ch34_24.htm

the unix power tools

>N</EM
> command. Same as <EM
CLASS="emphasis"
>p</EM
> if <EM
CLASS="emphasis"
>N</EM
> has 
not been applied to a line.</P
><P
CLASS="para"
><EM
CLASS="emphasis"
>Example</EM
></P
><P
CLASS="para"
>The following script prints each line containing <CODE
CLASS="replaceable"
><I
>word</I
></CODE
>
and also the line before it:</P
><P
CLASS="para"
><BLOCKQUOTE
CLASS="screen"
><PRE
CLASS="screen"
>N
/<CODE
CLASS="replaceable"
><I
>word</I
></CODE
>/P
D</PRE
></BLOCKQUOTE
></P
><P
CLASS="para"
></P
></DD
><DT
CLASS="term"
><CODE
CLASS="literal"
>q</CODE
></DT
><DD
CLASS="listitem"
><P
CLASS="para"
>[<CODE
CLASS="replaceable"
><I
>address</I
></CODE
>]<CODE
CLASS="literal"
>q</CODE
><A
CLASS="indexterm"
NAME="AUTOID-39854"
></A
></P
><P
CLASS="para"
>Quit when <CODE
CLASS="replaceable"
><I
>address</I
></CODE
> is encountered. The addressed line is first
written to output (if default output is not suppressed),
along with any text appended to it by 
previous <EM
CLASS="emphasis"
>a</EM
> or <EM
CLASS="emphasis"
>r</EM
> commands.
See articles <A
CLASS="xref"
HREF="ch34_21.htm"
TITLE="Uses of the sed Quit Command "
>34.21</A
> and
<A
CLASS="xref"
HREF="ch34_22.htm"
TITLE="Dangers of the sed Quit Command "
>34.22</A
>.</P
><P
CLASS="para"
><EM
CLASS="emphasis"
>Example</EM
></P
><P
CLASS="para"
>Delete everything after the addressed line:</P
><P
CLASS="para"
><BLOCKQUOTE
CLASS="screen"
><PRE
CLASS="screen"
>/Garbled text follows:/q</PRE
></BLOCKQUOTE
></P
><P
CLASS="para"
>&#13;Print only the first 50 lines of a file:</P
><P
CLASS="para"
><BLOCKQUOTE
CLASS="screen"
><PRE
CLASS="screen"
>50q</PRE
></BLOCKQUOTE
></P
></DD
><DT
CLASS="term"
><CODE
CLASS="literal"
>r</CODE
></DT
><DD
CLASS="listitem"
><P
CLASS="para"
>[<CODE
CLASS="replaceable"
><I
>address</I
></CODE
>]<CODE
CLASS="literal"
>r </CODE
><CODE
CLASS="replaceable"
><I
>file</I
></CODE
></P
><P
CLASS="para"
>Read contents of <CODE
CLASS="replaceable"
><I
>file</I
></CODE
> and append after the contents of the
pattern space.
Exactly one space must be put between the <CODE
CLASS="literal"
>r</CODE
> and <CODE
CLASS="replaceable"
><I
>file</I
></CODE
>.</P
><P
CLASS="para"
><EM
CLASS="emphasis"
>Example</EM
></P
><P
CLASS="para"
><BLOCKQUOTE
CLASS="screen"
><PRE
CLASS="screen"
>/The list of items follows:/r item_file</PRE
></BLOCKQUOTE
></P
></DD
><DT
CLASS="term"
><CODE
CLASS="literal"
>s</CODE
></DT
><DD
CLASS="listitem"
><P
CLASS="para"
>[<CODE
CLASS="replaceable"
><I
>address1</I
></CODE
>][<CODE
CLASS="literal"
>,</CODE
><CODE
CLASS="replaceable"
><I
>address2</I
></CODE
>]<CODE
CLASS="literal"
>s/</CODE
><CODE
CLASS="replaceable"
><I
>pattern</I
></CODE
><CODE
CLASS="literal"
>/</CODE
><CODE
CLASS="replaceable"
><I
>replacement</I
></CODE
><CODE
CLASS="literal"
>/</CODE
>[<CODE
CLASS="replaceable"
><I
>flags</I
></CODE
>]</P
><P
CLASS="para"
>Substitute <CODE
CLASS="replaceable"
><I
>replacement</I
></CODE
> for <CODE
CLASS="replaceable"
><I
>pattern</I
></CODE
> on each addressed line.
