SysAdmin Tips

Renaming multiple files

for i in *.avi; do j=`echo $i | sed 's/find/replace/g'`; mv "$i" "$j"; done

for i in *.phtml; do mv $i ${i%.phtml}.php; done

Deleting files matching a pattern

find opt/Products -name "*.pyc" -exec rm '{}' \;

Sed: Stream Editor

Search/Replace:

sed 's/old/new/g' input.txt > output.txt

Faster:

sed '/old/ s/old/new/g' input.txt > output.txt

Do on a folder full of files:

#! /bin/sh
# Source files are saved as "filename.txt.bak" in case of error
# The '&&' after cp is an additional safety feature
for file in *.txt
do
cp $file $file.bak &&
sed 's/foo/bar/g' $file.bak >$file
done

Insert paragraph:

• e.g. search for lines `#include <termios.h>' and then write:

  #ifdef SYSV
  #include <termios.h>
  #else
  #include <sgtty.h>
  #endif
  

Now, for writing the same script on one line, the -e mechanism is needed... what follows each -e can be considered as an input line from a sed script file, so nothing kept us from doing:

sed -e '/#include <termios\.h>/{' \
-e 'i\' \
-e '#ifdef SYSV' \
-e 'a\' \
-e '#else\' \
-e '#include <sgtty.h>\' \
-e '#endif' \
-e '}'

1-liners:

• ​http://sed.sourceforge.net/sed1line.txt

Tutorial:

• ​http://sed.sourceforge.net/grabbag/tutorials/do_it_with_sed.txt

Collected resources:

• ​http://sed.sf.net/

Adding a swapfile

If you have a live system which you need to give extra swapspace too without a reboot, then can add a swapfile.

Note that a swapfile is much slower than a swap partition, which is -of course- slower than memory. The reason for this is to save the ship when the boat's going down, not increase preformance.

Create file:

dd if=/dev/zero of=/swapfile count=[size of swap, in 512B blocks]

Format it:

mkswap /swapfile -p 16384

Tell the kernel to use it at an lower priority (i.e. only use when swap parition is full):

swapon -p 16384 /swapfile 

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