1. The UNIX Shell Learning Objectives:
To give detailed description for using commands in Unix Shell
To introduce more advanced techniques for handling complicate commands in Unix Shell
To understand the the usage of background jobs & shell switching
To learn more about pattern matching

2. How Does the Shell Find a Command?
The shell searches a list of directories for an executable file with the same name.
$ echo $path shows you the current path
The list of directories is stored in the PATH variable for Bourne shells and in the path array for csh/tcsh
$ PATH=/usr/local/bin:$PATH sh
% set path=(/usr/local/bin $path) csh, tcsh
If there is a match in more than one directory, the shell uses the first one it finds.
It is usually set in your .cshrc file in your home directory

3. Alias
The C Shell has the alias command, which allows you to create command shortcuts.
$ alias dir "ls -F"
$ alias rm "rm -i"
$ alias + "chmod u+x *"
$ alias - "chmod u-x *"
$ alias 111 "cd ~horner/111"
$ pwd
/bin
$ 111
/homes/horner/111
If you put the alias commands in your .cshrc file, you can use them every time you login.

4. Tee A special command called tee acts like a T-joint in plumbing:
$ who
horner pts/3 Feb 11 10:23 (csnt1.cs.ust.hk)
horner pts/0 Feb 11 11:57 (csz096.cs.ust.hk)
$ who | sort | tee sortedwho | wc -l 2
$ cat sortedwho $
In this example, the output of sort is placed in a file “sortedwho“ and piped to wc -l, which counts the number of lines.

5. Background Jobs
A simple command or pipeline can be put into the background by following it with the “&” character:
$ sort names > names.sort &
[1] 3236
The shell will print the process ID (PID), and a job number (1, in this case).
Put a job in the background by typing “CTRL-Z”
$ ypcat passwd | sort >passwd.sort ^Z
Suspended
The job is suspended - not running - until you either place it in the background using bg:
$ bg
[1] ypcat passwd | sort > passwd.sort &
or back to the foreground using fg:
$ fg
ypcat passwd | sort >passwd.sort

6. Jobs You can stop a job with the kill command:
$ ypcat passwd | sort > passwd.sort &
[1]
$ kill %1
[1] Terminated ypcat passwd |
Exit 2 sort > passwd.sort
The “%1” means “job #1”. You can also use the PID.
The ps command is the main way to find out about jobs:
[1]
$ ps
PID TTY TIME CMD
3477 pts/0 0:00 sort
1401 pts/0 0:01 csh
3476 pts/0 0:01 ypcat $

7. Combining Commands (1)
Multiple pipelines can be input on one command line by separating them with semicolons.
When entering a long command, use a backslash (\) to continue the command on the next line.
$ date; sort names; \
who
Thu Feb 11 19:40:28 HKT 1999
Bill Clinton
Bill Gates
Monica Lewinski
horner pts/ Feb 11 10:23 (csnt1.cs.ust.hk)
horner pts/ Feb 11 19:11 (csz096.cs.ust.hk)

8. Combining Commands (2)
Commands can be grouped together using parentheses
There are two main reasons to group commands:
To create a “single command” out of a group of commands (especially useful before a pipe):
$ (cat names; head -2 names) | wc –l
# if names has 8 lines, what does this line return?
To run a set of commands in their own subshell (especially when trying to limit the effect of a cd command):
$ (cd secret; ls | wc -l); ls | wc -l 3 25
This line has the effect of counting the files in secret, and then counting the files in the current directory.
Question: what does this do?
cd ; cd 111; (cd ..;cd 122); cd ..

9. cut and tr
cut -cx-y cuts characters from position x to position y (the first position is 1).
-r--r--r horner cs Feb 12 16:00 letter1
What does this do?
ls -l | sort +4 | tail -1 | cut -c55-70
The following command returns the user name
who am i | cut -f1 -d' ‘
-f1 specifies the first field
Field is defined by the delimiter ‘ ‘
The following command translates all lower case to upper case
tr “[a-z]” “[A-Z]” filename
tr means translate
To compress all spaces tr -s '[ ]*' ' ‘
Who | tr –s ‘[ ]*’ ‘ ‘ | cut –d’ ‘ –f2

10. Patterns
The pattern “[abcd]” matches any single one of the enclosed characters.
The following “ls” command lists any file whose name start with “i” or “l” followed by any
other characters
$ ls [il]*
it it ith letter1 letter4 $
* matches anything
The notation “[a-z]” matches any lowercase letter once.
The notation “[0-9]” matches any digit character once.
The notation “[0-59]” matches any the digit characters 0, 1, 2, 3, 4, 5, and 9.
$ ls letter*
letter1 letter4
$ ls letter[0-35]
letter1
$ ls letter[0-24]

11. More Pattern Matching – grep (1)
grep finds all matches of a pattern in a file :
To build a pattern, use the following:
^ start of line $ end of line
. any character \ quote next character
* match zero or more + match one or more
? match zero or one
[aeiou0-9] match a,e,i,o,u, and 0 thru 9
[^aeiou0-9] match anything but a,e,i,o,u, and 0 thru 9
‘a*’ match zero or more occurrences of ‘a’
‘a+’ match one or more occurrences of ‘a’ (egrep)

12. More Pattern Matching – grep (2)
$ cat names
Bill Gates
Jacky Gs
James Bill
J. Jones
$ grep '^Bill’ names
$ grep 'Bill$’ names
$ grep ’J...s’ names
$ grep 'G.*s' names
Bill Gates
Jacky Gs
$ grep 'G.+s' names
$ egrep 'G.+s' names
$ egrep 'G.s' names
$ egrep 'G.?s' names
J. Jones
$ grep 'J\.' names
Some versions of grep cannot process ?+

13. More Pattern Matching – grep (3)
$ cat names
Bill Gates
Jacky Gs
James Bill
J. Jones
$ grep 'Ja[cm]' names
$ grep 'J[^a]' names
$ grep ’[t-y]' names
$ grep -in bill names
1:Bill Gates
3:James Bill
$ grep -v Bill names
Jacky Gs
J. Jones
$ grep -l Bill n*
names
$ grep -c Bill names 2
-i ignores case
-n shows line number
-v means line *not* containing pattern
-l shows *filename* containing pattern
-c shows matching count

14. How to do this?
Find all lines in ‘file1’ that does not contain any vowels
Hint: use –v option
Find all lines in ‘file1’ that contains only vowels.
Hint: use ^string$
Find all lines in file1 with length 7 and ‘a’ as the fourth character
Find all lines that contain ‘a’, ‘c’, and ‘e’, in that order