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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"><HTML><HEAD><TITLE>A Sed and Awk Micro-Primer</TITLE><METANAME="GENERATOR"CONTENT="Modular DocBook HTML Stylesheet Version 1.76b+"><LINKREL="HOME"TITLE="Advanced Bash-Scripting Guide"HREF="index.html"><LINKREL="PREVIOUS"TITLE="Reference Cards"HREF="refcards.html"><LINKREL="NEXT"TITLE="Awk"HREF="awk.html"><METAHTTP-EQUIV="Content-Style-Type"CONTENT="text/css"><LINKREL="stylesheet"HREF="common/kde-common.css"TYPE="text/css"><METAHTTP-EQUIV="Content-Type"CONTENT="text/html; charset=iso-8859-1"><METAHTTP-EQUIV="Content-Language"CONTENT="en"><LINKREL="stylesheet"HREF="common/kde-localised.css"TYPE="text/css"TITLE="KDE-English"><LINKREL="stylesheet"HREF="common/kde-default.css"TYPE="text/css"TITLE="KDE-Default"></HEAD><BODYCLASS="APPENDIX"BGCOLOR="#FFFFFF"TEXT="#000000"LINK="#AA0000"VLINK="#AA0055"ALINK="#AA0000"STYLE="font-family: sans-serif;"><DIVCLASS="NAVHEADER"><TABLESUMMARY="Header navigation table"WIDTH="100%"BORDER="0"CELLPADDING="0"CELLSPACING="0"><TR><THCOLSPAN="3"ALIGN="center">Advanced Bash-Scripting Guide: An in-depth exploration of the art of shell scripting</TH></TR><TR><TDWIDTH="10%"ALIGN="left"VALIGN="bottom"><AHREF="refcards.html"ACCESSKEY="P">Prev</A></TD><TDWIDTH="80%"ALIGN="center"VALIGN="bottom"></TD><TDWIDTH="10%"ALIGN="right"VALIGN="bottom"><AHREF="awk.html"ACCESSKEY="N">Next</A></TD></TR></TABLE><HRALIGN="LEFT"WIDTH="100%"></DIV><DIVCLASS="APPENDIX"><H1><ANAME="SEDAWK"></A>Appendix C. A Sed and Awk Micro-Primer</H1><P><ANAME="SEDREF"></A></P><P>This is a very brief introduction to the <BCLASS="COMMAND">sed</B> and <BCLASS="COMMAND">awk</B> text processing utilities. We will deal with only a few basic commands here, but that will suffice for understanding simple sed and awk constructs within shell scripts.</P><P><BCLASS="COMMAND">sed</B>: a non-interactive text file editor</P><P><BCLASS="COMMAND">awk</B>: a field-oriented pattern processing language with a C-style syntax</P><P>For all their differences, the two utilities share a similar invocation syntax, both use <AHREF="regexp.html#REGEXREF">regular expressions </A>, both read input by default from <TTCLASS="FILENAME">stdin</TT>, and both output to <TTCLASS="FILENAME">stdout</TT>. These are well-behaved UNIX tools, and they work together well. The output from one can be piped into the other, and their combined capabilities give shell scripts some of the power of Perl.</P><DIVCLASS="NOTE"><TABLECLASS="NOTE"WIDTH="100%"BORDER="0"><TR><TDWIDTH="25"ALIGN="CENTER"VALIGN="TOP"><IMGSRC="common/note.png"HSPACE="5"ALT="Note"></TD><TDALIGN="LEFT"VALIGN="TOP"><P>One important difference between the utilities is that while shell scripts can easily pass arguments to sed, it is more complicated for awk (see <AHREF="wrapper.html#COLTOTALER">Example 33-5</A> and <AHREF="ivr.html#COLTOTALER2">Example 9-25</A>). </P></TD></TR></TABLE></DIV><DIVCLASS="SECT1"><H1CLASS="SECT1"><ANAME="AEN21068"></A>C.1. Sed</H1><P>Sed