ShellAdvanced aaäaaaaaaaaaaaaaaaaaaaaaaaaaaa

CISC3130, Spring 2013
Dr. Zhang
1
Bash Scripting: Advanced Topics

Outline
2
 Review HW1, HW2 and Quiz2
 Review of standard input/output/error
 How to redirect them ?
 Pipeline
 Review of bash scripting
 Functions
 Here documents
 Arrays

Homework 2
 match phone numbers in text file
 7188174484, 718-817-4484, (718)817,4484
 817-4484, or 817,4484, 8174484.
 (01)718,817,4484, 01,718-817-4484
 grep -f phone.grep file.txt , where phone.grep:
[^0-9][0-9]{10}$
[^0-9][0-9]{10}[^0-9]
[^0-9][0-9]{3}-[0-9]{3}-[0-9]{4}$
[^0-9][0-9]{3}-[0-9]{3}-[0-9]{4}[^0-9]
[^0-9][0-9]{3},[0-9]{4}$
[^0-9][0-9]{3},[0-9]{4}[^0-9]
[^0-9][0-9]{3}-[0-9]{4}$
[^0-9][0-9]{3}-[0-9]{4}[^0-9]
3
Match 10 digits at end of line
Match 10 digits, and a non-digit char
718-817,4484 at end of line

Homework 2
[^0-9]*([0-9]{2})([0-9]{3})[0-9]{3},[0-9]{4}$
[^0-9]*([0-9]{2})([0-9]{3})[0-9]{3},[0-9]{4}[^0-9]
[^0-9]*([0-9]{2})([0-9]{3}))?[0-9]{3}-[0-9]{4}$
[^0-9]*([0-9]{2})([0-9]{3}))?[0-9]{3}-[0-9]{4}[^0-9]
[^0-9]*[0-9]{2},[0-9]{3},[0-9]{3},[0-9]{4}$
[^0-9]*[0-9]{2},[0-9]{3}-[0-9]{3}-[0-9]{4}[^0-9]
[^0-9]*[0-9]{2},[0-9]{3}-[0-9]{3}-[0-9]{4}$
[^0-9]*[0-9]{2},[0-9]{3},[0-9]{3},[0-9]{4}[^0-9]
4

Homework 2
 Write a sed script file that remove all one-line
comments from C/C++ source code files. Note that
such comments starting with //, and ends at the end of
line. You need to take care the cases where //
appears in double quote, or single quote, in thsse
cases, what comes after // is not comment.
 rmcnt.sed :
#!/bin/sed -f
## remove one-line comments from C/C++ code
/^[^'"]*/// s///.*$/ /g
 rmcnt.sed sample.cpp
5
Apply to lines that contain // not preceding by ' or "
Replace // and following chars
with space

Quiz 2
 How to write to standard output in shell script:
#!/bin/bash
echo "Hello world";
echo "Something is wrong" 1>& 2
ls ABCDEF 2>&1
 Try it out:
 ./test_redirect.sh 2> err_out ## what happens?
 ./test_redirect.sh > std_out ## what happens?
 ./test_redirect.sh > std_out 2>&1
6

Quiz2
 Mark constants with < and >
#/bin/bash
# First find numerica constants in the code
#grep -E '[^a-zA-Z_][0-9]+.?[0-9]+' $1
# now mark constants with <>
echo mark constants in file $1
sed 's/([^a-zA-Z0-9_])([0-9][0-9]*.{0,1}[0-9][0-9]*)/1<2>/g' $1
7
The char before constant:
not alphabet, not _, and not
digit
A numeric constant:
Optional decimal points: .{0,1}
cannot use ?, as sed use BRE

Standard input/output/error
8
 By default, link to keyboard and terminal window
respectively
 Can be redirected to files
 Can be redirected to pipeline
 input can be redirected to reading end of a pipe
 output and error can be redirected to writing end of a pipe
 When a bash script’s input/output/error is
redirected:
 E.g., headtail 3 10 .bash_profile > output
 ls –l | headtail 10 24 | wc –l
 input/output/error for every command in the script are
redirected !

