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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<HTML
><HEAD
><TITLE
>Manipulating Strings</TITLE
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>Advanced Bash-Scripting Guide: </TH
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WIDTH="80%"
ALIGN="center"
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>Chapter 10. Manipulating Variables</TD
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><A
HREF="parameter-substitution.html"
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>Next</A
></TD
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><HR
ALIGN="LEFT"
WIDTH="100%"></DIV
><DIV
CLASS="SECT1"
><H1
CLASS="SECT1"
><A
NAME="STRING-MANIPULATION"
></A
>10.1. Manipulating Strings</H1
><P
><A
NAME="STRINGMANIP"
></A
></P
><P
>Bash supports a surprising number of string manipulation
operations. Unfortunately, these tools lack
a unified focus. Some are a subset of <A
HREF="parameter-substitution.html#PARAMSUBREF"
>parameter substitution</A
>, and
others fall under the functionality of the UNIX <A
HREF="moreadv.html#EXPRREF"
>expr</A
> command. This results in
inconsistent command syntax and overlap of functionality,
not to mention confusion.</P
><P
></P
><DIV
CLASS="VARIABLELIST"
><P
><B
>String Length</B
></P
><DL
><DT
>${#string}</DT
><DD
><P
></P
></DD
><DT
>expr length $string</DT
><DD
><P
><A
NAME="STRLEN"
></A
>These are the equivalent of
<I
CLASS="FIRSTTERM"
>strlen()</I
> in
<I
CLASS="FIRSTTERM"
>C</I
>.</P
></DD
><DT
>expr "$string" : '.*'</DT
><DD
><P
> <TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><FONT
COLOR="#000000"
><PRE
CLASS="PROGRAMLISTING"
>stringZ=abcABC123ABCabc
echo ${#stringZ} # 15
echo `expr length $stringZ` # 15
echo `expr "$stringZ" : '.*'` # 15</PRE
></FONT
></TD
></TR
></TABLE
>
</P
></DD
></DL
></DIV
><DIV
CLASS="EXAMPLE"
><A
NAME="PARAGRAPHSPACE"
></A
><P
><B
>Example 10-1. Inserting a blank line between paragraphs in a text file</B
></P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><FONT
COLOR="#000000"
><PRE
CLASS="PROGRAMLISTING"
>#!/bin/bash
# paragraph-space.sh
# Ver. 2.1, Reldate 29Jul12 [fixup]
# Inserts a blank line between paragraphs of a single-spaced text file.
# Usage: $0 &#60;FILENAME
MINLEN=60 # Change this value? It's a judgment call.
# Assume lines shorter than $MINLEN characters ending in a period
#+ terminate a paragraph. See exercises below.
while read line # For as many lines as the input file has ...
do
echo "$line" # Output the line itself.
len=${#line}
if [[ "$len" -lt "$MINLEN" &#38;&#38; "$line" =~ [*{\.}]$ ]]
# if [[ "$len" -lt "$MINLEN" &#38;&#38; "$line" =~ \[*\.\] ]]
# An update to Bash broke the previous version of this script. Ouch!
# Thank you, Halim Srama, for pointing this out and suggesting a fix.
then echo # Add a blank line immediately
fi #+ after a short line terminated by a period.
done
exit
# Exercises:
# ---------
# 1) The script usually inserts a blank line at the end
#+ of the target file. Fix this.
