xargs - how to run only when something is found? 1

[stfaprc]

the following line works fine:
ls -l | grep " 7" | cut -c 57-70 | xargs rm

except, I don't want the 'rm' to run if the grep come up empty. How do I write this so it only runs if the grep finds?

 

[PHV]

you may try this:

ls -l | awk '{/       7/{system("rm "substr($0,57,14))}'

Hope This Helps, PH.
FAQ219-2884
FAQ181-2886

 

[stfaprc]

Where is the first closing curly bracket supposed to be?
I put it after the 7/ , and the line operated on every file and not just those 7 bytes large.

 

[Annihilannic]

If you don't want to run rm just because of the Usage: rm [-Rfir] file ... message you get when it has no arguments, try using rm -f instead, because that never complain.

The other option is xargs -L n rm, which will only run the command if there is at least one argument being supplied. You will need to take a guess at a suitable value of n though, say 100?

Annihilannic.

 

[PHV]

OOps, sorry for the typo:
ls -l | awk '/ 7/{system("rm "substr($0,57,14))}'

Hope This Helps, PH.
FAQ219-2884
FAQ181-2886

 

[stfaprc]

The other option is xargs -L n rm, which will only run the command if there is at least one argument being supplied. You will need to take a guess at a suitable value of n though, say 100?

Annihilannic.

the man page does not mention that feature of -l .
Does this mean that 'xargs' actually causes one run of command, as opposed to the "awk" method which would run an individual instance of the command on each hit?

 

[Annihilannic]

Unfortunately the xargs options seem to vary quite a lot on different operating systems; what OS are you using?

-L will do the trick on HP-UX or AIX. -r is the one you want on GNU/Linux systems.

Annihilannic.

 

[stfaprc]

sorry, mislead you.
running RH9 and it does list -l along with --max-lines.
What it does not say is that if there are NO lines then the xargs will not run at all.

 

[zaxxon]

Annihilannic said -r on Linux. Your RH is a Linux, so...

--no-run-if-empty, -r
              If the standard input does not contain any nonblanks, do not run the command.
              Normally, the command is run once even if there is no input.  This option is a GNU extension.

This is from a Debian box, should look similar in your man page.

laters
zaxxon

 

[stfaprc]

ohh, the -r is what is preventing the running. thanks.