1. Shell Script Examples

2. A shell script is… A series of OS commands for execution
Stored in a text file
#!/bin/sh
rm -f /tmp/listing.tmp > /dev/null 2>&1
touch /tmp/listing.tmp
ls -l [a-z]*.doc | sort > /tmp/listing.tmp
lpr -Ppostscript_1 /tmp/listing.tmp
rm -f /tmp/listing.tmp

3. Components of a script Shell in use (sh, bash, csh) #!/bin/sh
rm -f /tmp/listing.tmp > /dev/null 2>&1
touch /tmp/listing.tmp
# This is a comment
ls -l [a-z]*.doc | sort > /tmp/listing.tmp
lpr -Ppostscript_1 /tmp/listing.tmp
rm -f /tmp/listing.tmp
Command
Comment

4. How to invoke a script Correct way Simple way
$ /bin/bash my_script arg_1 arg_2
Simple way
$ my_script arg_1 arg_2
The first line specifying the shell must be provided in simple way

5. Definitions Blank = chunk of tab or space
Name = sequence of ASCII letters, digits, underscores, beginning with a letter or underscore
Argument = string supplied on command-line

6. Example (argument) (1) #!/bin/sh ##############################
echo "Script name is [$0]"
echo "First argument is [$1]"
echo "Second argument is [$2]"
echo "This process ID is [$$]"
echo "This argument count is [$#]"
echo "All arguments

7. Example (argument) (2) :~> my_script.sh bhecker 1 university
Script name is [my_script.sh]
First argument is [bhecker]
Second argument is [1]
This process ID is [5401]
This argument count is [3]
All arguments [bhecker 1 university]

8. Filename meta characters*
Match any string of zero or more characters ?
Match any single character
[abc...]
Match any one of the enclosed characters; a hyphen can specify a range (e.g., a-z, A-Z, 0–9)
[!abc...]
Match any character not enclosed as above ~
Home directory of the current user
~name
Home directory of user name ~+
Current working directory ($PWD) ~-
Previous working directory ($OLDPWD)

9. Simple regular expressions (Korn shell)
?(pattern)
Match zero or one instance of pattern
*(pattern)
Match zero or more instances of pattern
+(pattern)
Match one or more instances of pattern
@(pattern)
Match exactly one instance of pattern
!(pattern)
Match any strings that don't match pattern
Pattern = sequence of patterns separated by “|”

10. Example (meta characters)
List files having prefix new
$ ls new*
Cat files having prefix ch and one more letter
$ cat ch?
Vi files starting by letters from D to E
$ vi [D-R]*
Print files not *.o and core (Korn shell)
$ pr !(*.o|core) | lp

11. Quoting "" Everything taken literally, except ''
$ (variable substitution)
` (command substitution)
“ (ending mark) ''
Everything taken literally \
Character following \ taken literally

12. Example (quoting) $ echo 'my class is "unix and tools"'
$ echo "Well, isn't that \"good\" ?"
Well, isn't that "good" ?
$ echo "You have `ls | wc –l` files in `pwd`"
You have 34 files in /home/bhecker
$ echo "The value of \$x is $x"
The value of $x is 100

13. Variables (1) var=value… Set variable to value ${var} Use value of var
Use var if set, otherwise, use value
${var:=value}
Use var if set, otherwise, user value and assign it to var
${var:?value}
Use var if set, otherwise, print value and exit
${var:+value}
Use value of var is set, otherwise use nothing
${#var}
Use the length of var
${#*} or
Use the number of positional arguments

14. Variables (2) ${var#pattern}
Use value of var after removing pattern from the left. Remove shortest matching
${var##pattern}
Same as #pattern. Remove longest matching
${var%pattern}
Use value of var after removing pattern from the right. Remove shortest matching
${var%%pattern}
Same as %pattern. Remove longest matching

15. Command forms cmd1 ; cmd2 Multiple commands on the same line
Commands as a group in current shell
(cmd1 ; cmd2)
Commands as a group in a subshell
cmd1 | cmd2
Pipe
cmd1 `cmd2`
Command substitution
cmd1 $(cmd2)
POSIX Command substitution (nesting is allowed)
cmd $((expression))
POSIX shell arithmetic substitution
cmd1 && cmd2
AND; cmd1, then cmd2 if (cmd succeeds)
cmd1 || cmd2 OR
! cmd
NOT; change exit status

16. Example (command forms)
$ nroff file > file.txt &
Format in the background
$ cd; ls
Execute sequentially
$ (date; who; pwd) > logfile
All output is redirected
$ sort file | pr -3 | lp
Sort file, page output, then print
$ vi 'grep -l ifdef *.c'
Edit files found by grep
$ grep XX file && lp file
Print file if it contains the pattern;
$ grep XX file || echo "XX not found"
otherwise, echo an error message

17. Simple commands sort Sort lines grep Search for regular expressions
basename
Get file name from path string
dirname
Get directory name from path string
cut
Chop up a text by strings or characters
[(test)]
Predicate or conditional processor
tr 'a' 'b'
Transform characters
expr
Simple arithmetic processor
eval
Evaluate variables
date
Create date strings
head/tail
Access lines in files

18. Example (script) (1) #!/bin/bash
alphabet="a b c d e" # Initialize a string
count= # Initialize a counter
for letter in $alphabet # Set up a loop control
do # Begin the loop
count=‘expr $count + 1’ # Increment the counter
# Display the result
echo "Letter $count is [$letter]"
done

19. Example (script) (2) alphabet="a b c d e" # Initialize a string
count= # Initialize a counter
while [ $count -lt 5 ] # Set up a loop control
do # Begin the loop
count=‘expr $count + 1’ # Increment the counter
# Position of next letter
position=‘bc $count + $count – 1’
letter=‘echo "$alphabet" | cut -c$position-$position’ # Get next letter
# Display the result
echo "Letter $count is [$letter]"
done