# 2) Line 17 only considers periods as sentence terminators.
# Modify this to include other common end-of-sentence characters,
#+ such as ?, !, and ".</PRE
></FONT
></TD
></TR
></TABLE
></DIV
><P
></P
><DIV
CLASS="VARIABLELIST"
><P
><B
>Length of Matching Substring at Beginning of String</B
></P
><DL
><DT
><A
NAME="EXPRMATCH"
></A
>expr match "$string"
'$substring'</DT
><DD
><P
><TT
CLASS="REPLACEABLE"
><I
>$substring</I
></TT
> is a <A
HREF="regexp.html#REGEXREF"
>regular expression</A
>.</P
></DD
><DT
>expr "$string" : '$substring'</DT
><DD
><P
><TT
CLASS="REPLACEABLE"
><I
>$substring</I
></TT
> is a regular
expression.</P
><P
>&#13; <TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><FONT
COLOR="#000000"
><PRE
CLASS="PROGRAMLISTING"
>stringZ=abcABC123ABCabc
# |------|
# 12345678
echo `expr match "$stringZ" 'abc[A-Z]*.2'` # 8
echo `expr "$stringZ" : 'abc[A-Z]*.2'` # 8</PRE
></FONT
></TD
></TR
></TABLE
>
</P
></DD
></DL
></DIV
><P
></P
><DIV
CLASS="VARIABLELIST"
><P
><B
>Index</B
></P
><DL
><DT
><A
NAME="SUBSTRINGINDEX2"
></A
>expr index $string
$substring</DT
><DD
><P
>Numerical position in $string of first character in
$substring that matches.</P
><P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><FONT
COLOR="#000000"
><PRE
CLASS="PROGRAMLISTING"
>stringZ=abcABC123ABCabc
# 123456 ...
echo `expr index "$stringZ" C12` # 6
# C position.
echo `expr index "$stringZ" 1c` # 3
# 'c' (in #3 position) matches before '1'.</PRE
></FONT
></TD
></TR
></TABLE
></P
><P
>This is the near equivalent of
<I
CLASS="FIRSTTERM"
>strchr()</I
> in
<I
CLASS="FIRSTTERM"
>C</I
>.</P
></DD
></DL
></DIV
><P
></P
><DIV
CLASS="VARIABLELIST"
><P
><B
>Substring Extraction</B
></P
><DL
><DT
><A
NAME="SUBSTREXTR01"
></A
>${string:position}</DT
><DD
><P
>Extracts substring from <TT
CLASS="REPLACEABLE"
><I
>$string</I
></TT
> at
<TT
CLASS="REPLACEABLE"
><I
>$position</I
></TT
>.</P
><P
>If the <TT
CLASS="VARNAME"
>$string</TT
> parameter is
<SPAN
CLASS="QUOTE"
>"<SPAN
CLASS="TOKEN"
>*</SPAN
>"</SPAN
>
or <SPAN
CLASS="QUOTE"
>"<SPAN
CLASS="TOKEN"
>@</SPAN
>"</SPAN
>, then this extracts the
<A
HREF="internalvariables.html#POSPARAMREF"
>positional parameters</A
>,
<A
NAME="AEN5987"
HREF="#FTN.AEN5987"
><SPAN
CLASS="footnote"
>[1]</SPAN
></A
>
starting at <TT
CLASS="VARNAME"
>$position</TT
>.</P
></DD
><DT
><A
NAME="SUBSTREXTR02"
></A
>${string:position:length}</DT
><DD
><P
>Extracts <TT
CLASS="REPLACEABLE"
><I
>$length</I
></TT
> characters
of substring from <TT
CLASS="REPLACEABLE"
><I
>$string</I
></TT
> at
<TT
CLASS="REPLACEABLE"
><I
>$position</I
></TT
>.</P
><P
> <TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><FONT
COLOR="#000000"
><PRE
CLASS="PROGRAMLISTING"