If pattern addresses are used, the pattern <CODE
CLASS="literal"
>//</CODE
> represents the last
pattern address specified.
The following flags can be specified:

<DL
CLASS="variablelist"
><DT
CLASS="term"
><CODE
CLASS="replaceable"
><I
>n</I
></CODE
></DT
><DD
CLASS="listitem"
><P
CLASS="para"
>Replace <CODE
CLASS="replaceable"
><I
>n</I
></CODE
>th instance of <CODE
CLASS="literal"
>/</CODE
><CODE
CLASS="replaceable"
><I
>pattern</I
></CODE
><CODE
CLASS="literal"
>/</CODE
> on each addressed line.
<CODE
CLASS="replaceable"
><I
>n</I
></CODE
> is any number in the range 1 to 512 (default is 1).
See article
<A
CLASS="xref"
HREF="ch34_11.htm"
TITLE="Search &amp; Replacement: One Match Among Many "
>34.11</A
>.</P
></DD
><DT
CLASS="term"
><CODE
CLASS="literal"
>g</CODE
></DT
><DD
CLASS="listitem"
><P
CLASS="para"
>Replace all instances of <CODE
CLASS="literal"
>/</CODE
><CODE
CLASS="replaceable"
><I
>pattern</I
></CODE
><CODE
CLASS="literal"
>/</CODE
> on each addressed line, not
just the first instance.</P
></DD
><DT
CLASS="term"
><CODE
CLASS="literal"
>p</CODE
></DT
><DD
CLASS="listitem"
><P
CLASS="para"
>Print the line if a successful substitution is done. If several
successful substitutions are done, multiple copies of the line will be
printed.
Often used in scripts with the
<SPAN
CLASS="link"
><EM
CLASS="emphasis"
>-n</EM
> command-line option (<A
CLASS="linkend"
HREF="ch34_02.htm"
TITLE="Invoking sed "
>34.2</A
>)</SPAN
>.</P
></DD
><DT
CLASS="term"
><CODE
CLASS="literal"
>w&nbsp;</CODE
><CODE
CLASS="replaceable"
><I
>file</I
></CODE
></DT
><DD
CLASS="listitem"
><P
CLASS="para"
>Write the line to a <CODE
CLASS="replaceable"
><I
>file</I
></CODE
> if a replacement was done. A maximum
of ten different files can be opened in a script.
See articles <A
CLASS="xref"
HREF="ch34_07.htm"
TITLE="Delimiting a Regular Expression "
>34.7</A
> 
through <A
CLASS="xref"
HREF="ch34_10.htm"
TITLE="Referencing Portions of a Search String "
>34.10</A
>.</P
><P
CLASS="para"
><EM
CLASS="emphasis"
>Examples</EM
></P
><P
CLASS="para"
>Here are some short, commented scripts:</P
><P
CLASS="para"
><BLOCKQUOTE
CLASS="screen"
><PRE
CLASS="screen"
># Change third and fourth quote to ( and ):
/function/{
    s/&quot;/)/4
    s/&quot;/(/3
}

# Remove all quotes on a given line:
/Title/s/&quot;//g

# Remove first colon or all quotes; print resulting lines:
s/://p
s/&quot;//gp

# Change first &quot;if&quot; but leave &quot;ifdef&quot; alone:
/ifdef/!s/if/   if/</PRE
></BLOCKQUOTE
></P
><P
CLASS="para"
></P
></DD
></DL
></P
></DD
><DT
CLASS="term"
><CODE
CLASS="literal"
>t</CODE
></DT
><DD
CLASS="listitem"
><P
CLASS="para"
>[<CODE
CLASS="replaceable"
><I
>address1</I
></CODE
>][<CODE
CLASS="literal"
>,</CODE
><CODE
CLASS="replaceable"
><I
>address2</I
></CODE
>]<CODE
CLASS="literal"
>t </CODE
>[<CODE
CLASS="replaceable"
><I
>label</I
></CODE
>]</P
><P
CLASS="para"
>Test if any substitutions have been made on addressed lines,
and if so, branch to line marked by <CODE
CLASS="literal"
>:</CODE
><CODE
CLASS="replaceable"
><I
>label</I
></CODE
>.
