Sperimentazioni I LINUX commands tutorial - Part II

(1)

Sperimentazioni I

LINUX commands tutorial - Part II

gruppo B - 27/10/2008 gruppo C - 28/10/2008 gruppo A - 29/10/2008

A. Garfagnini

Università degli studi di Padova

October 27, 2008

Streams Pipelines Create, monitor and kill processes

Streams and I/O Redirection

Pipelines

Create, monitor and kill processes

(2)

The BASH I/O Streams

• All the UNIX shells use three standard I/O streams:

stdout , thestandard output streamwhich displays output from commands.

stderr , thestandard error streamwhich displays error output from streams.

stdin , thestandard input streamwhich provides input to commands.

Stream File descriptor

stdin 0

stdout 1

stderr 2

• Input streams provide input to programs, usuallyfrom terminals.

• Output streams print text characters, usually to terminals.

Redirecting output

• There are two ways to redirect output:

n>

redirects output fromfile descriptor n to a file.

• You must have write permission to the file.

• If the file does not exist, it is created.

• If the file exists, theexisting content is lost without any warning.

n >>

redirects output fromfile descriptor n to a file.

• You must have write permission to the file.

• If the file does not exist, it is created.

• If the file exists, theoutput is appended to the existing file.

(3)

Redirecting output streams - examples

No redirection

$ ls a* z*

/bin/ls: z*: No such file or directory a1 a2 a3 a4 a5 a.out* a.ps

stdoutredirection

$ ls a* z* >stdout.txt

/bin/ls: z*: No such file or directory

$ cat stdout.txt a1

a2 a3 a4 a5 a.out*

a.ps

stderrredirection

$ ls a* z* 2>errori.txt

a1 a2 a3 a4 a5 a.out* a.ps

$ cat errori.txt

both output streams redirected

$ ls a* z* >stdout.txt 2>>errori.txt

$ cat errori.txt

/bin/ls: z*: No such file or directory /bin/ls: z*: No such file or directory

Redirecting both streams to the same file

• Sometimes both output streams have to be redirectedto one file

• The procedure is often used for automated processes or in background jobs.

• Three possibilities:

1. command 1> output.log 2> output.log 2. command > output.log 2>&1

3. command &> output.log

• To append output to a file, replace> with >>

• Q: How to ignore output streams ?

• A: redirect the appropriate stream to /dev/null

Ex: Ignoring error output stream

$ ls a* z* 2>/dev/null

a1 a2 a3 a4 a5 a.out* a.ps

(4)

Input redirection

• stdinstream can be redirected from a file, using the< operator stdin/stdout redirect example

$ ls -1 > list.out

$ cat list.out a1

a2 a3

$ sort -r < list.out a3

a2 a1

Redirect stdout to list.out

All entries in ascending order

Process input from file with sort giving a reverse ordering

The cat command

• Thecat command, short for catenate, allows to display the contents of a fileon stdout:

$ cat list.out a1

...

a3

• Thecat command takes input from stdin if you do not specify a file name; it keeps reading from stdinuntil the end-of-file.

(ctrl-dis used to signal end-of-file).

Creating a file with cat

$ cat >list2.out a1

...

a3

$ Ctrl-d is pressed

(5)

Input redirection with here-document

• The here-document is another form of input redirection

• It uses the<<along with a word, such as END fora marker to indicate the end of input.

[agarfa]$ cat«END>ex-here.sh

> cat «-EOF

> apple

> EOF

> END

[agarfa]$ cat ex-here.sh cat «-EOF

apple pear EOF

[agarfa]$ . ex-here.sh apple

pear

source the script,

i.e. run in the current shell context

• It isoften used in script fileswhere there isno otherway to indicatewhich lines should be treated asinput.