>stringZ=abcABC123ABCabc
# 0123456789.....
# 0-based indexing.
echo ${stringZ:0} # abcABC123ABCabc
echo ${stringZ:1} # bcABC123ABCabc
echo ${stringZ:7} # 23ABCabc
echo ${stringZ:7:3} # 23A
# Three characters of substring.
# Is it possible to index from the right end of the string?
echo ${stringZ:-4} # abcABC123ABCabc
# Defaults to full string, as in ${parameter:-default}.
# However . . .
echo ${stringZ:(-4)} # Cabc
echo ${stringZ: -4} # Cabc
# Now, it works.
# Parentheses or added space "escape" the position parameter.
# Thank you, Dan Jacobson, for pointing this out.</PRE
></FONT
></TD
></TR
></TABLE
>
</P
><P
>The <I
CLASS="FIRSTTERM"
>position</I
> and
<I
CLASS="FIRSTTERM"
>length</I
> arguments can be
<SPAN
CLASS="QUOTE"
>"parameterized,"</SPAN
> that is, represented as a
variable, rather than as a numerical constant.</P
><P
><A
NAME="RANDSTRING0"
></A
></P
><DIV
CLASS="EXAMPLE"
><A
NAME="RANDSTRING"
></A
><P
><B
>Example 10-2. Generating an 8-character <SPAN
CLASS="QUOTE"
>"random"</SPAN
>
string</B
></P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><FONT
COLOR="#000000"
><PRE
CLASS="PROGRAMLISTING"
>#!/bin/bash
# rand-string.sh
# Generating an 8-character "random" string.
if [ -n "$1" ] # If command-line argument present,
then #+ then set start-string to it.
str0="$1"
else # Else use PID of script as start-string.
str0="$$"
fi
POS=2 # Starting from position 2 in the string.
LEN=8 # Extract eight characters.
str1=$( echo "$str0" | md5sum | md5sum )
# Doubly scramble ^^^^^^ ^^^^^^
#+ by piping and repiping to md5sum.
randstring="${str1:$POS:$LEN}"
# Can parameterize ^^^^ ^^^^
echo "$randstring"
exit $?
# bozo$ ./rand-string.sh my-password
# 1bdd88c4
# No, this is is not recommended
#+ as a method of generating hack-proof passwords.</PRE
></FONT
></TD
></TR
></TABLE
></DIV
><P
><A
NAME="SUBSTREXTRP"
></A
></P
><P
>If the <TT
CLASS="VARNAME"
>$string</TT
> parameter is
<SPAN
CLASS="QUOTE"
>"<SPAN
CLASS="TOKEN"
>*</SPAN
>"</SPAN
> or
<SPAN
CLASS="QUOTE"
>"<SPAN
CLASS="TOKEN"
>@</SPAN
>"</SPAN
>, then this extracts a maximum
of <TT
CLASS="VARNAME"
>$length</TT
> positional parameters, starting
at <TT
CLASS="VARNAME"
>$position</TT
>.</P
><P
> <TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><FONT
COLOR="#000000"
><PRE
CLASS="PROGRAMLISTING"
>echo ${*:2} # Echoes second and following positional parameters.
echo ${@:2} # Same as above.
echo ${*:2:3} # Echoes three positional parameters, starting at second.</PRE
></FONT
></TD
></TR
></TABLE
>
</P
></DD
><DT
>expr substr $string $position $length</DT
><DD
><P
>Extracts <TT
CLASS="REPLACEABLE"
><I
>$length</I
></TT
> characters
from <TT
CLASS="REPLACEABLE"
><I
>$string</I
></TT
> starting at
<TT
CLASS="REPLACEABLE"
><I
>$position</I
></TT
>.</P
><P
> <TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><FONT
COLOR="#000000"
><PRE
CLASS="PROGRAMLISTING"
