grep, cat, more, head, tail

grep

Purpose

Search for pattern & return lines matching the pattern

Examples

grep [your last name] /etc/passwd

grep network /etc

• Produces error: "grep: /etc: Is a directory"
• Why doesn't this work?

grep network /etc/*.conf

• Why does this one work?

grep network /*

• What am I trying to do?
• Produces error: "grep: /bin: Is a directory"
• Why doesn't this work? Notice also that it only looked at the immediate contents of /. It didn't go into any of those directories. Why not? What option should I have used?

grep -r network /*

• What does "-r" do?

cat

Purpose

Concatenate files & print results on the standard output

Examples

cat /etc/passwd

cat /etc/inittab

• Notice how the contents of the file zooms past

cat /etc/passwd /etc/inittab

• Note that you are NOT messing with the original files â•„ you're just concatenating them both & displaying the results to the screen

more

Purpose

Page through text one screenful at a time

Examples

more /etc/inittab

• spacebar = advance another screen
• b = back one screen
• q = quit

head

Purpose

Output the first part of files

Examples

head /etc/inittab

head -20 /etc/inittab

tail

Purpose

Output the last part of files. Especially useful for log files, which append newest entries at end of file.

Examples

tail /etc/inittab

tail -20 /etc/inittab

;, |, >, <

; (command terminator)

Purpose

Terminates commands so that several can be run in sequence

Examples

cd; ls -F

| (pipe symbol)

Purpose

Conduit between commands in which output from first command becomes input for second command

Examples

ls /dev | grep hda

ps -aux | grep root

> (greater than symbol)

Purpose

Redirect stdout from monitor to a file

Examples

ls -F /etc > /tmp/etc.txt

cat /etc/passwd /etc/inittab > /tmp/longfile.txt

ps aux | grep root > /tmp/psroot.txt

< (lesser than symbol)

Purpose

Redirect stdin from keyboard to a file, so that a command gets input from file instead of keyboard

Examples

sort < /etc/passwd

sort < /etc/passwd > /tmp/passwd.txt

The Wildcards: *, ?, [ ]

* (asterisk)

Purpose

Match zero or more characters in a filename

Examples

ls *

ls /etc/*.conf

cp /etc/* /tmp/etc

? (question mark)

Purpose

Match any single character in a filename

Examples

ls /etc/rc?.d

cp photo?.jpg /mnt/floppy

[ ] (square brackets)

Purpose

Match any single character between brackets in a filename

Examples

ls rc[1-3].d

history

history

Purpose

Show list of all commands entered on the command line

Examples

history

history 10

!10

!! = repeat last command

↑ [up arrow] = back through history

alias, unalias

alias

Purpose

Alternative name for a longer command

Examples

alias = display list of current aliases

alias la='ls -aF' ; alias

• Then try this: "la > /tmp/ls.txt"

alias md='mkdir'

• Redefine current commands so they have less to type

alias rm='rm -i'

• If you're paranoid & want to be reminded every time ...

unalias

Purpose

Remove alias

Examples

unalias la ; alias

&, ps, kill

& (ampersand)

Purpose

Run processes in the background, so they don't take control of your terminal (& have to be killed with ctrl+c)

Examples

nessus

• See how my terminal is "locked" by Nessus?

nessus &

• My terminal is unlocked and free for other commands. The number in backets is the process ID number for nessus.

locate network > network.txt &

ps

Purpose

Display list of running processes

Examples

ps = list all processes running at that moment

ps -x = list all process owned by you

ps -ax = list all process running on the machine

ps -aux = list all processes running on the machine & identify owner

• Note that init is always process 1; hence it is the "mother of all processes"

ps -aux --cols 125 = list all processes running on the machine & identify owner & print results to screen 125 characters wide

ps -aux | grep root

kill

Purpose

End running process

Examples

mozilla ; ps -aux ; kill [mozillaPID]

kill -9 PID = die now!

killev = kill all Evolution processes

date, cal

date

Purpose

Print curent date & time

Examples

date

rdate -p -s ntp.dgf.uchile.cl = connect to remote NTP server & set system time

cal

Purpose

Display calendar

Examples

cal

cal 1 2002

cal 1 02

cal 9 1752

cal 2002

wc, sort, split

wc

Purpose

Display line, word, & character count of text file

Examples

cd tmp ; ln -s /usr/share/doc/HTML/en/common/gpl-license gpl

wc gpl

wc -l gpl = number of lines

wc -w gpl = number of words

wc -c gpl = number of characters

sort

Purpose

Sort lines in a text file to stdout

Examples

sort /etc/passwd

sort /etc/passwd > /tmp/passwd.txt

split

Purpose

Split large file into smaller files

Examples

cd tmp

split -100 gpl splitgpl.

cat splitgpl.?? > gpl

df, du

df

Purpose

Display amount of disk space available on the filesystem

Examples

df

df -h = human-readable (K, M, G)

du

Purpose

Summarize disk usage for a file, or recursively for directories

Examples

cd /tmp ; du

du /etc

du -c /etc = print total

du -ch /etc = human-readable