Guide to Unix/Commands/Miscellaneous
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[edit] sync
sync write memory buffers to disk
Example: Sync has no options, doesn't display any messages
$ sync
Tips:
It is always good to type sync a couple of times, one the important functions of sync is to update your superblock information.
The sync calls sync Unix system call and exits with success code '0' or '1' if it fails. These exit codes stored in $? variable.
$ sync $ echo $? 0
The above example shows that sync was successful.
[edit] echo
echo outputs its parameters to the standard output.
Examples:
$ echo "hello world" hello world
Tips: Some common echo usage:
Check a shell variable:
$ echo $EDITOR emacs
Check the parameters passed in the previous command:
$ ls -l ......... $ echo $_ -l
Check the current parent process:
$ echo $0 bash
Check the exit code of the last command:
$ echo $? 0
Create a empty file (same as touch /tmp/newfile):
$ echo "" > /tmp/newfile
Create a new file with some text:
$ echo "exec fluxbox" > ~/.xinitrc
Add (append) a new line to end of file:
$ echo "A New Line" >> /tmp/newfile
[edit] cal
cal displays a calender for the current month. If the command is followed by a date (a month or a year) it will return a calender for that period.
Examples:
$ cal
April 2004
Su Mo Tu We Th Fr Sa
1 2 3
4 5 6 7 8 9 10
11 12 13 14 15 16 17
18 19 20 21 22 23 24
25 26 27 28 29 30
$ cal 01 2007
January 2007
Su Mo Tu We Th Fr Sa
1 2 3 4 5 6
7 8 9 10 11 12 13
14 15 16 17 18 19 20
21 22 23 24 25 26 27
28 29 30 31
$ cal -3 Shows current, previous and next month (default on some implementations)
$ cal -3 04 2004 Shows April 2004, as well as the previous (March) and following (May) month
$ cal -1 Shows the current month (default on some implementations)
$ cal 2004 Shows a calendar for the whole year 2004
$ cal -j Shows this months calendar with day-of-year number (counted from January 1st) rather than the date
Tips: The Gregorian Calendar was adopted in the British Empire in 1752. The 2nd day of September 1752 was immediately followed by the 14th day of September, as shown by the example below.
$ cal 9 1752
September 1752
Su Mo Tu We Th Fr Sa
1 2 14 15 16
17 18 19 20 21 22 23
24 25 26 27 28 29 30
[edit] date
date displays the current date and time.
Example:
$ date Mon Jun 26 12:34:56 CDT 2006
[edit] time
time time a program
Example:
$ time gcc apache.c real 0m1.818s user 0m0.770s sys 0m0.210s
[edit] from
from display the names of those who sent you mail recently
Example:
$ from From andy@box.po Sat Feb 05 08:52:37 2005 From andy@box.po Sat Feb 05 08:53:52 2005
Count the number of mail in your mailbox
$ from -c There are 2 messages in your incoming mailbox.
[edit] mail
mail allows you to read and write emails.
Example:
$ mail No mail for user. $ mail user2 Subject: What's up? Hi user2, you can delete this rubbish by pressing 'd'. Cc: user
Tips: Note that you need to press enter then ctrl+d to confirm.
$ mail Mail version 8.1 6/6/93. Type ? for help. "/var/spool/mail/user": 1 message 1 new >N 1 user@unix.com Tue Jun 27 12:34 16/674 "What's up?" &
Tips: Press enter to read.
[edit] clear
clear clears the screen.
Example:
$
[edit] PS1
PS1 is an environment variable which defines the shell prompt. If not defined, the prompt defaults to "$"
Example:
$ PS1='yes? ' yes? PS1='$ ' $
A more complicated example:
$ PS1='*\u@\H* \t \d [\W]\n$ ' *user@unix.com* 12:34:56 Tue Jun 27 [home] $
