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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<HTML
><HEAD
><TITLE
>Complex Commands</TITLE
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><DIV
CLASS="SECT1"
><H1
CLASS="SECT1"
><A
NAME="MOREADV"
></A
>16.2. Complex Commands</H1
><P
></P
><DIV
CLASS="VARIABLELIST"
><P
><B
><A
NAME="CCLISTING1"
></A
>Commands for more advanced users</B
></P
><DL
><DT
><A
NAME="FINDREF"
></A
><B
CLASS="COMMAND"
>find</B
></DT
><DD
><P
><A
NAME="FINDREF0"
></A
></P
><P
>-exec <TT
CLASS="REPLACEABLE"
><I
>COMMAND</I
></TT
> \;</P
><P
>Carries out <TT
CLASS="REPLACEABLE"
><I
>COMMAND</I
></TT
> on
each file that <B
CLASS="COMMAND"
>find</B
> matches. The
command sequence terminates with <SPAN
CLASS="TOKEN"
>;</SPAN
> (the
<SPAN
CLASS="QUOTE"
>";"</SPAN
> is <A
HREF="escapingsection.html#ESCP"
>escaped</A
> to
make certain the shell passes it to <B
CLASS="COMMAND"
>find</B
>
literally, without interpreting it as a special character).</P
><P
> <TABLE
BORDER="1"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><FONT
COLOR="#000000"
><PRE
CLASS="SCREEN"
><TT
CLASS="PROMPT"
>bash$ </TT
><TT
CLASS="USERINPUT"
><B
>find ~/ -name '*.txt'</B
></TT
>
<TT
CLASS="COMPUTEROUTPUT"
>/home/bozo/.kde/share/apps/karm/karmdata.txt
/home/bozo/misc/irmeyc.txt
/home/bozo/test-scripts/1.txt</TT
>
</PRE
></FONT
></TD
></TR
></TABLE
>
</P
><P
><A
NAME="CURLYBRACKETSREF"
></A
></P
><P
>If <TT
CLASS="REPLACEABLE"
><I
>COMMAND</I
></TT
> contains
<SPAN
CLASS="TOKEN"
>{}</SPAN
>, then <B
CLASS="COMMAND"
>find</B
>
substitutes the full path name of the selected file for
<SPAN
CLASS="QUOTE"
>"{}"</SPAN
>.</P
><P
> <TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><FONT
COLOR="#000000"
><PRE
CLASS="PROGRAMLISTING"
>find ~/ -name 'core*' -exec rm {} \;
# Removes all core dump files from user's home directory.</PRE
></FONT
></TD
></TR
></TABLE
>
</P
><P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><FONT
COLOR="#000000"
><PRE
CLASS="PROGRAMLISTING"
>find /home/bozo/projects -mtime -1
# ^ Note minus sign!
# Lists all files in /home/bozo/projects directory tree
#+ that were modified within the last day (current_day - 1).
#
find /home/bozo/projects -mtime 1
# Same as above, but modified *exactly* one day ago.
#
# mtime = last modification time of the target file
# ctime = last status change time (via 'chmod' or otherwise)
# atime = last access time
DIR=/home/bozo/junk_files
find "$DIR" -type f -atime +5 -exec rm {} \;
# ^ ^^
# Curly brackets are placeholder for the path name output by "find."
#
# Deletes all files in "/home/bozo/junk_files"
#+ that have not been accessed in *at least* 5 days (plus sign ... +5).
#
# "-type filetype", where
# f = regular file
# d = directory
# l = symbolic link, etc.
#
# (The 'find' manpage and info page have complete option listings.)</PRE
></FONT
></TD
></TR
></TABLE
>
</P
><P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><FONT
COLOR="#000000"
><PRE
CLASS="PROGRAMLISTING"
>find /etc -exec grep '[0-9][0-9]*[.][0-9][0-9]*[.][0-9][0-9]*[.][0-9][0-9]*' {} \;
# Finds all IP addresses (xxx.xxx.xxx.xxx) in /etc directory files.
# There a few extraneous hits. Can they be filtered out?
# Possibly by:
find /etc -type f -exec cat '{}' \; | tr -c '.[:digit:]' '\n' \
| grep '^[^.][^.]*\.[^.][^.]*\.[^.][^.]*\.[^.][^.]*$'
#
# [:digit:] is one of the character classes
#+ introduced with the POSIX 1003.2 standard.
