear, thespace characterflag is ignored.<dt>#<dd>The value is to be converted to an alternative form.Forc,d,i,uandsconversions, thebehaviour is undefined.For o conversion, it increases the precision to force thefirst digit of the result to be a zero.For x or X conversion, a non-zero resulthas 0x or 0X prefixed to it,respectively.For e, E, f,g and G conversions,the result always contains a radix character,even if no digitsfollow the radix character.For g and G conversions,trailing zeros are not removed from the result as they usually are.<dt>0<dd>Ford,i,o,u,x,X,e,E,f,gandGconversions, leading zeros (following any indication of sign or base)are used to pad to the field width; no space padding is performed.If the0and-flags both appear, the0flag is ignored.Ford,i,o,u,xandXconversions, if a precision is specified, the0flag is ignored.For other conversions, the behaviour is undefined.</dl><p>Each conversion character results in fetching zero or more arguments.The results are undefined if there are insufficient arguments for the format.If the format is exhausted while arguments remain, the excessarguments are ignored.<p>The<i>conversion characters</i>and their meanings are:<dl compact><dt>d,i,o,u,x,X<dd>The integerargumentis written as signed decimal (d or i),unsigned octal (o), unsigned decimal (u), or unsignedhexadecimal notation (x and X).Thedandispecifiers convert to signed decimal in the style<b>[</b>-<b>]</b><i>dddd</i>.The x conversion uses the numbers and letters0123456789abcdef andthe X conversion uses the numbers and letters0123456789ABCDEF.The <i>precision</i> component of the argumentspecifies the minimum number of digits to appear.If the value being converted can be represented in fewer digitsthan the specified minimum, it is expanded with leading zeros.The default precision is 1.The result of converting a zero value with a precision of 0is no characters.If both the field width and precision are omitted,the implementation may precede, follow or precede and follownumeric argumentsof typesd,ianduwithblank characters;arguments of typeo(octal) may be preceded with leading zeros.The treatment of integers and spaces is different from the<i><a href="../xsh/printf.html">printf()</a></i>function in that they can be surrounded withblank characters.This was done so that, given a format such as:<pre><dl compact><dt> <dd><tt>"%d\n"</tt>, &lt;<i>foo</i>&gt;</dl></pre>the implementation could use a<i><a href="../xsh/printf.html">printf()</a></i>call such as:<code><pre>printf("%6d\n", foo);</code></pre>and still conform.This notation is thus somewhat like<i><a href="../xsh/scanf.html">scanf()</a></i>in addition to<i><a href="../xsh/printf.html">printf()</a></i>.<p><dt>f<dd>The floating point number argument is written in decimal notation inthe style <b>[</b>-<b>]</b><i>ddd</i>.<i>ddd</i>,where the number of digits after the radix character(shown here as a decimal point) is equal tothe <i>precision</i> specification.The LC_NUMERIC locale categorydetermines the radix character to use in this format.If the <i>precision</i> is omitted fromthe argument, six digits are written after the radix character;if the <i>precision</i> is explicitly 0,no radix character appears.<p><dt>e,E<dd>The floating point number argument is written in thestyle <b>[</b>-<b>]</b><i>d</i>.<i>ddd</i>e&plusmn;2dd(the symbol &plumn;indicates either a plus or minus sign),where there is one digit before the radix character(shown here as a decimal point)and the number of digits after it is equal to the precision.The LC_NUMERIC locale categorydetermines the radix character to use in this format.When the precision is missing, six digits are written after the radix character; if theprecision is 0, no radix character appears.The E conversion characterproduces a number with Einstead of e introducing the exponent.The exponent always contains at least two digits.However, if the value to be writtenrequires an exponent greater than two digits,additional exponentdigits are written as necessary.<p><dt>g,G<dd>The floating point number argument is written in style for e (or in style E in the case of a Gconversion character), with the precision specifying the numberof significant digits.The style used depends on the value converted:style g is used only if the exponent resultingfrom the conversion is lessthan -4 or greater than or equal to the precision.Trailing zeros are removed from the result.A radix character appears only if it is followed by a digit.<p><dt>c<dd>The integer argument is converted to an<b>unsigned char</b>and the resulting byte is written.<p><dt>s<dd>The argument is taken to be a stringand bytes fromthe string are written until theend of the stringor the number of bytes indicated by the <i>precision</i>specification of the argument is reached.If the precision is omitted fromthe argument,it is taken to be infinite,so all bytes up to the end of the string are written.<p><dt>%<dd>Write a % character; no argument is converted.<p></dl><p>In no case does a non-existent or insufficient<i>field width</i>cause truncationof a field; if the result of a conversion is wider than the field width,the field is simply expanded to contain the conversion result.The term<i>field width</i>should not be confused with the term<i>precision</i>used in the description of %s.<p>One difference from the C function<i><a href="../xsh/printf.html">printf()</a></i>is that the l and hconversion characters are not used.As expressed by the <b>XCU</b> specification, there is nodifferentiation between decimal values for type<b>int</b>,type <b>long</b>or type <b>short</b>.The specifications %d or %ishould be interpreted as an arbitrary lengthsequence of digits.Also, no distinction is made between single precision and doubleprecision numbers(<b>float</b>or<b>double</b>in C).These are simply referred to as floating point numbers.<p>Many of the output descriptions in the <b>XCU</b> specification use the termsuch as:<pre><dl compact><dt> <dd><tt>"%s"</tt>, &lt;<i>input line</i>&gt;</dl></pre><p>Since the definition of<i>line</i>includes the trailingnewlinecharacter already, there is no need to include a\nin the format; a doublenewline characterwould otherwise result.<p><h5><a name = "tag_006_000_000_001">&nbsp;</a>Examples</h5>To represent the output of a program thatprints a date and time in the form Sunday, July 3, 10:02,where&lt;<i>weekday</i>&gt;and&lt;<i>month</i>&gt;are strings:<p><dl compact><dt> <dd><p><tt>"%s,<img src="../images/delta.gif" border=0>%s<img src="../images/delta.gif" border=0>%d,<img src="../images/delta.gif" border=0>%d:%.2d\n"</tt>, &lt;<i>weekday</i>&gt;,&lt;<i>month</i>&gt;,&lt;<i>day</i>&gt;,&lt;<i>hour</i>&gt;,&lt;<i>min</i>&gt;</p></dl></p><p>To show <sub><img src="../images/pi.gif" border=0></sub>  written to 5 decimal places:<pre><dl compact><dt> <dd><tt>"pi = %.5f\n"</tt>, &lt;<i>value of <sub><img src="../images/pi.gif" border=0></sub></i>&gt;</dl></pre><p>To show an input file format consisting of five colon-separated fields:<p><dl compact><dt> <dd><tt>"%s:%s:%s:%s:%s\n"</tt>, &lt;<i>arg1</i>&gt;,&lt;<i>arg2</i>&gt;,&lt;<i>arg3</i>&gt;,&lt;<i>arg4</i>&gt;,&lt;<i>arg5</i>&gt;</dl></p></blockquote><hr size=2 noshade><center><font size=2>UNIX &reg; is a registered Trademark of The Open Group.<br>Copyright &copy; 1997 The Open Group<br> [ <a href="../index.html">Main Index</a> | <a href="../xshix.html">XSH</a> | <a href="../xcuix.html">XCU</a> | <a href="../xbdix.html">XBD</a> | <a href="../cursesix.html">XCURSES</a> | <a href="../xnsix.html">XNS</a> ]</font></center><hr size=2 noshade></body></html>
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