Guys any tips on printing a certain error message to stderr and exiting should a command fail within a ksh script? I'm trying to null some output files.
Touch isn't suitable as i need to null them.
print "" > file isn't suitable as i need to check elsehere for if they are 0bytes or not.
I've tried these below examples and none work correctly. I don't want to have to put a check after each command as :-
Code:
if [[ $? -ne 0 ]];then
print "error blah blah" >&2
exit 2
fi
Below tests don't work correctly. I'm guessing its spawning something.
Seems i was almost there but didn't use the correct { }
Could you explain the difference between { } and ( ) in the command grouping? Also i notied the ; at the end before } is vitally important otherwise the next command doesn't work.
e.g
Code:
This works and exits if cant null but echos got to here if can.
> ${OUTFILE} || { print "ERROR: cannot null output file. Exiting\n" >&2; exit 2; }
> ${TMPFILE} || { print "ERROR: cannot null tmp file. Exiting\n" >&2; exit 2; }
echo "got to here"
This doesnt work and never gets to echo even if null is successful
> ${OUTFILE} || { print "ERROR: cannot null output file. Exiting\n" >&2; exit 2 }
> ${TMPFILE} || { print "ERROR: cannot null tmp file. Exiting\n" >&2; exit 2 }
echo "got to here"
() executes the statements in a new subshell, with separate state. {} executes stuff in the current shell.
Example:
Code:
(aVariable="hello"); echo $aVariable
this doesn't print "hello" because the variable was assigned inside a new shell, whose state was discarded when the () expression ended. Think of variable scoping in C; variables live and die inside the block where they're declared.
Code:
{aVariable="hello"; }; echo $aVariable
this prints "hello" because the variable was assigned in the same shell as the next statement.
It's the same difference as:
Code:
sh myScript.sh
and
Code:
source myScript.sh
Also, yes, you need a semicolon to end the last statement inside {}; that's how the shell's grammar is defined.
Kind of how you can either do this:
Code:
if $condition; then $statements; fi
or this, using newlines instead of semicolons to separate the syntax parts:
Code:
if $condition
then
$statements
fi
According to the bash man page, it's different from () because { and } are reserved words instead of metacharacters, which means they don't automatically cause word breaks. Presumably the same applies in the rest of the shells.
Last edited by EagleFlyFree; 04-23-2009 at 03:14 PM..
Dude thats real great and an informative reply. Thanks a lot. Its certainly giving me a better understanding of the shell rather than just trying things until they work
Don't mention it; I love yapping about bash.
Its man page is long and daunting, but flick through it every once in a while; you're bound to learn great tidbits every time.
The parts about history and readline are particularly cool, and they're handy and fun to use.
Hi,
i am new here let me say HI for all.
now i have a question please:
i am sending one command to my machine to create 3 names.
if one of the names exists then the box return error message that already have the name but will continue to create the rests.
How i can break the command and... (7 Replies)
Input is list of Server's, script is basically to remove old_rootvg, So it should check first command "alt_rootvg_op -X old_rootvg" if it passes move to next server and starts check and if it fails moves to other command "exportvg old_rootvg" for only that particular server. I came up with below,... (6 Replies)
I am working with a sh script on a solaris 9 zone (sol 10 host) that grabs information to build the configuration command line. the variables Build64, SSLopt, CONFIGopt, and CC are populated in the script. the script includes
CC=`which gcc`
CONFIGopt=' --prefix=/ --exec-prefix=/usr... (8 Replies)
Hi,
Want to log the output of command & check the exit status to find whether it succeeded or failed.
> ls abc
ls: abc: No such file or directory
> echo $?
1
> ls abc 2>&1 | tee log
ls: abc: No such file or directory
> echo $?
0
Tee commands changes my exit status to be always... (7 Replies)
Hi everyone,
when executing this command in unix:
echo "WM7 Fatal Alerts:", $(cat query1.txt) > a.csvIt works fine, but running this command in a shell script gives an error saying that there's a syntax error.
here is content of my script:
tdbsrvr$ vi hc.sh
"hc.sh" 22 lines, 509... (4 Replies)
hi All
I have a scritp running which connects to a local host and then gets a value from a field and then ftp that value to antoher server. It is running fine, and from crontab it gives the output to a file, the problem is sometime it doesnt run but if i check the output file it does not show one... (0 Replies)
I want to capture actual error message in case the commands I use in my shell script fails.
For eg:
ls -l abc.txt 2>>errorlog.txt
In this case I understand the error message is written to the errorlog.txt and I assume its bacause the return code from the command ls -l abc might return 2 if... (3 Replies)
I need to print some mandatory instructions if something fails in the script. I am using set -e to check and exit the script if some scripts/commands return non zero exit code. Is there any way to print these instructions with set command?? (0 Replies)
04-24-2009