>stringZ=abcABC123ABCabc
# 123456789......
# 1-based indexing.
echo `expr substr $stringZ 1 2` # ab
echo `expr substr $stringZ 4 3` # ABC</PRE
></FONT
></TD
></TR
></TABLE
>
</P
><P
><A
NAME="EXPRPAREN"
></A
></P
></DD
><DT
>expr match "$string" '\($substring\)'</DT
><DD
><P
>Extracts <TT
CLASS="REPLACEABLE"
><I
>$substring</I
></TT
>
at beginning of <TT
CLASS="REPLACEABLE"
><I
>$string</I
></TT
>,
where <TT
CLASS="REPLACEABLE"
><I
>$substring</I
></TT
> is a <A
HREF="regexp.html#REGEXREF"
>regular expression</A
>.</P
></DD
><DT
>expr "$string" : '\($substring\)'</DT
><DD
><P
>Extracts <TT
CLASS="REPLACEABLE"
><I
>$substring</I
></TT
>
at beginning of <TT
CLASS="REPLACEABLE"
><I
>$string</I
></TT
>,
where <TT
CLASS="REPLACEABLE"
><I
>$substring</I
></TT
> is a regular
expression.</P
><P
> <TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><FONT
COLOR="#000000"
><PRE
CLASS="PROGRAMLISTING"
>stringZ=abcABC123ABCabc
# =======
echo `expr match "$stringZ" '\(.[b-c]*[A-Z]..[0-9]\)'` # abcABC1
echo `expr "$stringZ" : '\(.[b-c]*[A-Z]..[0-9]\)'` # abcABC1
echo `expr "$stringZ" : '\(.......\)'` # abcABC1
# All of the above forms give an identical result.</PRE
></FONT
></TD
></TR
></TABLE
>
</P
></DD
><DT
>expr match "$string" '.*\($substring\)'</DT
><DD
><P
>Extracts <TT
CLASS="REPLACEABLE"
><I
>$substring</I
></TT
>
at <EM
>end</EM
> of
<TT
CLASS="REPLACEABLE"
><I
>$string</I
></TT
>, where
<TT
CLASS="REPLACEABLE"
><I
>$substring</I
></TT
> is a regular
expression.</P
></DD
><DT
>expr "$string" : '.*\($substring\)'</DT
><DD
><P
>Extracts <TT
CLASS="REPLACEABLE"
><I
>$substring</I
></TT
>
at <EM
>end</EM
> of <TT
CLASS="REPLACEABLE"
><I
>$string</I
></TT
>,
where <TT
CLASS="REPLACEABLE"
><I
>$substring</I
></TT
> is a regular
expression.</P
><P
> <TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><FONT
COLOR="#000000"
><PRE
CLASS="PROGRAMLISTING"
>stringZ=abcABC123ABCabc
# ======
echo `expr match "$stringZ" '.*\([A-C][A-C][A-C][a-c]*\)'` # ABCabc
echo `expr "$stringZ" : '.*\(......\)'` # ABCabc</PRE
></FONT
></TD
></TR
></TABLE
>
</P
></DD
></DL
></DIV
><P
></P
><DIV
CLASS="VARIABLELIST"
><P
><B
>Substring Removal</B
></P
><DL
><DT
>${string#substring}</DT
><DD
><P
>Deletes shortest match of
<TT
CLASS="REPLACEABLE"
><I
>$substring</I
></TT
> from
<EM
>front</EM
> of
<TT
CLASS="REPLACEABLE"
><I
>$string</I
></TT
>.</P
></DD
><DT
>${string##substring}</DT
><DD
><P
>Deletes longest match of
<TT
CLASS="REPLACEABLE"
><I
>$substring</I
></TT
> from
<EM
>front</EM
> of
<TT
CLASS="REPLACEABLE"
><I
>$string</I
></TT
>.</P
><P
>
<TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><FONT
COLOR="#000000"
><PRE
CLASS="PROGRAMLISTING"
>stringZ=abcABC123ABCabc
# |----| shortest
# |----------| longest
echo ${stringZ#a*C} # 123ABCabc
# Strip out shortest match between 'a' and 'C'.
echo ${stringZ##a*C} # abc
# Strip out longest match between 'a' and 'C'.
# You can parameterize the substrings.
X='a*C'
echo ${stringZ#$X} # 123ABCabc
echo ${stringZ##$X} # abc
# As above.</PRE
></FONT
></TD
></TR
></TABLE
>
</P
></DD
><DT
>${string%substring}</DT
><DD
><P
>Deletes shortest match of
<TT
CLASS="REPLACEABLE"
><I
>$substring</I
></TT
> from
<EM
>back</EM
> of
<TT
CLASS="REPLACEABLE"
><I
>$string</I
></TT
>.</P
><P
>For example:
<TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><FONT
COLOR="#000000"
><PRE
CLASS="PROGRAMLISTING"
># Rename all filenames in $PWD with "TXT" suffix to a "txt" suffix.