Input redirection summary

> file Direct standard output to file

< file Take standard input from file

>> file Direct standard output to file; append to file if it exists

<< label Here-document

n> file Direct file descriptor n to file n< file Take file descriptor n from file

n >> file Direct file descriptor n to file; append to file if it exists n>& Duplicate standard output to file descriptor n

n<& Duplicate standard input from file descriptor n

n>&m File descriptor n becomes a copy of the output file descriptor n<&m File descriptor n becomes copy of the input file descriptor

&>file Directs standard output and standard error to file

(6)

Pipelines

• Text filteringis the process of taking an input stream of text and performing some conversion before sending it to an output stream

• Filtering is done constructing apipelineof commands where the output from one command ispipedorredirected as input to the next:

command1 | command2 [| command3 ...]

[agarfa]$ ls *a *z | sort /bin/ls: z*: No such

file or directory a1

a2

[agarfa]$ ls *a *z 2>&1 | sort a1

a2

• N.B. pipelines only pipe stdout to stdin!

• if stderrhas been redirected tostdout, both streams will be piped.

• One advantage of pipes on LINUX and UNIX is thatthere is no

intermediate file involved: thestdout of the first command is sent directly to the second command.

head or tail ... and wc

• While cat allows to concatenate files and print them on the standard output

head output thefirst part of files (10 lines by default)

• head -n K prints thefirst K linesof a file;

• head -c B prints thefirst B bytesof a file;

tail output thelast part of files (10 lines by default)

• tail -n K prints thelast K linesof a file;

• tail -c B prints thelast B bytesof a file;

wc prints newline, word and byte counts for each file

• wc -c print the byte counts;

• wc -l print the newline counts;

• wc -w print the wordcounts;

(7)

Finding text in files

• Thegrepcommand print lines matching a pattern grep [OPTIONS] PATTERN [FILE...]

• grepsearches the named input FILEs, or standard input if no files are named, for lines containing a match to the givenPATTERN.

• grep -i ignore case distinctions in both the PATTERN and the input files.

• grep -n prefix each line of output with the 1-based line number within its input file.

[agarfa]$ grep iostream *.cxx primo.cxx:#include <iostream>

secondo.cxx:#include <iostream>

[agarfa]$ grep -n iostream *.cxx primo.cxx:1:#include <iostream>

secondo.cxx:1:#include <iostream>

[agarfa]$ ls -l | grep cxx

-rw-r-r- 1 agarfa fisica 100 Oct 21 12:27 primo.cxx -rw-r-r- 1 agarfa fisica 100 Oct 19 22:54 secondo.cxx

Foregroud and background jobs

• When you run a command in a terminal window, you are running it in the foreground.

• The Bash shell has asuspend key,Ctrl-z. Pressing this key combination, you get the terminal prompt again.

• The clock is still on your destop but has stopped running.

• It can be restarted with the fg command

• fg brings the job right back to the foreground, but you no longer have a shell prompt.

• Thebg command continues running your job in backgorund and giving back the terminal prompt

[agarfa]$ xclock -d -update 1

[2]+ Stopped xclock -d -update 1 [agarfa]$ fg %2

xclock -d -update 1

[1]+ Stopped xclock -d -update 1 [agarfa]$ bg %1

[1]+ xclock -d -update 1 &

(8)

Using &

• To start a newjob in background, add a & character at the end of the command

• The message shows a job number and a process id (PID).

• With thejobs command is possible to find out what jobs are running

• The-l option prints PIDs and the plus sign(+) beside the job number indicates that is the current job

[agarfa]$ xclock -d -update 2 &

[1] 29696

[agarfa]$ jobs -l

[1]+ 29696 Running xclock -d -update 1 &

ps : inspecting process status information

• Theps command accepts zero or more PIDs as argument and displays the associated process status

• Using pswith no options will list all processes that have our terminal as their controlling terminal

[agarfa]$ jobs -l [1] 29696

[agarfa]$ ps 29696

PID TTY STAT TIME COMMAND

29696 pts/6 S 0:00 xclock -d -update 1 [agarfa]$ ps

PID TTY TIME CMD

27082 pts/6 00:00:00 bash 29696 pts/6 00:00:00 xclock 30170 pts/6 00:00:00 ps

(9)