# Thanks, St<53>phane Chazelas. </PRE
></FONT
></TD
></TR
></TABLE
></P
><DIV
CLASS="NOTE"
><P
></P
><TABLE
CLASS="NOTE"
WIDTH="90%"
BORDER="0"
><TR
><TD
WIDTH="25"
ALIGN="CENTER"
VALIGN="TOP"
><IMG
SRC="../images/note.gif"
HSPACE="5"
ALT="Note"></TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
><P
>The <TT
CLASS="OPTION"
>-exec</TT
> option to
<B
CLASS="COMMAND"
>find</B
> should not be confused with the <A
HREF="internal.html#EXECREF"
>exec</A
> shell builtin.</P
></TD
></TR
></TABLE
></DIV
><DIV
CLASS="EXAMPLE"
><A
NAME="EX57"
></A
><P
><B
>Example 16-3. <I
CLASS="FIRSTTERM"
>Badname</I
>, eliminate file names
in current directory containing bad characters and <A
HREF="special-chars.html#WHITESPACEREF"
>whitespace</A
>.</B
></P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><FONT
COLOR="#000000"
><PRE
CLASS="PROGRAMLISTING"
>#!/bin/bash
# badname.sh
# Delete filenames in current directory containing bad characters.
for filename in *
do
badname=`echo "$filename" | sed -n /[\+\{\;\"\\\=\?~\(\)\&#60;\&#62;\&#38;\*\|\$]/p`
# badname=`echo "$filename" | sed -n '/[+{;"\=?~()&#60;&#62;&#38;*|$]/p'` also works.
# Deletes files containing these nasties: + { ; " \ = ? ~ ( ) &#60; &#62; &#38; * | $
#
rm $badname 2&#62;/dev/null
# ^^^^^^^^^^^ Error messages deep-sixed.
done
# Now, take care of files containing all manner of whitespace.
find . -name "* *" -exec rm -f {} \;
# The path name of the file that _find_ finds replaces the "{}".
# The '\' ensures that the ';' is interpreted literally, as end of command.
exit 0
#---------------------------------------------------------------------
# Commands below this line will not execute because of _exit_ command.
# An alternative to the above script:
find . -name '*[+{;"\\=?~()&#60;&#62;&#38;*|$ ]*' -maxdepth 0 \
-exec rm -f '{}' \;
# The "-maxdepth 0" option ensures that _find_ will not search
#+ subdirectories below $PWD.
# (Thanks, S.C.)</PRE
></FONT
></TD
></TR
></TABLE
></DIV
><DIV
CLASS="EXAMPLE"
><A
NAME="IDELETE"
></A
><P
><B
>Example 16-4. Deleting a file by its <I
CLASS="FIRSTTERM"
>inode</I
>
number</B
></P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><FONT
COLOR="#000000"
><PRE
CLASS="PROGRAMLISTING"
>#!/bin/bash
# idelete.sh: Deleting a file by its inode number.
# This is useful when a filename starts with an illegal character,
#+ such as ? or -.
ARGCOUNT=1 # Filename arg must be passed to script.
E_WRONGARGS=70
E_FILE_NOT_EXIST=71
E_CHANGED_MIND=72
if [ $# -ne "$ARGCOUNT" ]
then
echo "Usage: `basename $0` filename"
exit $E_WRONGARGS
fi
if [ ! -e "$1" ]
then
echo "File \""$1"\" does not exist."
exit $E_FILE_NOT_EXIST
fi
inum=`ls -i | grep "$1" | awk '{print $1}'`
# inum = inode (index node) number of file
# -----------------------------------------------------------------------
# Every file has an inode, a record that holds its physical address info.
# -----------------------------------------------------------------------
echo; echo -n "Are you absolutely sure you want to delete \"$1\" (y/n)? "
# The '-v' option to 'rm' also asks this.
read answer
case "$answer" in
[nN]) echo "Changed your mind, huh?"
exit $E_CHANGED_MIND
;;
*) echo "Deleting file \"$1\".";;
esac
find . -inum $inum -exec rm {} \;
# ^^
# Curly brackets are placeholder
#+ for text output by "find."
echo "File "\"$1"\" deleted!"