# For example, "file1.TXT" becomes "file1.txt" . . .
SUFF=TXT
suff=txt
for i in $(ls *.$SUFF)
do
mv -f $i ${i%.$SUFF}.$suff
# Leave unchanged everything *except* the shortest pattern match
#+ starting from the right-hand-side of the variable $i . . .
done ### This could be condensed into a "one-liner" if desired.
# Thank you, Rory Winston.</PRE
></FONT
></TD
></TR
></TABLE
>
</P
></DD
><DT
>${string%%substring}</DT
><DD
><P
>Deletes longest match of
<TT
CLASS="REPLACEABLE"
><I
>$substring</I
></TT
> from
<EM
>back</EM
> of
<TT
CLASS="REPLACEABLE"
><I
>$string</I
></TT
>.</P
><P
>
<TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><FONT
COLOR="#000000"
><PRE
CLASS="PROGRAMLISTING"
>stringZ=abcABC123ABCabc
# || shortest
# |------------| longest
echo ${stringZ%b*c} # abcABC123ABCa
# Strip out shortest match between 'b' and 'c', from back of $stringZ.
echo ${stringZ%%b*c} # a
# Strip out longest match between 'b' and 'c', from back of $stringZ.</PRE
></FONT
></TD
></TR
></TABLE
>
</P
><P
>This operator is useful for generating filenames.</P
><DIV
CLASS="EXAMPLE"
><A
NAME="CVT"
></A
><P
><B
>Example 10-3. Converting graphic file formats, with filename change</B
></P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><FONT
COLOR="#000000"
><PRE
CLASS="PROGRAMLISTING"
>#!/bin/bash
# cvt.sh:
# Converts all the MacPaint image files in a directory to "pbm" format.
# Uses the "macptopbm" binary from the "netpbm" package,
#+ which is maintained by Brian Henderson (bryanh@giraffe-data.com).
# Netpbm is a standard part of most Linux distros.
OPERATION=macptopbm
SUFFIX=pbm # New filename suffix.
if [ -n "$1" ]
then
directory=$1 # If directory name given as a script argument...
else
directory=$PWD # Otherwise use current working directory.
fi
# Assumes all files in the target directory are MacPaint image files,
#+ with a ".mac" filename suffix.
for file in $directory/* # Filename globbing.
do
filename=${file%.*c} # Strip ".mac" suffix off filename
#+ ('.*c' matches everything
#+ between '.' and 'c', inclusive).
$OPERATION $file &#62; "$filename.$SUFFIX"
# Redirect conversion to new filename.
rm -f $file # Delete original files after converting.
echo "$filename.$SUFFIX" # Log what is happening to stdout.
done
exit 0
# Exercise:
# --------
# As it stands, this script converts *all* the files in the current
#+ working directory.
# Modify it to work *only* on files with a ".mac" suffix.
# *** And here's another way to do it. *** #
#!/bin/bash
# Batch convert into different graphic formats.
# Assumes imagemagick installed (standard in most Linux distros).
INFMT=png # Can be tif, jpg, gif, etc.