Save standard input if necessary
9
#!/bin/bash
# Count # of lines, and search for phone in a file; if a file is
# not specified, process standard input
set -x ## turn on execution tracing
if [ $# -eq 0 ]
then
cat > stdinput ## save standard input to a file
set stdinput
fi
## so that we can use as many times as we want
wc –l $*
grep -f phone.grep $*
rm stdinput
exit 0
Or use –x in
first line, i.e., #!/bin/bash –x
Or type
$ bash -x countlines_searchphoneno.sh
to run the scripts
Code at:
countlines_searchphoneno.sh

Redirection can be applied to
loop
10
rm all_shellscripts
for i in `ls *.sh`
do
echo $i
>>all_shellscripts
cat $i >>all_shellscripts
done
for i in `ls *.sh`
do
echo $i
cat $i
done >
all_shellscripts
Similar for <, |

case construct: branching
 case construct is analogus to switch in C/C++.
case "$variable" in
shellpattern1 )
command...
;;
shellpattern2)
command …
;;
shell pattern n)
command...
;;
esac
11
• Quoting variables is not
mandatory
• Each pattern can contain shell
wildcard (*,?,[a-z]), ends with a )
• Each condition block ends with ;;
• If a condition tests true, then
associated commands execute and
the case block terminates.
• entire case block ends with an
esac

Calculator using case block
case "$op" in
"+" ) result=$(($x + $y))
echo $x $op $y = $result;;
"-" ) result=$(($x - $y))
"*" ) result=$(($x * $y))
echo $x * $y = $result;;
"/" ) result=$(($x / $y))
* ) echo Unknow operator $op;;
esac
12

#!/bin/bash
OPT=$1 # option
FILE=$2 # filename
# test -e and -E command line args matching
case $OPT in
-e|-E)
echo "Editing $2 file..."
# make sure filename is passed else an error displayed
[ -z $FILE ] && { echo "File name missing"; exit 1; } || vi $FILE
;;
-c|-C)
echo "Displaying $2 file...“
[ -z $FILE ] && { echo "File name missing"; exit 1; } || cat
$FILE ;;
-d|-D)
echo "Today is $(date)" ;;
*)
echo "Bad argument!"
echo "Usage: $0 -ecd filename"
echo " -e file : Edit file."
echo " -c file : Display file."
13
test if string is null
Lazy evaluation of && and ||

Case example
case $1 in
-f)
## case for –f option
;;
-d | --directory)
## -f or –directory option
;;
*)
echo $1: unknown option >&2
exit 1;
esac
14

More about bash loop structures
15

Infinite loop
16
while [ 1 ]
do
echo -n "Enter your password"
read input
if [ $input = "secret" ]
then
break ## break out of the loop
else
echo -n "Try again... "
fi
done

continue command
 Continue from the top of the for loop
 Ignore rest of commands in the loop, and continue the loop
from the top again (for the next value in the list)
i=1
for day in Mon Tue Wed Thu Fri Sat Sun
do
echo -n "Day $((i++)) : $day"
if [ $i -eq 7 -o $i -eq 8 ];
then
echo " (WEEKEND)"
continue;
fi
echo " (weekday)"
done
17

For loop without a list
#!/bin/bash
for i
do
echo hello $i
done
18

For loop
i=1
for username in `awk -F: '{print $1}' /etc/passwd`
do
echo "Username $((i++)) : $username"
done
19

Loop through files/directories
 loop through files and directories under a specific
directory
i=1
cd ~
for item in *
do
echo "Item $((i++)) : $item"
done
20

C-Style for loop
for (( EXP1; EXP2; EXP3 ))
do
Command1
…
Commandn
done
 Example:
#!/bin/bash
for (( c=1; c<=5; c++ ))
do
echo "Welcome $c times“
done
21
EXP1: initializer
EXP2: a loop-test or condition
EXP3: counting expression

Select loop
 select construct: allows easy menu generation
select WORD [in LIST]
do
RESPECTIVE-COMMANDS;
done
1. List of items printed to standard error, each item preceded by a
number.
 If in LIST is not present, positional parameters (command line
arguments) are used
2. A prompt is printed, one line from standard input is read.
1.If input is a number corresponding to one of items, value of WORD is
set to name of that item.
2.If line is empty, items and the PS3 prompt are displayed again.
3. If an EOF (End Of File) is read, loop exits.
3. RESPECTIVE-COMMANDS are executed after each selection
22

select construct: example
23
#!/bin/bash
OPTIONS="Hello Quit“
select opt in $OPTIONS; do
if [ "$opt" = "Quit" ]
then
echo done
exit
elif [ "$opt" = "Hello" ]
then
echo Hello World
else
echo bad option
fi
done
~zhang/public_html/cs3130/Codes/select_ex