exit 0</PRE
></FONT
></TD
></TR
></TABLE
></DIV
><P
>The <B
CLASS="COMMAND"
>find</B
> command also works
without the <TT
CLASS="OPTION"
>-exec</TT
> option.</P
><P
> <TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><FONT
COLOR="#000000"
><PRE
CLASS="PROGRAMLISTING"
>#!/bin/bash
# Find suid root files.
# A strange suid file might indicate a security hole,
#+ or even a system intrusion.
directory="/usr/sbin"
# Might also try /sbin, /bin, /usr/bin, /usr/local/bin, etc.
permissions="+4000" # suid root (dangerous!)
for file in $( find "$directory" -perm "$permissions" )
do
ls -ltF --author "$file"
done</PRE
></FONT
></TD
></TR
></TABLE
>
</P
><P
>See <A
HREF="filearchiv.html#EX48"
>Example 16-30</A
>, <A
HREF="special-chars.html#EX58"
>Example 3-4</A
>,
and <A
HREF="loops1.html#FINDSTRING"
>Example 11-10</A
> for scripts using
<B
CLASS="COMMAND"
>find</B
>. Its <A
HREF="basic.html#MANREF"
>manpage</A
> provides more detail
on this complex and powerful command.</P
></DD
><DT
><A
NAME="XARGSREF"
></A
><B
CLASS="COMMAND"
>xargs</B
></DT
><DD
><P
>A filter for feeding arguments to a command, and also
a tool for assembling the commands themselves. It breaks
a data stream into small enough chunks for filters and
commands to process. Consider it as a powerful replacement
for <A
HREF="commandsub.html#BACKQUOTESREF"
>backquotes</A
>.
In situations where <A
HREF="commandsub.html#COMMANDSUBREF"
>command
substitution</A
> fails with a <SPAN
CLASS="ERRORNAME"
>too
many arguments</SPAN
> error,
substituting <B
CLASS="COMMAND"
>xargs</B
> often
works.
<A
NAME="AEN10465"
HREF="#FTN.AEN10465"
><SPAN
CLASS="footnote"
>[1]</SPAN
></A
>
Normally, <B
CLASS="COMMAND"
>xargs</B
> reads from
<TT
CLASS="FILENAME"
>stdin</TT
> or from a pipe, but it can also
be given the output of a file.</P
><P
>The default command for <B
CLASS="COMMAND"
>xargs</B
> is
<A
HREF="internal.html#ECHOREF"
>echo</A
>. This means that input
piped to <B
CLASS="COMMAND"
>xargs</B
> may have linefeeds and
other whitespace characters stripped out.</P
><P
> <TABLE
BORDER="1"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><FONT
COLOR="#000000"
><PRE
CLASS="SCREEN"
><TT
CLASS="PROMPT"
>bash$ </TT
><TT
CLASS="USERINPUT"
><B
>ls -l</B
></TT
>
<TT
CLASS="COMPUTEROUTPUT"
>total 0
-rw-rw-r-- 1 bozo bozo 0 Jan 29 23:58 file1
-rw-rw-r-- 1 bozo bozo 0 Jan 29 23:58 file2</TT
>
<TT
CLASS="PROMPT"
>bash$ </TT
><TT
CLASS="USERINPUT"
><B
>ls -l | xargs</B
></TT
>
<TT
CLASS="COMPUTEROUTPUT"
>total 0 -rw-rw-r-- 1 bozo bozo 0 Jan 29 23:58 file1 -rw-rw-r-- 1 bozo bozo 0 Jan...</TT
>
<TT
CLASS="PROMPT"
>bash$ </TT
><TT
CLASS="USERINPUT"
><B
>find ~/mail -type f | xargs grep "Linux"</B
></TT
>
<TT
CLASS="COMPUTEROUTPUT"
>./misc:User-Agent: slrn/0.9.8.1 (Linux)
./sent-mail-jul-2005: hosted by the Linux Documentation Project.