(See <EM
CLASS="emphasis"
>b</EM
> and <CODE
CLASS="literal"
>:</CODE
>.) If
<CODE
CLASS="replaceable"
><I
>label</I
></CODE
> is not specified, control falls through to bottom of script.
See article
<A
CLASS="xref"
HREF="ch34_20.htm"
TITLE="The sed Test Command "
>34.20</A
>.</P
><P
CLASS="para"
>The <EM
CLASS="emphasis"
>t</EM
> command can be used like a
<SPAN
CLASS="link"
><EM
CLASS="emphasis"
>case</EM
> statement (<A
CLASS="linkend"
HREF="ch44_05.htm"
TITLE="Test String Values with Bourne Shell case "
>44.5</A
>)</SPAN
>
in the Bourne shell.
You test each case: when it's true, you exit the construct.</P
><P
CLASS="para"
><EM
CLASS="emphasis"
>Example</EM
></P
><P
CLASS="para"
>Suppose you want to fill empty fields of a database. You have this:</P
><P
CLASS="para"
><BLOCKQUOTE
CLASS="screen"
><PRE
CLASS="screen"
>ID: 1   Name: greg   Rate: 45
ID: 2   Name: dale
ID: 3</PRE
></BLOCKQUOTE
></P
><P
CLASS="para"
>You want this:</P
><P
CLASS="para"
><BLOCKQUOTE
CLASS="screen"
><PRE
CLASS="screen"
>ID: 1   Name: greg   Rate: 45   Phone: ??
ID: 2   Name: dale   Rate: ??   Phone: ??
ID: 3   Name: ????   Rate: ??   Phone: ??</PRE
></BLOCKQUOTE
></P
><P
CLASS="para"
>You need to test the number of fields already there.
Here's the script (fields are tab-separated):</P
><P
CLASS="para"
><BLOCKQUOTE
CLASS="screen"
><PRE
CLASS="screen"
>/ID/{
    s/ID: .* Name: .* Rate: .*/&amp;   Phone: ??/p
    t
    s/ID: .* Name: .*/&amp;   Rate: ??   Phone: ??/p
    t
    s/ID: .*/&amp;   Name: ??     Rate: ??   Phone: ??/p
}</PRE
></BLOCKQUOTE
></P
><P
CLASS="para"
></P
></DD
><DT
CLASS="term"
><CODE
CLASS="literal"
>w</CODE
></DT
><DD
CLASS="listitem"
><P
CLASS="para"
>[<CODE
CLASS="replaceable"
><I
>address1</I
></CODE
>][<CODE
CLASS="literal"
>,</CODE
><CODE
CLASS="replaceable"
><I
>address2</I
></CODE
>]<CODE
CLASS="literal"
>w </CODE
><CODE
CLASS="replaceable"
><I
>file</I
></CODE
></P
><P
CLASS="para"
>Append, contents of pattern space to <CODE
CLASS="replaceable"
><I
>file</I
></CODE
>. This action 
occurs when the command is encountered rather than when the pattern space is
output. Exactly one space
must separate the <CODE
CLASS="literal"
>w</CODE
> and <CODE
CLASS="replaceable"
><I
>file</I
></CODE
>.
A maximum of ten different files can be opened in a script.
