269 lines
4.6 KiB
HTML
269 lines
4.6 KiB
HTML
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
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<HTML
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><HEAD
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><TITLE
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>The until loop</TITLE
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><META
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NAME="GENERATOR"
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CONTENT="Modular DocBook HTML Stylesheet Version 1.7"><LINK
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REL="HOME"
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TITLE="Bash Guide for Beginners"
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HREF="index.html"><LINK
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REL="UP"
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TITLE="Repetitive tasks"
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HREF="chap_09.html"><LINK
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REL="PREVIOUS"
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TITLE="The while loop"
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HREF="sect_09_02.html"><LINK
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TITLE="I/O redirection and loops"
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HREF="sect_09_04.html"></HEAD
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>Bash Guide for Beginners</TH
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WIDTH="10%"
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ALIGN="left"
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>Prev</A
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WIDTH="80%"
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VALIGN="bottom"
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>Chapter 9. Repetitive tasks</TD
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WIDTH="10%"
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ALIGN="right"
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VALIGN="bottom"
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>Next</A
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><DIV
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CLASS="sect1"
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><H1
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CLASS="sect1"
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><A
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NAME="sect_09_03"
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></A
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>9.3. The until loop</H1
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><DIV
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CLASS="sect2"
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><H2
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CLASS="sect2"
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><A
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NAME="sect_09_03_01"
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></A
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>9.3.1. What is it?</H2
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><P
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>The <B
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CLASS="command"
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>until</B
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> loop is very similar to the <B
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CLASS="command"
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>while</B
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> loop, except that the loop executes until the <B
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CLASS="command"
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>TEST-COMMAND</B
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> executes successfully. As long as this command fails, the loop continues. The syntax is the same as for the <B
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CLASS="command"
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>while</B
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> loop:</P
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><P
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><B
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CLASS="command"
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>until TEST-COMMAND; do CONSEQUENT-COMMANDS; done</B
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> </P
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><P
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>The return status is the exit status of the last command executed in the <B
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CLASS="command"
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>CONSEQUENT-COMMANDS</B
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> list, or zero if none was executed. <B
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CLASS="command"
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>TEST-COMMAND</B
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> can, again, be any command that can exit with a success or failure status, and <B
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CLASS="command"
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>CONSEQUENT-COMMANDS</B
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> can be any UNIX command, script or shell construct.</P
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><P
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>As we already explained previously, the <SPAN
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CLASS="QUOTE"
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>";"</SPAN
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> may be replaced with one or more newlines wherever it appears.</P
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></DIV
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><DIV
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CLASS="sect2"
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><H2
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CLASS="sect2"
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><A
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NAME="sect_09_03_02"
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></A
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>9.3.2. Example</H2
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><P
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>An improved <TT
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CLASS="filename"
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>picturesort.sh</TT
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> script (see <A
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HREF="sect_09_02.html#sect_09_02_02_02"
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>Section 9.2.2.2</A
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>), which tests for available disk space. If not enough disk space is available, remove pictures from the previous months:</P
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><TABLE
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BORDER="0"
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BGCOLOR="#E0E0E0"
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WIDTH="100%"
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><TR
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><TD
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><FONT
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COLOR="#000000"
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><PRE
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CLASS="screen"
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> #!/bin/bash
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# This script copies files from my homedirectory into the webserver directory.
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# A new directory is created every hour.
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# If the pics are taking up too much space, the oldest are removed.
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while true; do
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DISKFUL=$(df -h $WEBDIR | grep -v File | awk '{print $5 }' | cut -d "%" -f1 -)
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until [ $DISKFUL -ge "90" ]; do
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DATE=`date +%Y%m%d`
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HOUR=`date +%H`
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mkdir $WEBDIR/"$DATE"
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while [ $HOUR -ne "00" ]; do
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DESTDIR=$WEBDIR/"$DATE"/"$HOUR"
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mkdir "$DESTDIR"
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mv $PICDIR/*.jpg "$DESTDIR"/
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sleep 3600
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HOUR=`date +%H`
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done
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DISKFULL=$(df -h $WEBDIR | grep -v File | awk '{ print $5 }' | cut -d "%" -f1 -)
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done
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TOREMOVE=$(find $WEBDIR -type d -a -mtime +30)
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for i in $TOREMOVE; do
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rm -rf "$i";
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done
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done
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</PRE
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></FONT
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></TD
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></TR
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></TABLE
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><P
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>Note the initialization of the <TT
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CLASS="varname"
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>HOUR</TT
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> and <TT
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CLASS="varname"
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>DISKFULL</TT
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> variables and the use of options with <B
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CLASS="command"
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>ls</B
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> and <B
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CLASS="command"
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>date</B
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> in order to obtain a correct listing for <TT
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CLASS="varname"
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>TOREMOVE</TT
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>.</P
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></DIV
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></DIV
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><DIV
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CLASS="NAVFOOTER"
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><HR
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ALIGN="LEFT"
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WIDTH="100%"><TABLE
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><TR
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><TD
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WIDTH="33%"
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ALIGN="left"
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VALIGN="top"
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><A
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HREF="sect_09_02.html"
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ACCESSKEY="P"
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>Prev</A
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></TD
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WIDTH="34%"
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ALIGN="center"
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VALIGN="top"
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HREF="index.html"
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>Home</A
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HREF="sect_09_04.html"
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>Next</A
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><TD
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WIDTH="33%"
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ALIGN="left"
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VALIGN="top"
|
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>The while loop</TD
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><TD
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WIDTH="34%"
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ALIGN="center"
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VALIGN="top"
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HREF="chap_09.html"
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>Up</A
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><TD
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WIDTH="33%"
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ALIGN="right"
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VALIGN="top"
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>I/O redirection and loops</TD
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></TR
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></TABLE
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></DIV
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></BODY
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> |