./sent-mail-jul-2005: (Linux Documentation Project Site, rtf version)
./sent-mail-jul-2005: Subject: Criticism of Bozo's Windows/Linux article
./sent-mail-jul-2005: while mentioning that the Linux ext2/ext3 filesystem
. . .</TT
>
</PRE
></FONT
></TD
></TR
></TABLE
>
</P
><P
><TT
CLASS="USERINPUT"
><B
>ls | xargs -p -l gzip</B
></TT
> <A
HREF="filearchiv.html#GZIPREF"
>gzips</A
> every file in current
directory, one at a time, prompting before each
operation.</P
><P
><A
NAME="XARGSONEATATIME"
></A
></P
><DIV
CLASS="NOTE"
><P
></P
><TABLE
CLASS="NOTE"
WIDTH="90%"
BORDER="0"
><TR
><TD
WIDTH="25"
ALIGN="CENTER"
VALIGN="TOP"
><IMG
SRC="../images/note.gif"
HSPACE="5"
ALT="Note"></TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
><P
>Note that <I
CLASS="FIRSTTERM"
>xargs</I
> processes the
arguments passed to it sequentially, <EM
>one at
a time</EM
>.</P
><P
><TABLE
BORDER="1"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><FONT
COLOR="#000000"
><PRE
CLASS="SCREEN"
><TT
CLASS="PROMPT"
>bash$ </TT
><TT
CLASS="USERINPUT"
><B
>find /usr/bin | xargs file</B
></TT
>
<TT
CLASS="COMPUTEROUTPUT"
>/usr/bin: directory
/usr/bin/foomatic-ppd-options: perl script text executable
. . .</TT
>
</PRE
></FONT
></TD
></TR
></TABLE
>
</P
></TD
></TR
></TABLE
></DIV
><P
><A
NAME="XARGSLIMARGS"
></A
></P
><DIV
CLASS="TIP"
><P
></P
><TABLE
CLASS="TIP"
WIDTH="90%"
BORDER="0"
><TR
><TD
WIDTH="25"
ALIGN="CENTER"
VALIGN="TOP"
><IMG
SRC="../images/tip.gif"
HSPACE="5"
ALT="Tip"></TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
><P
>An interesting <I
CLASS="FIRSTTERM"
>xargs</I
>
option is <TT
CLASS="OPTION"
>-n <TT
CLASS="REPLACEABLE"
><I
>NN</I
></TT
></TT
>,
which limits to <TT
CLASS="REPLACEABLE"
><I
>NN</I
></TT
> the number
of arguments passed.</P
><P
><TT
CLASS="USERINPUT"
><B
>ls | xargs -n 8 echo</B
></TT
> lists the files in the
current directory in <TT
CLASS="LITERAL"
>8</TT
> columns.</P
></TD
></TR
></TABLE
></DIV
><P
><A
NAME="XARGSWS"
></A
></P
><DIV
CLASS="TIP"
><P
></P
><TABLE
CLASS="TIP"
WIDTH="90%"
BORDER="0"
><TR
><TD
WIDTH="25"
ALIGN="CENTER"
VALIGN="TOP"
><IMG
SRC="../images/tip.gif"
HSPACE="5"
ALT="Tip"></TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
><P
>Another useful option is
<TT
CLASS="OPTION"
>-0</TT
>, in combination with <TT
CLASS="USERINPUT"
><B
>find
-print0</B
></TT
> or <TT
CLASS="USERINPUT"
><B
>grep -lZ</B
></TT
>. This
allows handling arguments containing whitespace or
quotes.</P
><P
> <TT
CLASS="USERINPUT"
><B
>find / -type f -print0 | xargs -0 grep -liwZ GUI | xargs -0 rm -f</B
></TT
>
</P
><P
> <TT
CLASS="USERINPUT"
><B
>grep -rliwZ GUI / | xargs -0 rm -f</B
></TT
>
</P
><P
>Either of the above will remove any file containing <SPAN
CLASS="QUOTE"
>"GUI"</SPAN
>.
<EM
>(Thanks, S.C.)</EM
></P
><P
>Or:
<TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><FONT
COLOR="#000000"
><PRE
CLASS="PROGRAMLISTING"
>cat /proc/"$pid"/"$OPTION" | xargs -0 echo
# Formats output: ^^^^^^^^^^^^^^^
# From Han Holl's fixup of "get-commandline.sh"
#+ script in "/dev and /proc" chapter.</PRE
></FONT
></TD
></TR
></TABLE
></P
></TD
></TR
></TABLE
></DIV
><DIV
CLASS="TIP"
><P
></P
><TABLE
CLASS="TIP"
WIDTH="90%"
BORDER="0"
><TR
><TD
WIDTH="25"
ALIGN="CENTER"
VALIGN="TOP"
><IMG
SRC="../images/tip.gif"
HSPACE="5"
ALT="Tip"></TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
><P
><A
NAME="XARGSMULTIPROCESS"
></A
></P
><P
>The <TT
CLASS="OPTION"
>-P</TT
> option to
<I
CLASS="FIRSTTERM"
>xargs</I
> permits running
processes in parallel. This speeds up execution
in a machine with a multicore CPU.</P
><P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><FONT
COLOR="#000000"
><PRE
CLASS="PROGRAMLISTING"
