Command line Perl for sysadmins

Replies are listed 'Best First'.
Re: Command line Perl for sysadmins by davidrw (Prior) on Mar 24, 2006 at 14:44 UTC
Goo article .. I had few comments though (might be biased from a perl guy side instead of a sysadmin side ;) ): There's no reference material mentioned -- I think it would be extremely useful to have mentioned "man perlrun" and "man perlre" as "For more information" or "Advanced Reading" or something. e.g. `-l` and `-0` are both quite useful too (not saying they should be in the article, but somewhere where an interested party can discover them). Also `perl -pe 's/foo/bar/'` is given a lot of focus, which is why I think perlre should be mentioned. `perl -pe '' foo.txt` vs `perl -pe '' < foo.txt` -- both are used .. IMHO I think it's simpler to just stick to the first one since that one supports taking multiple filenames .. one might be confused by the difference when there really isn't one. `find . \| xargs perl -p -i.old -e 's/oldstring/newstring/g'` I didn't like this example because the `find .` will spit out directory names which will cause warnings from perl .. Especially in sysadmin context, should be `find . -type f` perl -e 'for("B","C","D"){`scp command.pl $_:`; `ssh $_ command.pl`; }' Didn't like this example (though admittedly don't have a better one) cause it's trivial (and arguably better) to write in bash: `for h in B C D ; do scp command.pl $h; ssh $h command.pl ; done` One last note, of an additional technique I personally find useful -- just use perl to generate the shell commands, much like xargs. For example: # perl -e 'for(<access_log.>){$a = $_; s/log/log.old/; `cp $a $_`}' ls access_log. \| perl -pe 'chomp; $f0 = $_; s/log/log.old/; $_="cp $f +0 $_\n"' # note: don't use $a # other ways to write it: # \| perl -lne 'chomp; print "cp $_ $_.old"' # \| perl -pe 's/.+/cp $& $&.old/' [download] Now, that can be previewed to make sure it's right, and then either redirected into a file and run as a shell script (which has the advantage of doubling as a log of what was done), or the output can be copy/pasted into the shell or piped to bash. I also use this approach often to generate SQL commands ... e.g. take a data file and create INSERT or UPDATE statements.	[reply] [d/l] [select]

Replies are listed 'Best First'.

Re: Command line Perl for sysadmins
by davidrw (Prior) on Mar 24, 2006 at 14:44 UTC

There's no reference material mentioned -- I think it would be extremely useful to have mentioned "man perlrun" and "man perlre" as "For more information" or "Advanced Reading" or something. e.g. -l and -0 are both quite useful too (not saying they should be in the article, but somewhere where an interested party can discover them). Also perl -pe 's/foo/bar/' is given a lot of focus, which is why I think perlre should be mentioned.
perl -pe '' foo.txt vs perl -pe '' < foo.txt -- both are used .. IMHO I think it's simpler to just stick to the first one since that one supports taking multiple filenames .. one might be confused by the difference when there really isn't one.
find . | xargs perl -p -i.old -e 's/oldstring/newstring/g' I didn't like this example because the find . will spit out directory names which will cause warnings from perl .. Especially in sysadmin context, should be find . -type f
perl -e 'for("B","C","D"){`scp command.pl $_:`; `ssh $_ command.pl`; }' Didn't like this example (though admittedly don't have a better one) cause it's trivial (and arguably better) to write in bash: for h in B C D ; do scp command.pl $h; ssh $h command.pl ; done

#  perl -e 'for(<access_log.*>){$a = $_; s/log/log.old/; `cp $a $_`}'
ls access_log.* | perl -pe 'chomp; $f0 = $_; s/log/log.old/; $_="cp $f
+0 $_\n"'
 # note: don't use $a
  # other ways to write it:
    # | perl -lne 'chomp; print "cp $_ $_.old"'
    # | perl -pe 's/.+/cp $& $&.old/'
[download]

[reply]
[d/l]
[select]