is a non-interactive <ANAME="AEN21071"HREF="#FTN.AEN21071">[1]</A> line editor. It receives text input, whether from <TTCLASS="FILENAME">stdin</TT> or from a file, performs certain operations on specified lines of the input, one line at a time, then outputs the result to <TTCLASS="FILENAME">stdout</TT> or to a file. Within a shell script, sed is usually one of several tool components in a pipe.</P><P>Sed determines which lines of its input that it will operate on from the <ICLASS="FIRSTTERM">address range</I> passed to it. <ANAME="AEN21077"HREF="#FTN.AEN21077">[2]</A> Specify this address range either by line number or by a pattern to match. For example, <TTCLASS="REPLACEABLE"><I>3d</I></TT> signals sed to delete line 3 of the input, and <TTCLASS="REPLACEABLE"><I>/windows/d</I></TT> tells sed that you want every line of the input containing a match to <SPANCLASS="QUOTE">"windows"</SPAN> deleted.</P><P>Of all the operations in the sed toolkit, we will focus primarily on the three most commonly used ones. These are <BCLASS="COMMAND">p</B>rinting (to <TTCLASS="FILENAME">stdout</TT>), <BCLASS="COMMAND">d</B>eletion, and <BCLASS="COMMAND">s</B>ubstitution.</P><P><ANAME="SEDBASICTABLE"></A></P><DIVCLASS="TABLE"><HR><ANAME="AEN21090"></A><P><B>Table C-1. Basic sed operators</B></P><TABLEBORDER="1"CLASS="CALSTABLE"><THEAD><TR><THALIGN="LEFT"VALIGN="TOP">Operator</TH><THALIGN="LEFT"VALIGN="TOP">Name</TH><THALIGN="LEFT"VALIGN="TOP">Effect</TH></TR></THEAD><TBODY><TR><TDALIGN="LEFT"VALIGN="TOP"><TTCLASS="OPTION">[address-range]/p</TT></TD><TDALIGN="LEFT"VALIGN="TOP">print</TD><TDALIGN="LEFT"VALIGN="TOP">Print [specified address range]</TD></TR><TR><TDALIGN="LEFT"VALIGN="TOP"><TTCLASS="OPTION">[address-range]/d</TT></TD><TDALIGN="LEFT"VALIGN="TOP">delete</TD><TDALIGN="LEFT"VALIGN="TOP">Delete [specified address range]</TD></TR><TR><TDALIGN="LEFT"VALIGN="TOP"><TTCLASS="OPTION">s/pattern1/pattern2/</TT></TD><TDALIGN="LEFT"VALIGN="TOP">substitute</TD><TDALIGN="LEFT"VALIGN="TOP">Substitute pattern2 for first instance of pattern1 in a line</TD></TR><TR><TDALIGN="LEFT"VALIGN="TOP"><TTCLASS="OPTION">[address-range]/s/pattern1/pattern2/</TT></TD><TDALIGN="LEFT"VALIGN="TOP">substitute</TD><TDALIGN="LEFT"VALIGN="TOP">Substitute pattern2 for first instance of pattern1 in a line, over <TTCLASS="REPLACEABLE"><I>address-range</I></TT></TD></TR><TR><TDALIGN="LEFT"VALIGN="TOP"><TTCLASS="OPTION">[address-range]/y/pattern1/pattern2/</TT></TD><TDALIGN="LEFT"VALIGN="TOP">transform</TD><TDALIGN="LEFT"VALIGN="TOP">replace any character in pattern1 with the corresponding character in pattern2, over <TTCLASS="REPLACEABLE"><I>address-range</I></TT> (equivalent of <BCLASS="COMMAND">tr</B>)</TD></TR><TR><TDALIGN="LEFT"VALIGN="TOP"><TTCLASS="OPTION">g</TT></TD><TDALIGN="LEFT"VALIGN="TOP">global</TD><TDALIGN="LEFT"VALIGN="TOP">Operate on <SPANCLASS="emphasis"><ICLASS="EMPHASIS">every</I></SPAN> pattern