Using the 'watch' command
Here's a useful command to keep an eye on what's going on with sendmail. You can see all the current sendmail connections, followed by the last 10 lines of the sendmail log, updated every second.
If you have a lot of sendmail connections, it will scroll off your screen and probably not be so useful. But on my moderate traffic server, with 10-15 connections at all times, it's just right.
watch -n 1 'ps afx --width=300|grep sendmail; \
echo;echo;tail -10 /var/log/maillog'
The \ is just for display purposes. You can put the whole
command on one line if you want to.
Using 'for loops' and 'seq' to handle files
To repeat a command or series of commands in the shell, you can use a for
loop, just like you would in most any progamming language. And the seq
command will generate a sequence of numbers for you. This makes processing image files,
for example, fairly simple.
Let's say you have files named "image001.jpg" through "image275.jpg" that you want
to run through some sort of image alteration program, img_foo. But img_foo
isn't smart enough to handle multiple files; it can only handle a single filename as
a runtime option. To process every file, you can do
for f in `seq -w 1 275`; do img_foo image$f.jpg; done
The -w switch for seq will pad the digits generated (1 to 275)
with leading zeros to keep all numbers the same width. The loop variable $f
gets assigned each seq-generated number in turn, so each pass through the loop gives a new
filename being passed to img_foo.
Try using seq alone, with and without the -w switch, to see
what it does. And remember, man is your friend -- man seq will
give you all the info you need.
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Bruce Timberlake
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