More process status information

• Several options give control of how much information is displayed with the process status:

-f : full -j : jobs -l : long

--forest : display the commands in a tree hierarcy

[agarfa]$ ps -l

F S UID PID PPID C PRI NI ADDR SZ WCHAN TTY TIME CMD 0 S 8266 422 8479 0 80 0 - 1519 - pts/1 00:00:00 bash 0 R 8266 822 422 0 80 0 - 607 - pts/1 00:00:00 ps [agarfa]$ ps -j

PID PGID SID TTY TIME CMD 2388 2388 27082 pts/6 00:00:00 ps 27082 27082 27082 pts/6 00:00:00 bash [agarfa]$ ps --forest

PID TTY TIME CMD 422 pts/1 00:00:00 bash 764 pts/1 00:00:00 \_ ps

Displaying other processes

• The-xoption displays processes without a controlling terminal

• The-eoption displays dinformation foreveryprocess

• Many options possible, get a brief summary withps --help

[agarfa]$ ps afx # Use BSD syntax PID TTY STAT TIME COMMAND

2 ? S< 0:00 [kthreadd]

...

1 ? Ss 0:01 /sbin/init

...

5852 ? Ss 0:00 /usr/sbin/gdm 5855 ? S 0:00 \_ /usr/sbin/gdm

8057 tty7 SLs+ 24:26 \_ /usr/bin/X :0 -br -audit 0 -auth /var/lib/gdm/:0.Xauth -nolisten tc

8087 ? Ss 0:00 \_ /bin/sh /etc/xdg/xfce4/xinitrc -- /etc/X11/xinit/xserverrc

8175 ? Ss 0:00 \_ /usr/bin/seahorse-agent

--execute startxfce4

8191 ? S 0:50 \_ xscreensaver -no-splash

8196 ? Sl 0:35 \_ /usr/bin/xfce4-session

8253 ? S 0:02 | \_ /usr/lib/xfce4/[...] socket_i

8479 ? Ssl 0:27 | | \_ gnome-terminal

8485 ? S 0:00 | | | \_ gnome-pty-helper

...

26523 pts/4 Ss 0:00 | | | \_ bash

(10)

top

• Thetopcommand displays a continuosly updated process list, along with useful summary information

• the-poption allows to control a single process [agarfa]$ top -p 29696

top - 18:58:50 up 10:32, 7 users, load average: 0.18, 0.28, 0.27 Tasks: 1 total, 0 running, 1 sleeping, 0 stopped, 0 zombie

Cpu(s): 9.9%us, 1.8%sy, 0.2%ni, 87.2%id, 0.6%wa, 0.1%hi, 0.3%si, 0.0%st Mem: 2074216k total, 2018076k used, 56140k free, 54776k buffers

Swap: 3903784k total, 23580k used, 3880204k free, 1501260k cached PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND 29696 alberto 20 0 7692 3400 2808 S 0 0.2 0:03.36 xclock

kill

• ToCtrl-csequence terminates a running program.

The sequence sends a SIGINTor interrupt signal to the process.

• Thekillcommand sends a signal to a job or process.

Type man killto get a table of all available signals.

• TheSIGTSTPandSIGCONTsignals stop and resume a background job

[agarfa]$ xcalc &

[2] 6080

[agarfa]$ ps 6215

PID TTY STAT TIME COMMAND 6215 pts/6 S 0:00 xcalc

[agarfa$ kill -s SIGTSTP 6215

[2]+ Stopped xcalc

[agarfa]$ ps 6215

PID TTY STAT TIME COMMAND 6215 pts/6 T 0:00 xcalc

[agarfa]$ kill -s SIGCONT 6215 [agarfa]$ ps 6215

PID TTY STAT TIME COMMAND 6215 pts/6 S 0:00 xcalc

[agarfa]$ kill -s SIGINT 6215 [agarfa]$ ps 6215

PID TTY STAT TIME COMMAND [agarfa]$