This command will create the file if it does not exist; if the file
exists, its contents will be overwritten each time the script
is executed. Multiple write commands that direct output to the
same file append to the end of the file.</P
><P
CLASS="para"
><EM
CLASS="emphasis"
>Example</EM
></P
><P
CLASS="para"
><BLOCKQUOTE
CLASS="screen"
><PRE
CLASS="screen"
># Store tbl and eqn blocks in a file:
/^\.TS/,/^\.TE/w troff_stuff
/^\.EQ/,/^\.EN/w troff_stuff</PRE
></BLOCKQUOTE
></P
><P
CLASS="para"
></P
></DD
><DT
CLASS="term"
><CODE
CLASS="literal"
>x</CODE
></DT
><DD
CLASS="listitem"
><P
CLASS="para"
>[<CODE
CLASS="replaceable"
><I
>address1</I
></CODE
>][<CODE
CLASS="literal"
>,</CODE
><CODE
CLASS="replaceable"
><I
>address2</I
></CODE
>]<CODE
CLASS="literal"
>x</CODE
></P
><P
CLASS="para"
>Exchange contents of the pattern space with the contents of the
hold space.
For examples, see <EM
CLASS="emphasis"
>h</EM
> and articles
<A
CLASS="xref"
HREF="ch34_13.htm"
TITLE="Hold Space: The Set-Aside Buffer "
>34.13</A
>
and
<A
CLASS="xref"
HREF="ch34_16.htm"
TITLE="The Deliberate Scrivener "
>34.16</A
>.&#13;</P
></DD
><DT
CLASS="term"
><CODE
CLASS="literal"
>y</CODE
></DT
><DD
CLASS="listitem"
><P
CLASS="para"
>[<CODE
CLASS="replaceable"
><I
>address1</I
></CODE
>][<CODE
CLASS="literal"
>,</CODE
><CODE
CLASS="replaceable"
><I
>address2</I
></CODE
>]<CODE
CLASS="literal"
>y/</CODE
><CODE
CLASS="replaceable"
><I
>abc</I
></CODE
><CODE
CLASS="literal"
>/</CODE
><CODE
CLASS="replaceable"
><I
>xyz</I
></CODE
><CODE
CLASS="literal"
>/</CODE
></P
><P
CLASS="para"
><A
CLASS="indexterm"
NAME="AUTOID-40026"
></A
>Translate characters. Change every instance of <CODE
CLASS="replaceable"
><I
>a</I
></CODE
>
to <CODE
CLASS="replaceable"
><I
>x</I
></CODE
>, <CODE
CLASS="replaceable"
><I
>b</I
></CODE
> to <CODE
CLASS="replaceable"
><I
>y</I
></CODE
>, <CODE
CLASS="replaceable"
><I
>c</I
></CODE
> to <CODE
CLASS="replaceable"
><I
>z</I
></CODE
>, etc.
See articles
<A
CLASS="xref"
HREF="ch34_12.htm"
TITLE="Transformations on Text "
>34.12</A
>
and
<A
CLASS="xref"
HREF="ch34_14.htm"
TITLE="Transforming Part of a Line "
>34.14</A
>.</P
><P
CLASS="para"
><EM
CLASS="emphasis"
>Example</EM
></P
><P
CLASS="para"
><BLOCKQUOTE
CLASS="screen"
><PRE
CLASS="screen"
># Change item 1, 2, 3 to Item A, B, C ...
/^item [1-9]/y/i123456789/IABCDEFGHI/</PRE
></BLOCKQUOTE
></P
></DD
></DL
><A
CLASS="indexterm"
NAME="AUTOID-40041"
></A
><A
CLASS="indexterm"
NAME="AUTOID-40042"
></A
><A
CLASS="indexterm"
NAME="AUTOID-40046"
></A
></DIV
><DIV
CLASS="sect1info"
><P
CLASS="SECT1INFO"
>- <SPAN
CLASS="authorinitials"
>DG</SPAN
> <SPAN
CLASS="bibliomisc"
>from O'Reilly &amp; Associates' <CITE
CLASS="citetitle"
>UNIX in a Nutshell (SVR4/Solaris)</CITE
></SPAN
></P
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