Twitter
Email
RSSChang the swap behavior of linux
The default swappiness is 60. It can be 0-100, with the bigger value more pages will be swapped to harddisk from memory.
If you want to use more physical memory and less swap, decrease the number.
echo 40 > /proc/sys/vm/swappiness
What you may not know about linux sed
1. Separator can be any symbol.
This also works:
echo '/etc/python3/dummy' | sed 's|/etc/python3/|/etc/python2/|'
output:
/etc/python2/dummy
In this example above I used | to replace the normally used separator /
Two ways to write literal strings containing line breaks to a file
1. Use printf
printf "line 1 line2 line 3 containing a variable: ${PWD} line 4 contains a quote mark ' and \" ">temp.txt cat temp.txt
Notice double quote ” needs to be escaped.
2. Use Here Doc:
cat > temp.txt <<EOF line 1 line2 line 3 containing a variable: ${PWD} line 4 contains a quote mark ' and " EOF cat temp.txt
Notice double quote ” doesn’t need to be escaped.
Also notice “EOF” can actually be anything. This also works
cat > temp.txt <<SEPARATOR line 1 line2 line 3 containing a variable: ${PWD} line 4 contains a quote mark ' and " SEPARATOR cat temp.txt
Notice double quote ” doesn’t need to be escaped.
http://en.wikipedia.org/wiki/Here_document#Unix-Shells
split string in Bash
emails="email1@gmail.com;email2@gmail.com;email3@gmail.com" emails=${emails//;/ } #replace ; with space arr_emails=($emails) # put them into an array for item in ${arr_emails[@]}; do echo $item done
In fact this works also. You don’t really need arrays
emails="email1@gmail.com;email2@gmail.com;email3@gmail.com" emails=${emails//;/ } #replace ; with space for item in $emails; do echo $item done
But with using arrays, you can do many other operations http://www.thegeekstuff.com/2010/06/bash-array-tutorial/
For the bash or sh version that “emails=${emails//;/ } ” doesn’t work, use tr command:
emails="email1@gmail.com;email2@gmail.com;email3@gmail.com" emails=$(echo $emails | tr ";" " ") for item in $emails; do echo $item done
This also works:
emails="email1@gmail.com;email2@gmail.com;email3@gmail.com" emails=$(echo $emails | tr ";" "\n") for item in $emails; do echo $item done
sed regular expressions
echo 'iweigh297lbs' | sed 's/.*[^0-9]\([0-9]\+\).*/\1/'
The expression has to match the whole line.
Greed: The expression will match the largest possible from left to right.
This won’t work.
echo 'iweigh297lbs' | sed 's/.*\([0-9]\+\).*/\1/'
Output 7
This won’t work
echo 'iweigh297lbs' | sed 's/.*[^0-9]\([0-9]*\).*/\1/'
This works
echo 'iweigh297lbs' | sed 's/.*[^0-9]\([0-9][0-9]*\).*/\1/'
+ has to be escaped. * should not be escaped.