>#!/bin/bash
ls *gif | xargs -t -n1 -P2 gif2png
# Converts all the gif images in current directory to png.
# Options:
# =======
# -t Print command to stderr.
# -n1 At most 1 argument per command line.
# -P2 Run up to 2 processes simultaneously.
# Thank you, Roberto Polli, for the inspiration.</PRE
></FONT
></TD
></TR
></TABLE
></P
></TD
></TR
></TABLE
></DIV
><DIV
CLASS="EXAMPLE"
><A
NAME="EX41"
></A
><P
><B
>Example 16-5. Logfile: Using <I
CLASS="FIRSTTERM"
>xargs</I
> to monitor system log</B
></P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><FONT
COLOR="#000000"
><PRE
CLASS="PROGRAMLISTING"
>#!/bin/bash
# Generates a log file in current directory
# from the tail end of /var/log/messages.
# Note: /var/log/messages must be world readable
# if this script invoked by an ordinary user.
# #root chmod 644 /var/log/messages
LINES=5
( date; uname -a ) &#62;&#62;logfile
# Time and machine name
echo ---------------------------------------------------------- &#62;&#62;logfile
tail -n $LINES /var/log/messages | xargs | fmt -s &#62;&#62;logfile
echo &#62;&#62;logfile
echo &#62;&#62;logfile
exit 0
# Note:
# ----
# As Frank Wang points out,
#+ unmatched quotes (either single or double quotes) in the source file
#+ may give xargs indigestion.
#
# He suggests the following substitution for line 15:
# tail -n $LINES /var/log/messages | tr -d "\"'" | xargs | fmt -s &#62;&#62;logfile
# Exercise:
# --------
# Modify this script to track changes in /var/log/messages at intervals
#+ of 20 minutes.
# Hint: Use the "watch" command. </PRE
></FONT
></TD
></TR
></TABLE
></DIV
><P
><A
NAME="XARGSCURLYREF"
></A
></P
><P
><A
HREF="moreadv.html#CURLYBRACKETSREF"
>As in
<B
CLASS="COMMAND"
>find</B
></A
>, a curly bracket
pair serves as a placeholder for replacement text.</P
><DIV
CLASS="EXAMPLE"
><A
NAME="EX42"
></A
><P
><B
>Example 16-6. Copying files in current directory to another</B
></P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><FONT
COLOR="#000000"
><PRE
CLASS="PROGRAMLISTING"
>#!/bin/bash
# copydir.sh
# Copy (verbose) all files in current directory ($PWD)
#+ to directory specified on command-line.
E_NOARGS=85
if [ -z "$1" ] # Exit if no argument given.
then
echo "Usage: `basename $0` directory-to-copy-to"
exit $E_NOARGS
fi
ls . | xargs -i -t cp ./{} $1
# ^^ ^^ ^^
# -t is "verbose" (output command-line to stderr) option.
# -i is "replace strings" option.
# {} is a placeholder for output text.
# This is similar to the use of a curly-bracket pair in "find."
#
# List the files in current directory (ls .),
#+ pass the output of "ls" as arguments to "xargs" (-i -t options),
#+ then copy (cp) these arguments ({}) to new directory ($1).
#
# The net result is the exact equivalent of
#+ cp * $1
#+ unless any of the filenames has embedded "whitespace" characters.
exit 0</PRE
></FONT
></TD
></TR
></TABLE
></DIV
><DIV
CLASS="EXAMPLE"
><A
NAME="KILLBYNAME"
></A
><P
><B
>Example 16-7. Killing processes by name</B
></P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><FONT
COLOR="#000000"
><PRE
CLASS="PROGRAMLISTING"
>#!/bin/bash
# kill-byname.sh: Killing processes by name.
# Compare this script with kill-process.sh.
# For instance,
#+ try "./kill-byname.sh xterm" --
#+ and watch all the xterms on your desktop disappear.