OUTFMT=pdf # Can be tif, jpg, gif, pdf, etc.
for pic in *"$INFMT"
do
p2=$(ls "$pic" | sed -e s/\.$INFMT//)
# echo $p2
convert "$pic" $p2.$OUTFMT
done
exit $?</PRE
></FONT
></TD
></TR
></TABLE
></DIV
><DIV
CLASS="EXAMPLE"
><A
NAME="RA2OGG"
></A
><P
><B
>Example 10-4. Converting streaming audio files to
<I
CLASS="FIRSTTERM"
>ogg</I
></B
></P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><FONT
COLOR="#000000"
><PRE
CLASS="PROGRAMLISTING"
>#!/bin/bash
# ra2ogg.sh: Convert streaming audio files (*.ra) to ogg.
# Uses the "mplayer" media player program:
# http://www.mplayerhq.hu/homepage
# Uses the "ogg" library and "oggenc":
# http://www.xiph.org/
#
# This script may need appropriate codecs installed, such as sipr.so ...
# Possibly also the compat-libstdc++ package.
OFILEPREF=${1%%ra} # Strip off the "ra" suffix.
OFILESUFF=wav # Suffix for wav file.
OUTFILE="$OFILEPREF""$OFILESUFF"
E_NOARGS=85
if [ -z "$1" ] # Must specify a filename to convert.
then
echo "Usage: `basename $0` [filename]"
exit $E_NOARGS
fi
##########################################################################
mplayer "$1" -ao pcm:file=$OUTFILE
oggenc "$OUTFILE" # Correct file extension automatically added by oggenc.
##########################################################################
rm "$OUTFILE" # Delete intermediate *.wav file.
# If you want to keep it, comment out above line.
exit $?
# Note:
# ----
# On a Website, simply clicking on a *.ram streaming audio file
#+ usually only downloads the URL of the actual *.ra audio file.
# You can then use "wget" or something similar
#+ to download the *.ra file itself.
# Exercises:
# ---------
# As is, this script converts only *.ra filenames.
# Add flexibility by permitting use of *.ram and other filenames.
#
# If you're really ambitious, expand the script
#+ to do automatic downloads and conversions of streaming audio files.
# Given a URL, batch download streaming audio files (using "wget")
#+ and convert them on the fly.</PRE
></FONT
></TD
></TR
></TABLE
></DIV
><P
><A
NAME="GETOPTSIMPLE1"
></A
></P
><P
>A simple emulation of <A
HREF="extmisc.html#GETOPTY"
>getopt</A
>
using substring-extraction constructs.</P
><DIV
CLASS="EXAMPLE"
><A
NAME="GETOPTSIMPLE"
></A
><P
><B
>Example 10-5. Emulating <I
CLASS="FIRSTTERM"
>getopt</I
></B
></P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><FONT
COLOR="#000000"
><PRE
CLASS="PROGRAMLISTING"
>#!/bin/bash
# getopt-simple.sh
# Author: Chris Morgan
# Used in the ABS Guide with permission.
getopt_simple()
{
echo "getopt_simple()"
echo "Parameters are '$*'"
until [ -z "$1" ]
do
echo "Processing parameter of: '$1'"
if [ ${1:0:1} = '/' ]
then
tmp=${1:1} # Strip off leading '/' . . .
parameter=${tmp%%=*} # Extract name.
value=${tmp##*=} # Extract value.
echo "Parameter: '$parameter', value: '$value'"
eval $parameter=$value
fi
shift
done
}
# Pass all options to getopt_simple().
getopt_simple $*
echo "test is '$test'"
echo "test2 is '$test2'"
exit 0 # See also, UseGetOpt.sh, a modified version of this script.
---
sh getopt_example.sh /test=value1 /test2=value2
Parameters are '/test=value1 /test2=value2'
Processing parameter of: '/test=value1'
Parameter: 'test', value: 'value1'
Processing parameter of: '/test2=value2'
Parameter: 'test2', value: 'value2'
test is 'value1'
test2 is 'value2'&#13;</PRE
></FONT
></TD
></TR
></TABLE
></DIV
></DD
></DL
></DIV
><P
></P
><DIV
CLASS="VARIABLELIST"
><P
><B
>Substring Replacement</B
></P
><DL
><DT
><A
NAME="SUBSTRREPL00"
></A
>${string/substring/replacement}</DT
><DD
><P
> Replace first <I
CLASS="FIRSTTERM"
>match</I
> of
<TT
CLASS="REPLACEABLE"
><I
>$substring</I
></TT
> with
<TT
CLASS="REPLACEABLE"
><I
>$replacement</I
></TT
>.
