Variables and arguments

Assign with variable=value and get content with $variable

MESSAGE="Hello World" # Assign a string

PI=3.1415 # Assign a decimal number

N=8

TWON=`expr $N * 2` # Arithmetic expression (only integers)

TWON=$(($N * 2)) # Other syntax

TWOPI=`echo "$PI * 2" | bc -l` # Use bc for floating point operations

ZERO=`echo "c($PI/4)-sqrt(2)/2" | bc -l`

The command line arguments are

$0, $1, $2, ... # $0 is the command itself

$# # The number of arguments

$* # All arguments (also $@)

Special Variables

$$ # The current process ID

$? # exit status of last command

command

if [ $? != 0 ]; then

echo "command failed"

fi

mypath=`pwd`

mypath=${mypath}/file.txt

echo ${mypath##*/} # Display the filename only

echo ${mypath%%.*} # Full path without extention

var2=${var:=string} # Use var if set, otherwise use string

# assign string to var and then to var2.

Constructs

for file in `ls`

do

echo $file

done

count=0

while [ $count -lt 5 ]; do

echo $count

sleep 1

count=$(($count + 1))

done

myfunction() {

find . -type f -name "*.$1" -print # $1 is first argument of the function

}

myfunction "txt"

Generate a file

MYHOME=/home/colin

cat > testhome.sh << _EOF

# All of this goes into the file testhome.sh

if [ -d "$MYHOME" ] ; then

echo $MYHOME exists

else

echo $MYHOME does not exist

fi

_EOF

sh testhome.sh

As a small example, the script used to create a PDF booklet from this xhtml document:

#!/bin/sh

# This script creates a book in pdf format ready to print on a duplex printer

if [ $# -ne 1 ]; then # Check the argument

echo 1>&2 "Usage: $0 HtmlFile"

exit 1 # non zero exit if error

fi

file=$1 # Assign the filename

fname=${file%.*} # Get the name of the file only

fext=${file#*.} # Get the extension of the file

prince $file -o $fname.pdf # from www.princexml.com

pdftops -paper A4 -noshrink $fname.pdf $fname.ps # create postscript booklet

cat $fname.ps |psbook|psnup -Pa4 -2 |pstops -b "2:0,1U(21cm,29.7cm)" > $fname.book.ps

ps2pdf13 -sPAPERSIZE=a4 -sAutoRotatePages=None $fname.book.ps $fname.book.pdf

# use #a4 and #None on Windows!

exit 0 # exit 0 means successful

sed 's/string1/string2/g' # Replace string1 with string2

sed -i 's/wroong/wrong/g' *.txt # Replace a recurring word with g

sed 's/\(.*\)1/\12/g' # Modify anystring1 to anystring2

sed '/<p>/,/<\/p>/d' t.xhtml # Delete lines that start with <p>

# and end with </p>

sed '/ *#/d; /^ *$/d' # Remove comments and blank lines

sed 's/[ \t]*$//' # Remove trailing spaces (use tab as \t)

sed 's/^[ \t]*//;s/[ \t]*$//' # Remove leading and trailing spaces

sed 's/[^*]/[&]/' # Enclose first char with [] top->[t]op

sort -t. -k1,1n -k2,2n -k3,3n -k4,4n # Sort IPv4 ip addresses

echo 'Test' | tr '[:lower:]' '[:upper:]' # Case conversion

echo foo.bar | cut -d . -f 1 # Returns foo

PID=$(ps | grep script.sh | grep bin | awk '{print $1}') # PID of a running script

PID=$(ps axww | grep [p]ing | awk '{print $1}') # PID of ping (w/o grep pid)

IP=$(ifconfig $INTERFACE | sed '/.*inet addr:/!d;s///;s/ .*//') # Linux

IP=$(ifconfig $INTERFACE | sed '/.*inet /!d;s///;s/ .*//') # FreeBSD

if [ `diff file1 file2 | wc -l` != 0 ]; then [...] fi # File changed?

cat /etc/master.passwd | grep -v root | grep -v \*: | awk -F":" \ # Create http passwd

'{ printf("%s:%s\n", $1, $2) }' > /usr/local/etc/apache2/passwd

testuser=$(cat /usr/local/etc/apache2/passwd | grep -v \ # Check user in passwd

root | grep -v \*: | awk -F":" '{ printf("%s\n", $1) }' | grep ^user$)