# Warning:
# -------
# This is a fairly dangerous script.
# Running it carelessly (especially as root)
#+ can cause data loss and other undesirable effects.
E_BADARGS=66
if test -z "$1" # No command-line arg supplied?
then
echo "Usage: `basename $0` Process(es)_to_kill"
exit $E_BADARGS
fi
PROCESS_NAME="$1"
ps ax | grep "$PROCESS_NAME" | awk '{print $1}' | xargs -i kill {} 2&#38;&#62;/dev/null
# ^^ ^^
# ---------------------------------------------------------------
# Notes:
# -i is the "replace strings" option to xargs.
# The curly brackets are the placeholder for the replacement.
# 2&#38;&#62;/dev/null suppresses unwanted error messages.
#
# Can grep "$PROCESS_NAME" be replaced by pidof "$PROCESS_NAME"?
# ---------------------------------------------------------------
exit $?
# The "killall" command has the same effect as this script,
#+ but using it is not quite as educational.</PRE
></FONT
></TD
></TR
></TABLE
></DIV
><DIV
CLASS="EXAMPLE"
><A
NAME="WF2"
></A
><P
><B
>Example 16-8. Word frequency analysis using
<I
CLASS="FIRSTTERM"
>xargs</I
></B
></P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><FONT
COLOR="#000000"
><PRE
CLASS="PROGRAMLISTING"
>#!/bin/bash
# wf2.sh: Crude word frequency analysis on a text file.
# Uses 'xargs' to decompose lines of text into single words.
# Compare this example to the "wf.sh" script later on.
# Check for input file on command-line.
ARGS=1
E_BADARGS=85
E_NOFILE=86
if [ $# -ne "$ARGS" ]
# Correct number of arguments passed to script?
then
echo "Usage: `basename $0` filename"
exit $E_BADARGS
fi
if [ ! -f "$1" ] # Does file exist?
then
echo "File \"$1\" does not exist."
exit $E_NOFILE
fi
#####################################################
cat "$1" | xargs -n1 | \
# List the file, one word per line.
tr A-Z a-z | \
# Shift characters to lowercase.
sed -e 's/\.//g' -e 's/\,//g' -e 's/ /\
/g' | \
# Filter out periods and commas, and
#+ change space between words to linefeed,
sort | uniq -c | sort -nr
# Finally remove duplicates, prefix occurrence count
#+ and sort numerically.
#####################################################
# This does the same job as the "wf.sh" example,
#+ but a bit more ponderously, and it runs more slowly (why?).
exit $?</PRE
></FONT
></TD
></TR
></TABLE
></DIV
></DD
><DT
><A
NAME="EXPRREF"
></A
><TT
CLASS="USERINPUT"
><B
>expr</B
></TT
></DT
><DD
><P
>All-purpose expression evaluator:
Concatenates and evaluates the arguments according
to the operation given (arguments must be separated
by spaces). Operations may be arithmetic, comparison,
string, or logical.</P
><P
></P
><DIV
CLASS="VARIABLELIST"
><DL
><DT
><TT
CLASS="USERINPUT"
><B
>expr 3 + 5</B
></TT
></DT
><DD
><P
>returns <TT
CLASS="LITERAL"
>8</TT
></P
></DD
><DT
><TT
CLASS="USERINPUT"
><B
>expr 5 % 3</B
></TT
></DT
><DD
><P
>returns 2</P
></DD
><DT
><TT
CLASS="USERINPUT"
><B
>expr 1 / 0</B
></TT
></DT
><DD
><P
>returns the error message, <SPAN
CLASS="ERRORCODE"
>expr: division by
zero</SPAN
></P
><P
>Illegal arithmetic operations not allowed.</P
></DD
><DT
><TT
CLASS="USERINPUT"
><B
>expr 5 \* 3</B
></TT
></DT
><DD
><P
>returns 15</P
><P
>The multiplication operator
must be escaped when used in an arithmetic expression
with <B
CLASS="COMMAND"
>expr</B
>.</P
></DD
><DT
><TT
CLASS="USERINPUT"
><B
>y=`expr $y + 1`</B
></TT
></DT
><DD
><P
>Increment a variable, with the same effect
as <TT
CLASS="USERINPUT"
><B
>let y=y+1</B
></TT
> and
<TT
CLASS="USERINPUT"
><B
>y=$(($y+1))</B
></TT
>. This is an