<A
NAME="AEN6164"
HREF="#FTN.AEN6164"
><SPAN
CLASS="footnote"
>[2]</SPAN
></A
>
</P
></DD
><DT
><A
NAME="SUBSTRREPL01"
></A
>${string//substring/replacement}</DT
><DD
><P
>Replace all matches of
<TT
CLASS="REPLACEABLE"
><I
>$substring</I
></TT
> with
<TT
CLASS="REPLACEABLE"
><I
>$replacement</I
></TT
>.</P
><P
>
<TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><FONT
COLOR="#000000"
><PRE
CLASS="PROGRAMLISTING"
>stringZ=abcABC123ABCabc
echo ${stringZ/abc/xyz} # xyzABC123ABCabc
# Replaces first match of 'abc' with 'xyz'.
echo ${stringZ//abc/xyz} # xyzABC123ABCxyz
# Replaces all matches of 'abc' with # 'xyz'.
echo ---------------
echo "$stringZ" # abcABC123ABCabc
echo ---------------
# The string itself is not altered!
# Can the match and replacement strings be parameterized?
match=abc
repl=000
echo ${stringZ/$match/$repl} # 000ABC123ABCabc
# ^ ^ ^^^
echo ${stringZ//$match/$repl} # 000ABC123ABC000
# Yes! ^ ^ ^^^ ^^^
echo
# What happens if no $replacement string is supplied?
echo ${stringZ/abc} # ABC123ABCabc
echo ${stringZ//abc} # ABC123ABC
# A simple deletion takes place.</PRE
></FONT
></TD
></TR
></TABLE
>
</P
></DD
><DT
><A
NAME="SUBSTRREPL02"
></A
>${string/#substring/replacement}</DT
><DD
><P
>If <TT
CLASS="REPLACEABLE"
><I
>$substring</I
></TT
> matches
<EM
>front</EM
> end of
<TT
CLASS="REPLACEABLE"
><I
>$string</I
></TT
>, substitute
<TT
CLASS="REPLACEABLE"
><I
>$replacement</I
></TT
> for
<TT
CLASS="REPLACEABLE"
><I
>$substring</I
></TT
>.</P
></DD
><DT
><A
NAME="SUBSTRREPL03"
></A
>${string/%substring/replacement}</DT
><DD
><P
>If <TT
CLASS="REPLACEABLE"
><I
>$substring</I
></TT
> matches
<EM
>back</EM
> end of
<TT
CLASS="REPLACEABLE"
><I
>$string</I
></TT
>, substitute
<TT
CLASS="REPLACEABLE"
><I
>$replacement</I
></TT
> for
<TT
CLASS="REPLACEABLE"
><I
>$substring</I
></TT
>.</P
><P
>
<TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><FONT
COLOR="#000000"
><PRE
CLASS="PROGRAMLISTING"
>stringZ=abcABC123ABCabc
echo ${stringZ/#abc/XYZ} # XYZABC123ABCabc
# Replaces front-end match of 'abc' with 'XYZ'.
echo ${stringZ/%abc/XYZ} # abcABC123ABCXYZ
# Replaces back-end match of 'abc' with 'XYZ'.</PRE
></FONT
></TD
></TR
></TABLE
>
</P
></DD
></DL
></DIV
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="AWKSTRINGMANIP"
></A
>10.1.1. Manipulating strings using awk</H2
><P
><A
NAME="AWKSTRINGMANIP2"
></A
></P
><P
>A Bash script may invoke the string manipulation facilities of
<A
HREF="awk.html#AWKREF"
>awk</A
> as an alternative to using its
built-in operations.</P
><DIV
CLASS="EXAMPLE"
><A
NAME="SUBSTRINGEX"
></A
><P
><B
>Example 10-6. Alternate ways of extracting and locating substrings</B
></P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><FONT
COLOR="#000000"
><PRE
CLASS="PROGRAMLISTING"
