Programmeren in de Shell

ArticleCategory:

AuthorImage:

TranslationInfo:

original in en Katja en Guido Socher 

en to nl Floris Lambrechts

AboutTheAuthor:

Katja is de Duitse hoofdredactrice van LinuxFocus. Ze houdt van Tux, film & fotografie en de zee. Haar homepage vind je hier.

Guido is al lang een Linux-fan omdat het gemaakt wordt door eerlijke en open mensen. Dat is één van de redenen waarom we het open source noemen. Zijn homepage staat op linuxfocus.org/~guido.

Abstract:

ArticleIllustration:

ArticleBody:

Waarom programmeren in de shell?

Een script maken

    #!/bin/sh 

    chmod +x bestandsnaam

Commentaar

Variabelen

    varnaam=waarde

    #!/bin/sh
    # assign a value:
    a="hello world"
    # now print the content of "a":
    echo "A is:"
    echo $a

    A is:
    hello world

    num=2
    echo "dit is de $numde"

    num=2
    echo "dit is de ${num}de"

Shell-commando's en controlestructuren

 cat bestand.txt | awk -F, '{print $1 "," $3 }' 

Adam Bor, 34, India
Kerry Miller, 22, USA

Adam Bor, India
Kerry Miller, USA

    grep "hello" bestand.txt | wc -l

find . -mtime -1 -type f -print

tar xvf archief.tar bestand1 bestand2 ...

#!/bin/sh
# De aanhalingstekens zijn backticks (`), geen gewone (') ! 
tar -zcvf gewijzigd.tar.gz `find . -mtime -1 -type f -print`

if ....; then
   ....
elif ....; then
   ....
else
   ....
fi

[ -f "eenbestand" ]  : Test of eenbestand wel echt een bestand is.
[ -x "/bin/ls" ]   : Test of /bin/ls bestaat en of het uitvoerbaar is.
[ -n "$var" ]      : Test of de variabele $var wel een waarde heeft.
[ "$a" = "$b" ]    : Test of de variabelen "$a" en "$b" hetzelfde zijn.

#!/bin/sh
if [ "$SHELL" = "/bin/bash" ]; then
  echo "your login shell is the bash (bourne again shell)"
else
  echo "your login shell is not bash but $SHELL"
fi

[ -f "/etc/shadow" ] && echo "This computer uses shadow passwords"

#!/bin/sh
mailfolder=/var/spool/mail/james
[ -r "$mailfolder" ] || { echo "Can not read $mailfolder" ; exit 1; }
echo "$mailfolder has mail from:"
grep "^From " $mailfolder

case ... in
...) doe hier iets;;
esac

file lf.gz

lf.gz: gzip compressed data, deflated, original filename,
last modified: Mon Aug 27 23:09:18 2001, os: Unix

#!/bin/sh
ftype=`file "$1"`
case "$ftype" in
"$1: Zip archive"*)
    unzip "$1" ;;
"$1: gzip compressed"*)
    gunzip "$1" ;;
"$1: bzip2 compressed"*)
    bunzip2 "$1" ;;
*) error "File $1 can not be uncompressed with smartzip";;
esac

select var in ... ; do
  break
done
.... nu kun je $var gebruiken ....

#!/bin/sh
echo "What is your favourite OS?"
select var in "Linux" "Gnu Hurd" "Free BSD" "Other"; do
        break
done
echo "You have selected $var"

What is your favourite OS?
1) Linux
2) Gnu Hurd
3) Free BSD
4) Other
#? 1
You have selected Linux

while ...; do
 ....
done

for var in ....; do
  ....
done

#!/bin/sh
for var in A B C ; do
  echo "var is $var"
done

#!/bin/sh
# list a content summary of a number of RPM packages
# USAGE: showrpm rpmfile1 rpmfile2 ...
# EXAMPLE: showrpm /cdrom/RedHat/RPMS/*.rpm
for rpmpackage in $*; do
  if [ -r "$rpmpackage" ];then
    echo "=============== $rpmpackage =============="
    rpm -qi -p $rpmpackage
  else
    echo "ERROR: cannot read file $rpmpackage"
  fi
done

#!/bin/sh
echo *.jpg

#!/bin/sh
echo "*.jpg"
echo '*.jpg'

#!/bin/sh
echo $SHELL
echo "$SHELL"
echo '$SHELL'

/bin/bash
/bin/bash
$SHELL

echo \*.jpg
echo \$SHELL

*.jpg
$SHELL

#!/bin/sh
# we have less than 3 arguments. Print the help text:
if [ $# -lt 3 ] ; then
cat <<HELP
ren -- renames a number of files using sed regular expressions

USAGE: ren 'regexp' 'replacement' files...

EXAMPLE: rename all *.HTM files in *.html:
  ren 'HTM$' 'html' *.HTM

HELP
  exit 0
fi
OLD="$1"
NEW="$2"
# The shift command removes one argument from the list of
# command line arguments.
shift
shift
# $* contains now all the files:
for file in $*; do
    if [ -f "$file" ] ; then
      newfile=`echo "$file" | sed "s/${OLD}/${NEW}/g"`
      if [ -f "$newfile" ]; then
        echo "ERROR: $newfile exists already"
      else
        echo "renaming $file to $newfile ..."
        mv "$file" "$newfile"
      fi
    fi
done

functienaam()
{
 # binnnen de functie is $1 het eerste argument gegeven aan de functie
 # $2 het tweede ...
 code
}

#!/bin/sh
# vim: set sw=4 ts=4 et:

help()
{
    cat <<HELP
xtitlebar -- change the name of an xterm, gnome-terminal or kde konsole