example of <A
HREF="arithexp.html#ARITHEXPREF"
>arithmetic
expansion</A
>.</P
></DD
><DT
><A
NAME="EXPEXTRSUB"
></A
><TT
CLASS="USERINPUT"
><B
>z=`expr substr
$string $position $length`</B
></TT
></DT
><DD
><P
>Extract substring of $length characters, starting
at $position.</P
></DD
></DL
></DIV
><DIV
CLASS="EXAMPLE"
><A
NAME="EX45"
></A
><P
><B
>Example 16-9. Using <I
CLASS="FIRSTTERM"
>expr</I
></B
></P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><FONT
COLOR="#000000"
><PRE
CLASS="PROGRAMLISTING"
>#!/bin/bash
# Demonstrating some of the uses of 'expr'
# =======================================
echo
# Arithmetic Operators
# ---------- ---------
echo "Arithmetic Operators"
echo
a=`expr 5 + 3`
echo "5 + 3 = $a"
a=`expr $a + 1`
echo
echo "a + 1 = $a"
echo "(incrementing a variable)"
a=`expr 5 % 3`
# modulo
echo
echo "5 mod 3 = $a"
echo
echo
# Logical Operators
# ------- ---------
# Returns 1 if true, 0 if false,
#+ opposite of normal Bash convention.
echo "Logical Operators"
echo
x=24
y=25
b=`expr $x = $y` # Test equality.
echo "b = $b" # 0 ( $x -ne $y )
echo
a=3
b=`expr $a \&#62; 10`
echo 'b=`expr $a \&#62; 10`, therefore...'
echo "If a &#62; 10, b = 0 (false)"
echo "b = $b" # 0 ( 3 ! -gt 10 )
echo
b=`expr $a \&#60; 10`
echo "If a &#60; 10, b = 1 (true)"
echo "b = $b" # 1 ( 3 -lt 10 )
echo
# Note escaping of operators.
b=`expr $a \&#60;= 3`
echo "If a &#60;= 3, b = 1 (true)"
echo "b = $b" # 1 ( 3 -le 3 )
# There is also a "\&#62;=" operator (greater than or equal to).
echo
echo
# String Operators
# ------ ---------
echo "String Operators"
echo
a=1234zipper43231
echo "The string being operated upon is \"$a\"."
# length: length of string
b=`expr length $a`
echo "Length of \"$a\" is $b."
# index: position of first character in substring
# that matches a character in string
b=`expr index $a 23`
echo "Numerical position of first \"2\" in \"$a\" is \"$b\"."
# substr: extract substring, starting position &#38; length specified
b=`expr substr $a 2 6`
echo "Substring of \"$a\", starting at position 2,\
and 6 chars long is \"$b\"."
# The default behavior of the 'match' operations is to
#+ search for the specified match at the BEGINNING of the string.
#
# Using Regular Expressions ...
b=`expr match "$a" '[0-9]*'` # Numerical count.
echo Number of digits at the beginning of \"$a\" is $b.
b=`expr match "$a" '\([0-9]*\)'` # Note that escaped parentheses
# == == #+ trigger substring match.
echo "The digits at the beginning of \"$a\" are \"$b\"."
echo
exit 0</PRE
></FONT
></TD
></TR
></TABLE
></DIV
><DIV
CLASS="IMPORTANT"
><P
></P
><TABLE
CLASS="IMPORTANT"
WIDTH="90%"
BORDER="0"
><TR
><TD
WIDTH="25"
ALIGN="CENTER"
VALIGN="TOP"
><IMG
SRC="../images/important.gif"
HSPACE="5"
ALT="Important"></TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
><P
>The <A
HREF="special-chars.html#NULLREF"
>:
(<I
CLASS="FIRSTTERM"
>null</I
>)</A
> operator
can substitute for <B
CLASS="COMMAND"
>match</B
>. For example,
<TT
CLASS="USERINPUT"
><B
>b=`expr $a : [0-9]*`</B
></TT
> is the
exact equivalent of <TT
CLASS="USERINPUT"
><B
>b=`expr match $a
[0-9]*`</B
></TT
> in the above listing.</P
><P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><FONT
COLOR="#000000"
><PRE
CLASS="PROGRAMLISTING"
>#!/bin/bash
echo
echo "String operations using \"expr \$string : \" construct"
echo "==================================================="
echo
a=1234zipper5FLIPPER43231
echo "The string being operated upon is \"`expr "$a" : '\(.*\)'`\"."