match within each matched line of input</TD></TR></TBODY></TABLE><HR></DIV><DIVCLASS="NOTE"><TABLECLASS="NOTE"WIDTH="100%"BORDER="0"><TR><TDWIDTH="25"ALIGN="CENTER"VALIGN="TOP"><IMGSRC="common/note.png"HSPACE="5"ALT="Note"></TD><TDALIGN="LEFT"VALIGN="TOP"><P>Unless the <TTCLASS="OPTION">g</TT> (<ICLASS="FIRSTTERM">global</I>) operator is appended to a <ICLASS="FIRSTTERM">substitute</I> command, the substitution operates only on the first instance of a pattern match within each line.</P></TD></TR></TABLE></DIV><P>From the command line and in a shell script, a sed operation may require quoting and certain options.</P><P><TABLEBORDER="0"BGCOLOR="#E0E0E0"WIDTH="100%"><TR><TD><PRECLASS="PROGRAMLISTING"> 1 sed -e '/^$/d' $filename 2 # The -e option causes the next string to be interpreted as an editing instruction. 3 # (If passing only a single instruction to sed, the "-e" is optional.) 4 # The "strong" quotes ('') protect the RE characters in the instruction 5 #+ from reinterpretation as special characters by the body of the script. 6 # (This reserves RE expansion of the instruction for sed.) 7 # 8 # Operates on the text contained in file $filename.</PRE></TD></TR></TABLE></P><P>In certain cases, a <ICLASS="FIRSTTERM">sed</I> editing command will not work with single quotes.</P><P><TABLEBORDER="0"BGCOLOR="#E0E0E0"WIDTH="100%"><TR><TD><PRECLASS="PROGRAMLISTING"> 1 filename=file1.txt 2 pattern=BEGIN 3 4 sed "/^$pattern/d" "$filename" # Works as specified. 5 # sed '/^$pattern/d' "$filename" has unexpected results. 6 # In this instance, with strong quoting (' ... '), 7 #+ "$pattern" will not expand to "BEGIN".</PRE></TD></TR></TABLE></P><DIVCLASS="NOTE"><TABLECLASS="NOTE"WIDTH="100%"BORDER="0"><TR><TDWIDTH="25"ALIGN="CENTER"VALIGN="TOP"><IMGSRC="common/note.png"HSPACE="5"ALT="Note"></TD><TDALIGN="LEFT"VALIGN="TOP"><P><ICLASS="FIRSTTERM">Sed</I> uses the <TTCLASS="OPTION">-e</TT> option to specify that the following string is an instruction or set of instructions. If there is only a single instruction contained in the string, then this may be omitted.</P></TD></TR></TABLE></DIV><P><TABLEBORDER="0"BGCOLOR="#E0E0E0"WIDTH="100%"><TR><TD><PRECLASS="PROGRAMLISTING"> 1 sed -n '/xzy/p' $filename 2 # The -n option tells sed to print only those lines matching the pattern. 3 # Otherwise all input lines would print. 4 # The -e option not necessary here since there is only a single editing instruction.</PRE></TD></TR></TABLE></P><P><ANAME="SEDOPTABLE"></A></P><DIVCLASS="TABLE"><HR><ANAME="AEN21153"></A><P><B>Table C-2. Examples of sed operators</B></P><TABLEBORDER="1"CLASS="CALSTABLE"><THEAD><TR><THALIGN="LEFT"VALIGN="TOP">Notation</TH><THALIGN="LEFT"VALIGN="TOP">Effect</TH></TR></THEAD><TBODY><TR><TDALIGN="LEFT"VALIGN="TOP"><TTCLASS="OPTION">8d</TT></TD><TDALIGN="LEFT"VALIGN="TOP">Delete 8th line of input.</TD></TR><TR><TDALIGN="LEFT"VALIGN="TOP"><TTCLASS="OPTION">/^$/d</TT></TD><TD⌨️ 快捷键说明
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