For Loop Question 2

[Dagon]

This has probably been asked before, but searching for the word "for" is not the easiest thing...

I have a simple for loop such as:

for x in *.log
do
echo $x
done

This works fine except in the situation where there are no log file, in which case it returns the input criterion ("*.log"). I've got round it in the past by putting in a line to exit the loop if what I get back the same string that I was searching for, but I can't help thinking there must be a better way.

 

[PHV]

for x in `ls *.log 2>/dev/null`

Hope This Helps, PH.
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[SamBones]

Or...

ls -1 *.log | while read X
do
   echo ${X}
done

This will do the loop zero times of there is no file to match the pattern.

Hope this helps.

 

[PHV]

This will do the loop zero times
But you get an error message ...

 

[azimuth0]

A sexier version that works better with excessively large numbers of files:

find . -name '*.log' -exec echo {} \;

: Daniel :

-

http://www.bitmuse.com/

 

[p5wizard]

Yes Daniel, but if it's just echoing of names, no need to "exec echo", that is kind of costly. The following does exactly the same.

find . -name '*.log' -print

I would also expect Dagon to want to use the names further on in the script so with a "while read":

find . -name '*.log' -print|while read X
do
...
whatever ${X}
...
done

or PHV's "for" method:

for X in `find . -name '*.log' -print`
do
...
whatever ${X}
...
done

HTH,

p5wizard

 

[stefanwagner]

Yes p5wizard, but if it's just printing of names, no need to "-print". The following does exactly the same.

find . -name '*.log'

(at least my gnu:find on linux).

seeking a job as java-programmer in Berlin:

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[PHV]

at least my gnu:find on linux
Any posix compliant find should have the default operation set to -print unless the -none operation is involved.

Hope This Helps, PH.
Want to get great answers to your Tek-Tips questions? Have a look at FAQ219-2884 or FAQ181-2886

 

[p5wizard]

I agree about the default action "-print", but it doesn't harm if "-print" is specified in a shell script. It just makes the script behave even if "find" doesn't.


HTH,

p5wizard

 

[azimuth0]

It seemed reasonable that the 'echo' bit was just a placeholder for what he really wanted to do with the files.

: Daniel :

-

http://www.bitmuse.com/

 

[stefanwagner]

you're right, azmuth0.


seeking a job as java-programmer in Berlin:

http://home.arcor.de/hirnstrom/bewerbung

 

[p5wizard]

Not if in a script you need to use the found filename more than once. You would need a 'find' script and a separate 'execute' script to use in the '-exec' option... I like to keep my scripts self-contained.

consider this simple example:

find ...|while read name
do
grep "ERROR" $name >>all_errors
grep "WARNING" $name >>all_warnings
mv $name archdir
done

HTH,

p5wizard