1. IT244 - Introduction to Linux / Unix Instructor: Bo Sheng
Shell (ch 5)
IT244 - Introduction to Linux / Unix
Instructor: Bo Sheng

2. Outline Command line syntax and processing
Standard I/O and device files
Redirection and pipes

3. Command Line Syntax Arguments command [arg1] [arg2] … [argn] RETURN
Separated by space
Could be optional ls
ls -l
cp hello hello.copy
command [arg1] [arg2] … [argn] RETURN

4. Command Line Syntax Arguments (options) ls –l, rm –i Combining options
ls -l -r = ls –lr
Option arguments
gcc -o hello hello.c

5. Command Line Syntax Non-option arguments starting with ‘-’
Create a file ‘-l’ and then list it
ls –l
ls ./-l, ls -- -l
Create a file ‘-i’ and then delete it
rm –i
rm ./-i, rm -- -i

6. Command Line Processing
e.g., /bin/ls
Arguments are processed
by programs, NOT the shell

7. Standard I/O

8. Standard I/O

9. Device Files The screen and keyboard as a file who, w cat
CTRL+D (EOF) to terminate

10. Device Files The screen and keyboard as a file
An example with two terminals
Use “who” to find out their device files,
e.g., /dev/pts/1 and /dev/pts/2
In terminal 2, type in
echo hello > /dev/pts/1
cat /dev/pts/1
Then type in terminal 1

11. Redirection Redirecting standard output ( > )
command [arguments] > filename

12. Redirection Redirecting standard output ( > ) Examples
echo hello world > hello
cat > sample
cat hello > sample
cat days months > sample

13. Redirection Redirecting standard output ( > ) Examples
ls > filelist
Append (>>)
echo append >> hello

14. Redirection Redirecting standard input ( < )
command [arguments] < filename

15. Pipes and Redirection command1 [arguments] | command2 [arguments]
command1 [arguments] > temp
command2[arguments] < temp
rm temp

16. Some New Utilities Translate (tr) tr abc ABC tr hld xyz < hello
tr “[A-Z]” “[a-z]” linux
Examples
cat month colors.1|tr “[A-Z]” “[a-z]” | sort

17. Some New Utilities Split directions (tee) tee filename
ls –l | tee filelist
cat colors.1 | tee file1 > file2
grep e colors.1 | tee /dev/pts/1 | sort

18. More Examples Use tr to replace or delete characters
echo “this is a test” > test
wc -c test
tr -d “ ” < test | wc –c

19. More Examples Redirection echo “***” >> hello
Insert a line before the first line
echo “***” > temp
cat temp hello > hello.new
mv hello.new hello
cat hello >> temp
mv temp hello
cat temp hello > hello ?

20. Filename Generation/Wildcards
“*” and “?”
“?” : single character
“*” : any number of characters (including 0)
ls colors.?
echo col*
ls hello*

21. Filename Generation/Wildcards
Examples
echo ?????
echo ~/.*
cat hello*

22. Filename Generation/Wildcards
“[]” for range
echo [aeiou]*
cat colors.[135]
echo [a-z]*
echo *[a-l]
“^” for “not”
echo *[^a-z]
echo [^a-o]*

23. Execute Commands Foreground and background jobs
cp ~shengbo/it244/exetest .
./exetest (CTRL+C to terminate)
./exetest & (running in background)
jobs

24. Execute Commands Foreground and background jobs Multitasking
One foreground in a terminal
Only foreground gets input from keyboard
Multitasking

25. Execute Commands
Job number / PID number
Job number
Process ID

26. Execute Commands
Job number / PID number
Job number
Process ID

27. Execute Commands Suspend a foreground job ./exetest CTRL+Z jobs
Different from a running background job

28. Execute Commands Resume a suspended job In the background
bg [%job_number]
In the foreground
fg [%job_number]
Bring background job to foreground

29. Execute Commands Abort a job Foreground Background CTRL+C
kill process_ID
kill %job_number
tail –f hello &