02-21-2010
In general:
- Call as few things as possible. If you have a loop, watch the calls you make in it. A Useless Use Of Cat that happens 10,000 times isn't a trivial waste anymore. Often people call sed, awk, etc. for single strings, which can be a waste -- you might be able to refactor that, running sed once on a big chunk of data then reading the result into the shell piecewise instead of running sed 10,000 times. Or better yet, instead of making an external call for that:
- Rely more on shell builtin functions. You can often use the shel builtin read and the IFS variable that controls it to replace things that call cut thousands of times, use shell expressions instead of a regex in sed, and so forth.
- Limit the number of pipes. Each pipe represents another process that's either competing with you for CPU time, making your shell wait while it reads input, or making your shell wait before you can read its output. I wrote a homemade linewrapper in BASH that used at least six subshells feeding data into each other, that ended up processing text files at about 10 kilobytes per second.
- Are there existing tools that can do what you want? A while ago there was a thread where someone needed to translate a giant single-line flat file. I wrote a solution in BASH that was horribly slow, then realized the file was so consistent I could just use dd with a few unusual options to convert it in no time flat.
10 More Discussions You Might Find Interesting
1. Filesystems, Disks and Memory
Hello,
I have a Supermicro server with a P4SCI mother board running Debian Sarge 3.1. This is the "dmidecode" output related to RAM info:
RAM speed information is incomplete.. "Current Speed: Unknown", is there anyway/soft to get the speed of installed RAM modules? thanks!!
Regards :)... (0 Replies)
Discussion started by: Santi
0 Replies
2. Shell Programming and Scripting
hi i have a script that is taking the difference of multiple columns in a file from a value from a single row..so far i have a loop to do that.. all the data is floating point..fin has the difference between array1 and array2..array1 has 700 x 300= 210000 values and array2 has 700 values..
... (11 Replies)
Discussion started by: npatwardhan
11 Replies
3. Shell Programming and Scripting
Hey together,
You should know, that I'am relatively new to shell scripting, so my solution is probably a little awkward.
Here is the script:
#!/bin/bash
live_dir=/var/lib/pokerhands/live
for limit in `find $live_dir/ -type d | sed -e s#$live_dir/##`; do
cat $live_dir/$limit/*... (19 Replies)
Discussion started by: lorus
19 Replies
4. Shell Programming and Scripting
I have a script that processes a fair amount of data -- say, 25-50 megs per run. I'd like ideas on speeding it up. The code is actually just a preprocessor -- I'm using another language to do the heavy lifting. But as it happens, the preprocessing takes much more time than the final processing... (3 Replies)
Discussion started by: CRGreathouse
3 Replies
5. Filesystems, Disks and Memory
I analysed disk performance with blktrace and get some data:
read:
8,3 4 2141 2.882115217 3342 Q R 195732187 + 32
8,3 4 2142 2.882116411 3342 G R 195732187 + 32
8,3 4 2144 2.882117647 3342 I R 195732187 + 32
8,3 4 2145 ... (1 Reply)
Discussion started by: W.C.C
1 Replies
6. Shell Programming and Scripting
I had written a perl script to compare two files: new and master and get the output of the first file i.e. the first file: words that are not in the master file
STRUCTURE OF THE TWO FILES
The first file is a series of names
ramesh
sushil
jonga
sudesh
lugdi
whereas the second file (could be... (4 Replies)
Discussion started by: gimley
4 Replies
7. Shell Programming and Scripting
Hi,
Im quite new to scripting and would like a bit of assistance with trying to speed up the following script. At the moment it is quite slow....
Any way to improve it?
total=111120
while
do
total=`expr $total + 1`
INCREMENT=$total
firstline = "blablabla"
secondline = "blablabla"... (5 Replies)
Discussion started by: brunlea
5 Replies
8. Shell Programming and Scripting
hey guys i have a perl script wich use to compare hashes but it tookes a long time to do that so i wich i will have the soulition to do it soo fast
he is the code
<redacted> (1 Reply)
Discussion started by: benga
1 Replies
9. Shell Programming and Scripting
Hi
I have written a shell script which will test 300 to 500 IPs to find which are pinging and which are not pinging.
the script which give output as
10.x.x.x is pining
10.x.x.x. is not pining
-
-
-
10.x.x.x is pining
like above.
But, this script is taking... (6 Replies)
Discussion started by: kumar85shiv
6 Replies
10. Shell Programming and Scripting
Hello,
I am basic level shell script developer. I have developed the following script. The shell script basically tracking various files containing certain strings. I am finding options to make the script run more faster. Any help/suggestion would be appreciated :)
#! /bin/bash
# Greps for... (6 Replies)
Discussion started by: Bhanuprasad
6 Replies