USAGE: xtitlebar [-h] "string_for_titelbar"

OPTIONS: -h help text

EXAMPLE: xtitlebar "cvs"

HELP
    exit 0
}

# in case of error or if -h is given we call the function help:
[ -z "$1" ] && help
[ "$1" = "-h" ] && help

# send the escape sequence to change the xterm titelbar:
echo -e "\033]0;$1\007"
#

#!/bin/sh
help()
{
  cat <<HELP
This is a generic command line parser demo.
USAGE EXAMPLE: cmdparser -l hello -f -- -somefile1 somefile2
HELP
  exit 0
}

while [ -n "$1" ]; do
case $1 in
    -h) help;shift 1;; # function help is called
    -f) opt_f=1;shift 1;; # variable opt_f is set
    -l) opt_l=$2;shift 2;; # -l takes an argument -> shift by 2
    --) shift;break;; # end of options
    -*) echo "error: no such option $1. -h for help";exit 1;;
    *)  break;;
esac
done

echo "opt_f is $opt_f"
echo "opt_l is $opt_l"
echo "first arg is $1"
echo "2nd arg is $2"

cmdparser -l hello -f -- -eenbestand1 eenbestand2

opt_f is 1
opt_l is hello
first arg is -eenbestand1
2nd arg is eenbestand2

Zoek naar -xx- in bestand f.txt:
grep -- -xx- f.txt

Voorbeelden

cp framework.sh mijnscript

#!/bin/sh
# vim: set sw=4 ts=4 et:
help()
{
  cat <<HELP
b2h -- convert binary to decimal

USAGE: b2h [-h] binarynum

OPTIONS: -h help text

EXAMPLE: b2h 111010
will return 58
HELP
  exit 0
}

error()
{
    # print an error and exit
    echo "$1"
    exit 1
}

lastchar()
{
    # return the last character of a string in $rval
    if [ -z "$1" ]; then
        # empty string
        rval=""
        return
    fi
    # wc puts some space behind the output this is why we need sed:
    numofchar=`echo -n "$1" | wc -c | sed 's/ //g' `
    # now cut out the last char
    rval=`echo -n "$1" | cut -b $numofchar`
}

chop()
{
    # remove the last character in string and return it in $rval
    if [ -z "$1" ]; then
        # empty string
        rval=""
        return
    fi
    # wc puts some space behind the output this is why we need sed:
    numofchar=`echo -n "$1" | wc -c | sed 's/ //g' `
    if [ "$numofchar" = "1" ]; then
        # only one char in string
        rval=""
        return
    fi
    numofcharminus1=`expr $numofchar "-" 1` 
    # now cut all but the last char:
    rval=`echo -n "$1" | cut -b 0-${numofcharminus1}`
}
    

while [ -n "$1" ]; do
case $1 in
    -h) help;shift 1;; # function help is called
    --) shift;break;; # end of options
    -*) error "error: no such option $1. -h for help";;
    *)  break;;
esac
done

# The main program
sum=0
weight=1
# one arg must be given:
[ -z "$1" ] && help
binnum="$1"
binnumorig="$1"

while [ -n "$binnum" ]; do
    lastchar "$binnum"
    if [ "$rval" = "1" ]; then
        sum=`expr "$weight" "+" "$sum"`
    fi
    # remove the last position in $binnum
    chop "$binnum"
    binnum="$rval"
    weight=`expr "$weight" "*" 2`
done

echo "binary $binnumorig is decimal $sum"
#

#!/bin/sh
# vim: set sw=4 ts=4 et: 
ver="0.1"
help()
{
    cat <<HELP
rotatefile -- rotate the file name 

USAGE: rotatefile [-h]  filename

OPTIONS: -h help text

EXAMPLE: rotatefile out
This will e.g rename out.2 to out.3, out.1 to out.2, out to out.1
and create an empty out-file

The max number is 10

version $ver
HELP
    exit 0
}

error()
{
    echo "$1"
    exit 1
}
while [ -n "$1" ]; do
case $1 in
    -h) help;shift 1;;
    --) break;;
    -*) echo "error: no such option $1. -h for help";exit 1;;
    *)  break;;
esac
done

# input check:
if [ -z "$1" ] ; then
 error "ERROR: you must specify a file, use -h for help" 
fi
filen="$1"
# rename any .1 , .2 etc file:
for n in  9 8 7 6 5 4 3 2 1; do
    if [ -f "$filen.$n" ]; then
        p=`expr $n + 1`
        echo "mv $filen.$n $filen.$p"
        mv $filen.$n $filen.$p
    fi
done
# rename the original file:
if [ -f "$filen" ]; then
    echo "mv $filen $filen.1"
    mv $filen $filen.1
fi
echo touch $filen
touch $filen

Debuggen

sh -x foutscript

sh -n je_script

Referenties

• De man- en info-pagina's van bash zijn zeer goed en je kunt er nog veel trucs in ontdekken:
  man bash
  tkinfo bash
  (Ik haat de standaard info-browser maar tkinfo of konqueror (de url is info:/bash/Top ) zijn vrij goed)
• Het LinuxFocus artikel over GNU-hulpmiddelen voor bestanden
• Het LinuxFocus artikel over Reguliere expressies
• Het LinuxFocus artikel over AWK
• Het LinuxFocus artikel over Fundamentele UNIX-commando's
• Als bash niet op je systeem staat of als je de nieuwste versie wilt dan kan je die downloaden van de GNU-website op http://www.gnu.org. (Wil je weten of je bash hebt of niet typ dan "bash". Als er geen foutmelding verschijnt dan is het geïnstalleerd.)