>#!/bin/bash
# substring-extraction.sh
String=23skidoo1
# 012345678 Bash
# 123456789 awk
# Note different string indexing system:
# Bash numbers first character of string as 0.
# Awk numbers first character of string as 1.
echo ${String:2:4} # position 3 (0-1-2), 4 characters long
# skid
# The awk equivalent of ${string:pos:length} is substr(string,pos,length).
echo | awk '
{ print substr("'"${String}"'",3,4) # skid
}
'
# Piping an empty "echo" to awk gives it dummy input,
#+ and thus makes it unnecessary to supply a filename.
echo "----"
# And likewise:
echo | awk '
{ print index("'"${String}"'", "skid") # 3
} # (skid starts at position 3)
' # The awk equivalent of "expr index" ...
exit 0</PRE
></FONT
></TD
></TR
></TABLE
></DIV
></DIV
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="STRFDISC"
></A
>10.1.2. Further Reference</H2
><P
>For more on string manipulation in scripts, refer to <A
HREF="parameter-substitution.html"
>Section 10.2</A
> and the
<A
HREF="moreadv.html#EXPEXTRSUB"
>relevant section</A
> of the <A
HREF="moreadv.html#EXPRREF"
>expr</A
> command listing.</P
><P
>Script examples:
<P
></P
><OL
TYPE="1"
><LI
><P
><A
HREF="moreadv.html#EX45"
>Example 16-9</A
></P
></LI
><LI
><P
><A
HREF="parameter-substitution.html#LENGTH"
>Example 10-9</A
></P
></LI
><LI
><P
><A
HREF="parameter-substitution.html#PATTMATCHING"
>Example 10-10</A
></P
></LI
><LI
><P
><A
HREF="parameter-substitution.html#RFE"
>Example 10-11</A
></P
></LI
><LI
><P
><A
HREF="parameter-substitution.html#VARMATCH"
>Example 10-13</A
></P
></LI
><LI
><P
><A
HREF="contributed-scripts.html#INSERTIONSORT"
>Example A-36</A
></P
></LI
><LI
><P
><A
HREF="contributed-scripts.html#QKY"
>Example A-41</A
></P
></LI
></OL
>
</P
></DIV
></DIV
><H3
CLASS="FOOTNOTES"
>Notes</H3
><TABLE
BORDER="0"
CLASS="FOOTNOTES"
WIDTH="100%"
><TR
><TD
ALIGN="LEFT"
VALIGN="TOP"
WIDTH="5%"
><A
NAME="FTN.AEN5987"
HREF="string-manipulation.html#AEN5987"
><SPAN
CLASS="footnote"
>[1]</SPAN
></A
></TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
WIDTH="95%"
><P
>This applies to either command-line
arguments or parameters passed to a <A
HREF="functions.html#FUNCTIONREF"
>function</A
>.</P
></TD
></TR
><TR
><TD
ALIGN="LEFT"
VALIGN="TOP"
WIDTH="5%"
><A
NAME="FTN.AEN6164"
HREF="string-manipulation.html#AEN6164"
><SPAN
CLASS="footnote"
>[2]</SPAN
></A
></TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
WIDTH="95%"
><P
>Note that
<TT
CLASS="REPLACEABLE"
><I
>$substring</I
></TT
> and
<TT
CLASS="REPLACEABLE"
><I
>$replacement</I
></TT
> may refer to
either <I
CLASS="FIRSTTERM"
>literal strings</I
> or
<I
CLASS="FIRSTTERM"
>variables</I
>, depending on
context. See the first usage example.</P
></TD
></TR
></TABLE
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