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It seems like a trivial issue, but I did not find a solution.
I have a number of log files in a php installation on Debian/Linux that tend to grow quite a bit and I would like to trim nightly to the last 500 lines or so.
How do I do it, possibly in shell and applying a command to *log?
For this, I would suggest to use logrotate with a configuration to your liking instead of programming your own script.
There might be a more elegant way to do this programmatically, but it is possible to use tail and a for-loop for this:
for file in *.log; do
tail -500 "$file" > "$file.tmp"
mv -- "$file.tmp" "$file"
done
If you want to save history of older files, you should check out logrotate.
Otherwise, this can be done trivially with the command line:
LOGS="/var/log"
MAX_LINES=500
find "$LOGS" -type f -name '*.log' -print0 | while read -d '' file; do
tmp=$(mktemp)
tail -n $MAX_LINES $file > $tmp
mv $tmp $file
done
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I know what the commands ls and wc do, but I can not find out what ls > wc and ls | wc will show. Can someone please help me flush out the meaning of this commands?
ls | wc The output from the ls command is piped into the wc command. So it will count the words which are in the output of ls. So you see simply the number of files read by ls.
ls > wc This creates a new file in your current working directory with the name wc with the output of your ls command. The program wc is not used here, simply a new file with the same name is created. You can simply look into this new file with your favorite editor or simply use cat for it.
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My friend just passed me this command to count the number of files in a directory:
$ ls -lt | wc -l
Can someone please help me flush out the meaning of this command? I know that ls is to list all the files. But what does -lt mean?
Also, I get a different count if I use ls | wc -l with no -lt option. Why is that the case?
You'll want to get familiar with the "man (manual) pages":
$ man ls
In this case you'll see:
-l (The lowercase letter ``ell''.) List in long format. (See below.) If
the output is to a terminal, a total sum for all the file sizes is
output on a line before the long listing.
-t Sort by time modified (most recently modified first) before sorting the
operands by lexicographical order.
Another way you can see the effect of the options is to run ls without piping to the wc command. Compare
$ ls
with
$ ls -l
and
$ ls -lt
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To count the number of files in a directory, I typically use
ls directory | wc -l
But is there another command that doesn't use wc ?
this is one:
ls -l . | egrep -c '^-'
Note:
ls -1 | wc -l
Which means:
ls: list files in dir
-1: (that's a ONE) only one entry per line. Change it to -1a if you want hidden files too
|: pipe output onto...
wc: "wordcount"
-l: count lines.
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I have a large list of files that I want to rename.
Much like this
So this is what my files look like
something.pcap1
something.pcap10
something.pcap11
something.pcap12
...
something.pcap111
something.pcap1111
essentially I want to rename all of the files so that the numbers get padded with 0's and they are 5 digit numbers.
something.pcap00001
A simple for loop should do the trick (can be script file):
for file in $(ls -1 something.pcap*); do
[[ ${file} =~ ^something.pcap([[:digit:]]*).* ]]
newfile=$(printf "something.pcap%05d" ${BASH_REMATCH[1]})
mv ${file} ${newfile}
done
Something like this?
rename 's/\d+$/sprintf("%05d",$&)/e' soemthing.pcap*
Note: this works with the rename as found in debian and its derivates.
What about something like this?
#!/bin/bash
for i in $(ls something.pcap*); do
q=$(echo $i|sed -e 's/pcap/pcap00000/;s/pcap0*\([0-9]\{6,\}\)$/pcap\1/')
mv $i $q
done
I hope this will help
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I know that
cat file1 >> file2
would append the contents of file1 at the end of file2. On the other hand, how can I append the contents of file1 at the beginning of file 2, and not at its end?
Actually, i have a single master file M, and several other files in a directory D. I want to append the contents of file M at the beginning of all the files in the directory D.
Just do:
cat file1 file2 > tmp && mv tmp file2
For each file you could do:
cat MASTER file >> file.tmp
And then move file.tmp over file.
You will have to use a temporary file and rename it after merge.
Example:
echo -e "a\nb\nc" > LETTERS
echo -e "1\n2\n3" > NUMBERS
cat NUMBERS LETTERS > TMP
mv TMP LETTERS
cat LETTERS
Your command might look something like:
for file in $( find -name "*.java" ); do cat PREPEND ${file} > ${file}.tmp; mv ${file}.tmp ${file}; done