Linux Format forums

[snuffsaid]

evening all,

I have been trying to get a shell script working that will automatically edit a text file. The text file is set out using ':' as a delimiter between bits of info, a bit like the /etc/passwd file. I am trying to use only bash shell scripting for this, no PHP, Ruby, PERL, etc. for reasons of portability, not all the machines have such goodies.
I have managed to get the script to edit a line by using the output of sed and redirecting it to a new file, then copying the file back over the original. Though this seems to leave a blank line in place of the old line if I remove the files entry with the script, though editing the second field does work.
Does anyone know of a more elegant way of doing this? If not with sed then I think all of my machines do have awk if that is of any help to someone.

Cheers

Pete

[Nigel]

What exactly are you trying to do to the file ? There's a good chance that both sed and awk can do what you want, but one may be easier than the other for the task you have in mind.

[nelz]

If using sed, the s command only replaces content within a line, you need d to delete a complete line or block of lines.

Also, use the -i option to modify a file in place instead of sending pout put to a temporary file, deleting and renaming.

As Nigel says, a clearer idea of what you are doing will result in a clearer recommendation.
_________________
Unix is user-friendly. It's just very selective about who it's friends are.

[snuffsaid]

Sorry for not providing more info, I didn't want to waffle on too much. I have a thrid party application that limits the amount of logins using the application, but does not limit the number of times a user can log in. I have found a way of limiting the users to be only able to login a certain number of times by editing the apps startup script to refer to another file to see how many times that user is allowed to log in. Now I am trying to create a script that can be run from the command line so the person in charge doesn't have to use vi. All he would need to do is <command> -a (add), -r (remove) -m(modify) and so on. This would edit the file, whichis only about 20 lines long and is set out like "username:number of logins". The : can be replaced by anything really.
Hope I haven't waffled on too much and it's made things a little clearer
In the mean time I'll go and try the -i option
Many Thanks

Pete

[jjmac]

Information isn't waffle .

Sounds like a job for "sed" though. A google on sed will come up with lots of diverse sources of information. Including histories, "examples" etc. Unfortuately the man page is quite lacking. I think that because sed has been around for such a long time, it isn't really centralised to the dgree where a single site will provide all the required documentation. So, as a result, it is scattered. Certainly, imo, one of the great unix tools.


jm

[nelz]

The sed manpage is limited, but the last paragraph tells you all you need to know, full documentation is in the info page.

You can do what you want with

[jjmac]

, wish i had looked at the info page at the time (good_grief.png)
_________________
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The FVWM wm -=- www.fvwm.org -=-

Somebody stole my air guitar, It happened just the other day,
But it's ok, 'cause i've got a spare ...

[alloydog]

[snuffsaid]

a big thank you to you all. I was staring at the man page and even the "classic shell scripting" book late at night but just could not see for looking, as they say.

Cheers

Pete

[jjmac]

alloydog wrote:

>>
You mean:
>>

In a nut shell (hehehe) (um ,,, that is a jpg you know ! )


snuffsaid:
>>
I was staring at the man page and even the "classic shell scripting" book late at night but just could not see for looking,
>>

Tell me about it (grin), mind you, some of the google feed back on sed is worth the squize

jm
_________________
http://counter.li.org
#313537

The FVWM wm -=- www.fvwm.org -=-

Somebody stole my air guitar, It happened just the other day,
But it's ok, 'cause i've got a spare ...