Unix Shell Scripting Basics

Agenda
What is a shell? A shell script?
Introduction to bash
Running Commands
Applied Shell Programming

What is a shell?
INPUT
shell
OUTPUT ERROR

What is a shell?
Any Program
But there are a few popular shells…

Bourne Shells
 /bin/sh
 /bin/bash
“Bourne-Again Shell”
Steve Bourne

Other Common Shells
C Shell (/bin/csh)
Turbo C Shell (/bin/tcsh)
Korn Shell (/bin/ksh)

An aside: What do I mean by /bin ?
C Shell (/bin/csh)
Turbo C Shell (/bin/tcsh)
Korn Shell (/bin/ksh)

An aside: What do I mean by /bin ?
 /bin, /usr/bin, /usr/local/bin
 /sbin, /usr/sbin, /usr/local/sbin
 /tmp
 /dev
 /home/borwicjh

What is a Shell Script?
A Text File
With Instructions
Executable

What is a Shell Script?
% cat > hello.sh <<MY_PROGRAM
#!/bin/sh
echo ‘Hello, world’
MY_PROGRAM
% chmod +x hello.sh
% ./hello.sh
Hello, world

What is a Shell Script? A Text File
#!/bin/sh
MY_PROGRAM
% chmod +x hello.sh
% ./hello.sh
Hello, world

An aside: Redirection
 cat > /tmp/myfile
 cat >> /tmp/myfile
 cat 2> /tmp/myerr
 cat < /tmp/myinput
 cat <<INPUT
Some input
INPUT
 cat > /tmp/x 2>&1
INPUT
env
OUTPUT ERROR
0
1 2

What is a Shell Script? How To Run
#!/bin/sh
MY_PROGRAM
% chmod +x hello.sh
% ./hello.sh
Hello, world

What is a Shell Script? What To Do
#!/bin/sh
MY_PROGRAM
% chmod +x hello.sh
% ./hello.sh
Hello, world

What is a Shell Script? Executable
#!/bin/sh
MY_PROGRAM
% chmod +x hello.sh
% ./hello.sh
Hello, world

What is a Shell Script? Running it
#!/bin/sh
MY_PROGRAM
% chmod +x hello.sh
% ./hello.sh
Hello, world

Finding the program: PATH
% ./hello.sh
echo vs. /usr/bin/echo
% echo $PATH
/bin:/usr/bin:/usr/local/bin:
/home/borwicjh/bin
% which echo
/usr/bin/echo

Variables and the Environment
% hello.sh
bash: hello.sh: Command not found
% PATH=“$PATH:.”
% hello.sh
Hello, world

An aside: Quoting
% echo ‘$USER’
$USER
% echo “$USER”
borwicjh
% echo “””
”
% echo “deacnetsct”
deacnetsct
% echo ‘”’
”

Variables and the Environment
% env
[…variables passed to sub-programs…]
% NEW_VAR=“Yes”
% echo $NEW_VAR
Yes
% env
[…PATH but not NEW_VAR…]
% export NEW_VAR
% env
[…PATH and NEW_VAR…]

How to Learn
 man
 man bash
 man cat
 man man
 man –k
 man –k manual
 Learning the Bash Shell, 2nd
Ed.
 “Bash Reference” Cards
 http://www.tldp.org/LDP/abs/html/

Continuing Lines:
% echo This
Is
A
Very
Long
Command Line
This Is A Very Long Command Line
%

Exit Status
$?
0 is True
% ls /does/not/exist
% echo $?
1
% echo $?
0

Exit Status: exit
% cat > test.sh <<_TEST_
exit 3
_TEST_
% chmod +x test.sh
% ./test.sh
% echo $?
3

Logic: test
% test 1 -lt 10
% echo $?
0
% test 1 == 10
% echo $?
1

Logic: test
test
[ ]
 [ 1 –lt 10 ]
[[ ]]
 [[ “this string” =~ “this” ]]
(( ))
 (( 1 < 10 ))

Logic: test
 [ -f /etc/passwd ]
 [ ! –f /etc/passwd ]
 [ -f /etc/passwd –a –f /etc/shadow ]
 [ -f /etc/passwd –o –f /etc/shadow ]

An aside: $(( )) for Math
% echo $(( 1 + 2 ))
3
% echo $(( 2 * 3 ))
6
% echo $(( 1 / 3 ))
0

Logic: if
if something
then
:
# “elif” a contraction of “else if”:
elif something-else
then
:
else
then
:
fi

Logic: if
if [ $USER –eq “borwicjh” ]
then
:
# “elif” a contraction of “else if”:
elif ls /etc/oratab
then
:
else
then
:
fi

Logic: if
# see if a file exists
if [ -e /etc/passwd ]
then
echo “/etc/passwd exists”
else
echo “/etc/passwd not found!”
fi