Next:
24
 More advanced bash scripting
 Array
 Function
 Inline input, or here document

Array
 Bash provides one-dimensional array variables
 Assign values to array:
array=( one two three )
files=( "/etc/passwd" "/etc/group" "/etc/hosts" )
limits=( 10 20 26 39 48)
 Access array element : ${array_name[index]}
 indexed using integers and are zero-based.
${array[1]}
 To access all items in arary: ${array_name[*]},
${array_name[@]}
 To access array length: len=${#x[@]}
25

To Iterate Through Array Values
26
#!/bin/bash
# declare an array called array and define 3 vales
array=( one two three )
for i in "${array[@]}"
do
echo $i
done

Exercise/Example
 Write a script that read a sequence of numbers
and save them in an array, print out the array
content and size.
 Usage: EchoNumber [file]
 If no file is specified, read from standard input
 Example script:
 LargestSmallest.sh
27

#!/bin/bash
i=0
if [ $# -eq 0 ]
then
echo "Enter the numbers, Ctrl-D to end";
cat > stdinput
set stdinput
fi
while read num
do
a[$i]=$num
i=$((i+1))
done < $1
echo Array is ${a[*]}, with ${#a[*]} numbers
28

Bash function
 Functions: to increase modularity and readability
 More efficient than breaking scripts into many
smaller ones
 Syntax to define a function:
function functionname()
{
commands . .
}
 function is a keyword which is optional.
 functionname is the name of the function
 No need to specify argument in ( )
 commands – List of commands to be executed I
 exit status of the function is exit status of last command
executed in the function body.
29

Function call
 Call bash function from command line or script
 $ functionname arg1 arg2
 When shell interprets a command line, it first looks
into the special built-in functions like break,
continue, eval, exec etc., then it looks for shell
functions.
 function defined in a shell start up file
(e.g.,.bash_profile ).
 available for you from command line every time you
log on
30

About functions
31
 Parameter passing: $1, $2, …
 Result returning
 Use echo command
 Through setting a variable
 return command: to return an exit status
#! /bin/bash
calsum(){
echo `expr $1 + $2`
}
x=1;y=2;
sum=`calsum $x $y`
calsum(){
sum=`expr $1 + $2`
}
x=1;y=2;
calsum $x $y
echo z=$sum

About functions
32
 Local variable: its scope is within the function
#! /bin/bash
calsumsqr(){
local sum=`expr $1 + $2`;
echo `expr $sum * $sum`
}
x=1;y=2;
z=`calsum $x $y`

Exercise/Example
 Write a function that check whether a user is log
on or not (CheckUser.sh)
function UserOnline()
{
if who | grep $1 ## UserOnline takes a parameter
then
return 0 ## 0 indicates success
else
return 1 ##1 for failure, i.e., offline
fi
}
if UserOnline $1 ## function’s return value as
condition/test
then
echo User $1 is online
else
echo User $1 is offline
33

Here document (inline document)
34
 A special way to pass standard input to a
command: here document, i.e., from shell script
itself
 Benefits: store codes and data together, easier to
maintain
#!/bin/bash
cat <<!FUNKY!
Hello
This is a here
Document
!FUNKY!
Here document starts with <<,
followed by a special string which is
repeated at the end of the document.
Note: the special string should be
chosen to be rare one.

Here document:2
35
 Example: 411 script that looks up a phone book
 Usage example: 411 joke
#!/bin/bash
grep “$*” << End
Dial-a-joke 212-976-3838
Dial-a-prayer 212-246-4200
Dial santa 212-976-141
End

Phone #
searching script
#!/bin/bash
cat > phone.pattern << PATTERNS
[^0-9][0-9]{10}$
[^0-9][0-9]{10}[^0-9]
[^0-9][0-9]{3}-[0-9]{3}-[0-9]{4}$
[^0-9][0-9]{3}-[0-9]{3}-[0-9]{4}[^0-9]
[^0-9][0-9]{3},[0-9]{4}$
PATTERNS
grep -f phone.pattern $*
rm phone.pattern ##no need to keep this file …
36

A case study:
bundle program
37
 Suppose a friend asks for copies of shell files in your
bin directory
$ cd ~/bin
$ for i in *.sh
> do
> echo ===== This is file $i =============
> cat $i
> done | mail yourfriend@hotmail.com
Pipeline & input/output redirection can be applied to for, while, until loop.

