Shell Programming and Scripting

Hi, I'm writing a long script for bash (on RHEL 5.0) to execute many commands. So, my idea is to create a function to deal with error checking and logging (see ceckoutput() below). This works with all commands except for sed. I think it may be a problems with escaped characters. So I did the following tests :

bash-3.00$ bin/sed -i -e 's/\(.* \)/\1 console=ttyS0,115200/' grub.conf
bash-3.00$ echo $?
0
bash-3.00$ export cmnd="/bin/sed -i -e 's/\(.* \)/\1 console=ttyS0,115200/' grub.conf"
bash-3.00$ echo $cmnd
/bin/sed -i -e 's/\(.*\)/\1 console=ttyS0,115200/' grub.conf
bash-3.00$ $cmnd
/bin/sed: -e expression #1, char 1: unknown command: `''

I even tried changing the quotes to avoid shell substitutions:

export cmnd='/bin/sed -i -e "s%\(.*\)%\1 console=ttyS0,115200%" grub.conf'
bash-3.00$ $cmnd
/bin/sed: -e expression #1, char 1: unknown command: `"'

Any ideas why this is happening?
Would it be a good idea idea to use awk to edit the file ? if so please help me with that command.


ceckoutput (){

$1 2>&1 |tee -a $LOGFILE

if [ ${PIPESTATUS[0]} -ne 0 ];then
echo "Error in installation!! See $LOGFILE"
exit 1
fi
}

Regards,
MacL

This should work:

Code:

sed -i 's/$/\ console=ttyS0,115200/' grub.conf

Hi danmero,

Unfortunately I get the same error:

[root@performance ~]# sed -i 's/$/\ console=ttyS0,115200/' grub.conf
[root@performance ~]# echo $?
0
[root@performance ~]# export cmnd="sed -i 's/$/\ console=ttyS0,115200/' grub.conf"
[root@performance ~]# $cmnd
sed: -e expression #1, char 1: unknown command: `''

There is a problem when the sed command is stored in the env variable and then called. This is strange because it works with every other command I tried.

Why use a variable, which has all the disadvantages of an alias without any of its (few) advantages?

Why not just use the command itself?

If you are going to be executing it more than once and want to save typing (and don't know how to copy and paste), put it in a function:

Code:

cmnd()
{
   sed -i.bak -e 's/\(.* \)/\1 "$@"
}

Hi chfajohnson,

Actually I’m not using variables as they I posted. I did that to show what’s happening when I pass the command as a parameter to a function that executes it.
In fact, I don’t need to execute the same command many times. Actually there are many different commands. Since this will be an installation script executed by other people I need to log each output and check for errors. Instead of repeating that one every command I decided to have a function that will receive each command, execute it and perform the logging and error checking (something like ceckoutput (), see above ). Actually, it works for every command but sed.

Do you advice me a different way of doing this?