You can find out how comparisons work in the man page of "test" ("man test").
The opening square bracket ("[") is in fact just an alias or link for "/usr/bin/test", to make shell code more readable:
and
is basically the same, the former is just "more natural" to read than the latter. "if" just takes the return code of the following command and "test" returns "0" when the comparison is true, otherwise it returns "1". The following would also work:
or
The first one would always execute the "then"-branch, the second one always the "else"-branch..
I am taking an intro to unix class and I can not figure out how to do part of the question. I am writing script to be exictued by a program in the tutoral.
Question:
Write every line containing the word ``delete'' produced by ``man mail'' into a file called ``delete''. Hint: What does using... (1 Reply)
I'm new to unix commands and am wondering how you could create a page with html tags in it. echo "<b>Test</b>" > test.html doesn't work because of the tags. How would I do this. (4 Replies)
i'm trying to make a script that prints the name of the script for any command line parameter, here is what i have, and get `]]' unexpected:
what am i doing wrong? (3 Replies)
Hello. I'm a complete newbie to C programming. I have a C program that wasn't written by me where I need to write some wrappers around it to automate and make it easier for a client to use. The problem is that the program accepts standard input to control the program... I'm hoping to find a simple... (6 Replies)
If given some output such as:
"I'm having a senior moment"
How do you print the last six characters to the screen?
I'm thinking with awk or sed but can't remember how. (1 Reply)
Hi Guys,
I've been learning UNIX for the past couple of days and I came across this exercise, I can't get my head around it, so I would be ever so grateful if I could receive some sort of help or direction with this.
Create a file with x amount of lines in it, the content of your choice. ... (3 Replies)
Hi,
We have all the user account in a home direcory where their mail is stored and retrieved by email clients. We do however have /var/spool/mail with all the user accounts in it as well Our sendmail.cf is configured to use /var/spool/mqueue as the queue so .what is /var/spool/mail being used... (3 Replies)
hi everybody;
trying to c unix programming and ive stucked with a problem:
simple program
filedr=open("tempfile",O_RDWR|O_TRUNC,0);
write(filedr,msg1,6);
int i;
i=read(filedr,msg3,4);
it returns 0 bytes read ... why?
well if i try to poll() before read , it doesnt indicate POLLHUP or... (4 Replies)
Cheers!
In /etc/syslog.conf, if an error type is not specified, is it logged anywhere (most preferable is it logged to /var/log/messages) or not?
To be more precise I am interested in error and critical level messages. At default these errors are not specified in syslog.conf, and I need to... (6 Replies)
Discussion started by: dr1zzt3r
6 Replies
LEARN ABOUT FREEBSD
ddb
DDB(8) BSD System Manager's Manual DDB(8)NAME
ddb -- configure DDB kernel debugger properties
SYNOPSIS
ddb capture [-M -core] [-N -system] print
ddb capture [-M -core] [-N -system] status
ddb script scriptname
ddb script scriptname=script
ddb scripts
ddb unscript scriptname
ddb pathname
DESCRIPTION
The ddb utility configures certain aspects of the ddb(4) kernel debugger from user space that are not configured at compile-time or easily
via sysctl(8) MIB entries.
To ease configuration, commands can be put in a file which is processed using ddb as shown in the last synopsis line. An absolute pathname
must be used. The file will be read line by line and applied as arguments to the ddb utility. Whitespace at the beginning of lines will be
ignored as will lines where the first non-whitespace character is '#'.
OUTPUT CAPTURE
The ddb utility can be used to extract the contents of the ddb(4) output capture buffer of the current live kernel, or from the crash dump of
a kernel on disk. The following debugger commands are available from the command line:
capture [-M core] [-N system] print
Print the current contents of the ddb(4) output capture buffer.
capture [-M core] [-N system] status
Print the current status of the ddb(4) output capture buffer.
SCRIPTING
The ddb utility can be used to configure aspects of ddb(4) scripting from user space; scripting support is described in more detail in
ddb(4). Each of the debugger commands is available from the command line:
script scriptname
Print the script named scriptname.
script scriptname=script
Define a script named scriptname. As many scripts contain characters interpreted in special ways by the shell, it is advisable to
enclose script in quotes.
scripts
List currently defined scripts.
unscript scriptname
Delete the script named scriptname.
EXIT STATUS
The ddb utility exits 0 on success, and >0 if an error occurs.
EXAMPLES
The following example defines a script that will execute when the kernel debugger is entered as a result of a break signal:
ddb script kdb.enter.break="show pcpu; bt"
The following example will delete the script:
ddb unscript kdb.enter.break
For further examples, see the ddb(4) and textdump(4) manual pages.
SEE ALSO ddb(4), textdump(4), sysctl(8)HISTORY
The ddb utility first appeared in FreeBSD 7.1.
AUTHORS
Robert N M Watson
BUGS
Ideally, ddb would not exist, as all pertinent aspects of ddb(4) could be configured directly via sysctl(8).
BSD December 24, 2008 BSD