# Escaped parentheses grouping operator. == ==
# ***************************
#+ Escaped parentheses
#+ match a substring
# ***************************
# If no escaped parentheses ...
#+ then 'expr' converts the string operand to an integer.
echo "Length of \"$a\" is `expr "$a" : '.*'`." # Length of string
echo "Number of digits at the beginning of \"$a\" is `expr "$a" : '[0-9]*'`."
# ------------------------------------------------------------------------- #
echo
echo "The digits at the beginning of \"$a\" are `expr "$a" : '\([0-9]*\)'`."
# == ==
echo "The first 7 characters of \"$a\" are `expr "$a" : '\(.......\)'`."
# ===== == ==
# Again, escaped parentheses force a substring match.
#
echo "The last 7 characters of \"$a\" are `expr "$a" : '.*\(.......\)'`."
# ==== end of string operator ^^
# (In fact, means skip over one or more of any characters until specified
#+ substring found.)
echo
exit 0</PRE
></FONT
></TD
></TR
></TABLE
></P
></TD
></TR
></TABLE
></DIV
></DD
></DL
></DIV
><P
>The above script illustrates how
<B
CLASS="COMMAND"
>expr</B
> uses the <I
CLASS="FIRSTTERM"
>escaped
parentheses -- \( ... \) --</I
> grouping operator
in tandem with <A
HREF="regexp.html#REGEXREF"
>regular
expression</A
> parsing to match a substring.
Here is a another example, this time from <SPAN
CLASS="QUOTE"
>"real
life."</SPAN
>
<TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><FONT
COLOR="#000000"
><PRE
CLASS="PROGRAMLISTING"
># Strip the whitespace from the beginning and end.
LRFDATE=`expr "$LRFDATE" : '[[:space:]]*\(.*\)[[:space:]]*$'`
# From Peter Knowles' "booklistgen.sh" script
#+ for converting files to Sony Librie/PRS-50X format.
# (http://booklistgensh.peterknowles.com)</PRE
></FONT
></TD
></TR
></TABLE
>
</P
><P
><A
HREF="wrapper.html#PERLREF"
>Perl</A
>,
<A
HREF="sedawk.html#SEDREF"
>sed</A
>, and <A
HREF="awk.html#AWKREF"
>awk</A
> have far superior string
parsing facilities. A short <B
CLASS="COMMAND"
>sed</B
> or
<B
CLASS="COMMAND"
>awk</B
> <SPAN
CLASS="QUOTE"
>"subroutine"</SPAN
> within
a script (see <A
HREF="wrapper.html"
>Section 36.2</A
>) is an attractive
alternative to <B
CLASS="COMMAND"
>expr</B
>.</P
><P
>See <A
HREF="string-manipulation.html"
>Section 10.1</A
> for more on
using <B
CLASS="COMMAND"
>expr</B
> in string operations.</P
></DIV
><H3
CLASS="FOOTNOTES"
>Notes</H3
><TABLE
BORDER="0"
CLASS="FOOTNOTES"
WIDTH="100%"
><TR
><TD
ALIGN="LEFT"
VALIGN="TOP"
WIDTH="5%"
><A
NAME="FTN.AEN10465"
HREF="moreadv.html#AEN10465"
><SPAN
CLASS="footnote"
>[1]</SPAN
></A
></TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
WIDTH="95%"
><P
>And even when <I
CLASS="FIRSTTERM"
>xargs</I
> is
not strictly necessary, it can speed up execution of a command
involving <A
HREF="timedate.html#BATCHPROCREF"
>batch-processing</A
> of multiple
files.</P
></TD
></TR
></TABLE
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CLASS="NAVFOOTER"
><HR
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><A
HREF="basic.html"
ACCESSKEY="P"
>Prev</A
></TD
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ACCESSKEY="H"
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><A
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></TD
></TR
><TR
><TD
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><TD
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VALIGN="top"
><A
HREF="external.html"
ACCESSKEY="U"
>Up</A
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