Logic: for
for i in 1 2 3
do
echo $i
done

Logic: for
for i in /*
do
echo “Listing $i:”
ls -l $i
read
done

Logic: C-style for
for (( expr1 ;
expr2 ;
expr3 ))
do
list
done

Logic: C-style for
LIMIT=10
for (( a=1 ;
a<=LIMIT ;
a++ ))
do
echo –n “$a ”
done

Logic: while
while something
do
:
done

Logic: while
a=0; LIMIT=10
while [ "$a" -lt "$LIMIT" ]
do
echo -n "$a ”
a=$(( a + 1 ))
done

Counters
COUNTER=0
while [ -e “$FILE.COUNTER” ]
do
COUNTER=$(( COUNTER + 1))
done
Note: race condition

Reusing Code: “Sourcing”
% cat > /path/to/my/passwords <<_PW_
FTP_USER=“sct”
_PW_
% echo $FTP_USER
% . /path/to/my/passwords
% echo $FTP_USER
sct
%

Variable Manipulation
% FILEPATH=/path/to/my/output.lis
% echo $FILEPATH
/path/to/my/output.lis
% echo ${FILEPATH%.lis}
/path/to/my/output
% echo ${FILEPATH#*/}
path/to/my/output.lis
% echo ${FILEPATH##*/}
output.lis

It takes a long time to
become a bash
guru…

Reasons for Running Programs
Check Return Code
 $?
Get Job Output
 OUTPUT=`echo “Hello”`
 OUTPUT=$(echo “Hello”)
Send Output Somewhere
 Redirection: <, >
 Pipes

Pipes
Lots of Little Tools
echo “Hello” |
wc -c
INPUT
echo
OUTPUT ERROR
0
1 2
INPUT
wc
OUTPUT ERROR
0
1 2
A Pipe!

Email Notification
% echo “Message” |
mail –s “Here’s your message”
borwicjh@wfu.edu

Dates
% DATESTRING=`date +%Y%m%d`
% echo $DATESTRING
20060125
% man date

FTP the Hard Way
ftp –n –u server.wfu.edu <<_FTP_
user username password
put FILE
_FTP_

FTP with wget
 wget
ftp://user:pass@server.wfu.edu/file
 wget –r
ftp://user:pass@server.wfu.edu/dir/

FTP with curl
curl –T upload-file
-u username:password
ftp://server.wfu.edu/dir/file

Searching: grep
% grep rayra /etc/passwd
% grep –r rayra /etc
% grep –r RAYRA /etc
% grep –ri RAYRA /etc
% grep –rli rayra /etc

Searching: find
% find /home/borwicjh
-name ‘*.lis’
[all files matching *.lis]
% find /home/borwicjh
-mtime -1 –name ‘*.lis’
[*.lis, if modified within 24h]
% man find

Searching: locate
% locate .lis
[files with .lis in path]
% locate log
[also finds “/var/log/messages”]

Make Your Life Easier
TAB completion
Control+R
history
cd -
Study a UNIX Editor

pushd/popd
% cd /tmp
% pushd /var/log
/var/log /tmp
% cd ..
% pwd
/var
% popd
/tmp

Monitoring processes
ps
ps –ef
ps –u oracle
ps –C sshd
man ps

“DOS” Mode Files
#!/usr/bin/bash^M
FTP transfer in ASCII, or
dos2unix infile > outfile

sqlplus
JOB=“ZZZTEST”
PARAMS=“ZZZTEST_PARAMS”
PARAMS_USER=“BORWICJH”
sqlplus $BANNER_USER/$BANNER_PW << _EOF_
set serveroutput on
set sqlprompt ""
EXECUTE WF_SATURN.FZ_Get_Parameters('$JOB',
'$PARAMS', '$PARAMS_USER');
_EOF_

sqlplus
sqlplus $USER/$PASS @$FILE_SQL
$ARG1 $ARG2 $ARG3
if [ $? –ne 0 ]
then
exit 1
fi
if [ -e /file/sql/should/create ]
then
[…use SQL-created file…]
fi
 Ask Amy Lamy! 

Passing Arguments
% cat > test.sh <<_TEST_
echo “Your name is $1 $2”
_TEST_
% chmod +x test.sh
% ./test.sh John Borwick ignore-
this
Your name is John Borwick

INB Job Submission Template
$1: user ID
$2: password
$3: one-up number
$4: process name
$5: printer name
% /path/to/your/script $UI $PW
$ONE_UP $JOB $PRNT

Scheduling Jobs
% crontab -l
0 0 * * * daily-midnight-job.sh
0 * * * * hourly-job.sh
* * * * * every-minute.sh
0 1 * * 0 1AM-on-sunday.sh
% EDITOR=vi crontab –e
% man 5 crontab

Other Questions?
Shells and Shell Scripts
bash
Running Commands
bash and Banner in Practice

Unix Shell Scripting Basics

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