02 Shell Intro

8/8/2019 02 Shell Intro

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Advanced UNIX (Shell)

Objectives to supplement the Introduction to UNIX

slides with extra information about the Shell


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Overview1. Redirection

2. Pipes

3. Background Jobs

4. Filename Generation


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command

standard input

standard

output

1. Redirection

Command I/O is stream-based:


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$ catThis is a line of text.This is a line of text.

Cat keeps copying lines of textCat keeps copying lines of text

until you press control-D at theuntil you press control-D at the

beginning of a line.beginning of a line.

$

control-D

You type a line;

it is echoed


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command

standard input

standard

output file

RedirectOutput Use > to redirect standard output

to a file:


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$ cat > sample.txtThis text is being entered at the keyboard.

Cat is copying it to a file.Press control-D to indicate the

end of file.

$

$ cat file1.c file2.c file3.c > all-files.c

control-D


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command

standard

input

standard

output

Redirect Input Use < to redirect standard input

from a file:

file


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$ cat < supply_orders

2000 sheets letterhead ordered: 10/7/971box masking tape ordered: 10/8/97

$

$ cat supply_orders

$ mail [email protected] < letter.txt


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D

angers Bad:

$ cat orange pear > orange

cat: input orange is output

see noclobber in C Shell

Good:$ cat orange pear > temp$ mv temp orange


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Appending Output to a File Use >> to append:

$ date > whoson

$ cat whoson

Fri May 29 09:24:19 GMT 2000

$ who >> whoson

$ cat whoson

Fri May 29 09:24:19 GMT 2000

jenny tty02 May 29 07:21

ad tty06 May 28 11:01

$


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command1

standardinput

standardoutput

command2

2

. Pipes Use a pipe to connect standard

output of one command to

standard input of another:


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Use the | operator between commands:

$ command 1| command2

Same as:

$ command1> temp$ command2 < temp

$ rm temp


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$ ls | more

$ who | grep ad

ad tty06 May 23 10:31

$ who | sortad tty06 May 23 10:31jenny tty02 May 21 15:29scott tty03 May 23 09:02

Same as:$ who > temp

$ sort < temp or $ sort temp


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Filters A filter is a command that modifies

its standard input, putting the

changes onto its standard output:

$ who | sort | lpr

$ ps | grep ad


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The tee Command

Passes its input through to standard output

unchanged.Also saves input into a file:

command1

standardinput

standardoutput

command2tee

file


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$ who | tee who.out | grep ad

ad tty06 May 23 10:31

$ cat who.out

jenny tty02 May 21 15:29

ad tty06 May 23 10:31

scott tty03 May 23 09:02


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3. Background Jobs

A normal command executes in the

foreground: you waituntil it finishes before

another command can be typed.

Commands (jobs) can execute in the

background.No need to waitfor them before

another command is typed.


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Background jobs end with a &:

$ gcc big-program.c &

1466

$ ls -l | lpr &

1467

$ vi report.txt


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Killing a Background Job Cannot type control-C

Use killand the process ID (PID):$ kill 1466

Use psto list PIDs:

$ ps

PID TT STAT TIME COMMAND

1466 03 S 0:05 gcc big-program.c

1467 03 S 0:04 ls -l | lpr

1524 03 R 0:03 ps

$


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4. Filename Generation

Commands involving filenames (e.g.cat, ls)

can include special characters in the

filenames.called metacharacters

three kinds:

?

*

[...]


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The ? Special Character

? matches any single character

$ lsmem memo12 memo9 memoalex newmemo5memo memo5 memoa memos

$ ls memo?

memo9 memo5 memoa memos

$ lpr memo?

continued


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$ ls

7may4report may14reportmay4report.79

mayqreport may.report may4reportmay_report mayreport

$ ls may?report

mayqreport may.report may4reportmay_report


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The * Special Character

* matches any sequence of characters

(0 or more characters)

$ ls

amemo memo memoa memosallyuser.memo mem memo.0612

memorandum sallymemo

$ ls memo*memo memoa memosally memo.0612

memorandum

continued


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$ ls *.txt

$ lpr *.txt

$ ls *.c$ cat *.c > all-files

$ more all-files$ rm *.c

$ mv all-files all-files.c


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The [...]Special Characters

Match against any single character given inside

[...]

Can include - to give a range

$ ls

part1.txt part2.txt part3.txt part4.txt part5.txt

$ lpr part[135].txt$ cat part[1-3].txt

continued


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Useful Ranges

[a-z] any letter between a and z

[A-Z] any letter between A and Z

[0-9] any digit betwwn 0 and 9

Can combine:

[a-z,0-9]

continued


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$ lspart0 part1 part2 part3 part4 ...

part32 part33 part34 part35

$ ls part[0-9]$ ls part[12][0-9]

$ ls part3[0-5]


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Combining Special Characters

$ ls [a-m]*

$ ls *[x-z]

$ lpr p*[0-9].c &

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