Make it better ?
38
 Construct a mail message that could
automatically unpack itself, i.e., to generate the
original files packed inside
 E.g., A shell script contains instructions for
unpacking, and the files content themselves
 Use here document mechanism

A bash script contains two files
39
#To unbundle, bash this file
echo file1 1>&2
cat >file1 <<'End of file1'
A
B
C
End of file1
echo file2 1>&2
cat >file2 <<'End of file2'
1
2
3
end of file2
What does this script do?
How to create such bundle file automatically?
Use a script, bundle.sh file1 file2 file3 …

Bundle script
40
#!/bin/bash
## write a shell script that contains files specified in
arguments
echo '#!/bin/bash'
echo ‘# To unbundle, bash this file’
for i ## without a list of items, loop through
## command line arguments
do
echo “echo $i 1>&2”
echo “cat >$i <<‘End of $i’”
cat $i
echo “End of $i”
done
codes/examples/bundle.sh
For homework 3, use bundle.sh to generate a hw3_bundle file, and submit it.

Summary
 Review of shell scripting
 Examples
 Array, function, inline document
41

Outline
42
 Coding standard: how to get good grades in lab
assignment
 Review of standard input/output/error
 How to redirect them ?
 Pipeline
 Review of bash scripting

Bash scripting: general hints
43
 Use echo command to trace (like cout, printf in
C/C++)
 Sometimes there are alternatives ways to do
things, choose one and remember it:
 $(( …)), and $[ … ]
 [[ ]] for test
 Be careful about typo, shell wont complain
variable not declared/assigned …
 The price of freedom
 A walk-through of basic bash scripting

Bash Scripting
44
 Variables
 Environment variable: affect behavior of shell
 User defined variable: default type is string, can
declare it to be other type
 Positional variables: used to pass command line
arguments to bash script
 Variable assignment:
x=10 ## assign value 10 to variable x, no space
around =
x=$x+1 ## add 1 to x’s value and assign to x
PATH=$PATH:.:~/bin
 To refer to a variable’s value, precede variable
name with $

A script that display positional
variable
45
echo All arguments: $*
echo Number of arguments: $#
echo Script name: $0
echo argument 1: $1
echo argument 2: $2
for arg in $*
do
echo argument $arg
done

arithmetic operation
46
 As variable’s default type is string, to perform
arithmetic operation, use the following syntax
$[$x+1] or $(($x+1))
 For simpler syntax: declare variable to be
numerical
declare –i x
x=$x*10+2
 Above are for integer arithmetic operations only ..

Command bc
47
 An arbitrary precision calculator
$ bc
3.14159*10^2
314.15900
130^2
16900
sqrt(1000)
31
scale=4
sqrt(1000)
31.6277
quit
An interactive calculator:
* user input shown in normal font,
* result shown in italics font
Internal variable scale:
* control the number of decimal points after decimal
point

bc in command line/script
48
 To evaluate an expression, simply send it using
pipe to bc
echo "56.8 + 77.7" | bc
 Write a script that read a Fahrenheit degree from
standard input, convert it to Celsius degree (up to
2 digits after decimal point):
C=(F-32)*5/9
 Base conversion, from base 10 (decimal) to base
16 (hexadecimal)
echo "obase=16; ibase=10; 56" | bc

Test/Conditions
49
 Any command or script, if it return 0, then test is
successful
if rm tmp.txt
then
echo file tmp.txt has been deleted
else
echo fail to remove file tmp.txt
Fi
 Use ! to negate

Test Condition
50
 Numerical comparisons
 -lt, -ne, -ge, …
 String comparision
 Pattern matching: using double brackets
 To test if first argument is “–” followed by a
number:
if [[ "$1" == -[0-9]* ]]
then
….

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