Useful Scripts

iDog

Find & Replace Strings

• Search for string in all files in a dir and all of its sub-dirs

grep [-l] string $(find dir [-name filename])

[NOTE] $() is the same as ``

• String substitution in files

perl -pi~~~ -e 's/oldstr/newstr/' $(find dir [-name filename])
rm -rf $(find dir -name *~~~)

Redirection

File descriptors are represented as numbers. Following are those for std*:

file	file descriptor
STDIN	0
STDOUT	1
STDERR	2

• redirect stdout to file1, stderr to file2

app > file1 2> file2

• redirect both stdout and stderr to file

app > file 2>&1

• throw away output of some command (very useful in tasks in cron)

app > /dev/null 2>&1

• redirection both stdout and stderr to file, and show them in console

app 2>&1 | tee file

File Operation

Use command 'exec' to open and close files by file descriptors:

$ echo "Hello, world!" > aaa.txt   # make a file aaa.txt by write something to it
$ exec 3 < aaa.txt                 # open file '3', input from aaa.txt
$ cat <&3                          # redirect STDIN to '3'
Hello, world!
$ exec 3<&-                        # close file '3'

$ exec 4 > bbb.txt                 # open file '4' to output to bbb.txt
$ cat aaa.txt > &4                 # redirect STDOUT to '4'
$ exec 4>&-                        # close file '4'

The file descriptor '3' is like a 'file handle' of file 'aaa.txt', opened for reading; while '4' is like a handle of file 'bbb.txt', opened for writing.

Network

• trace the route:

tracert <ip_addr_or_host_name>

• list open ports

netstat -an

• web site performance test: use "ab" of Apache. Example: Simulate 1000 requests; 20 concurrent requests.

ab -n 1000 -c 20 http://idogicat.dip.jp/index.html
ab -n 1000 -c 20 http://idogicat.dip.jp/cgi-bin/webcat/bin/view

• resolve Apache log: use "logresolve" of Apache.

Add Color to Bash

To make ls show file list with colors:

ls --color

to configure the color:

dircolors –p > colors
# edit file colors to customize it to one's interest...

dircolors colors > .colors

# .colors is a script for the current shell. you can also modify on it to make it support other shells

source .colors    # put in .bashrc

Running command periodically

This can be used to monitor something:

Watch –n <seconds> <command>

Eg:

Watch –n 5 uptime

Watch –n 3 ls –l bigLogFile.log

Merging files

Merge two files, only keep one copy of duplicated lines:

cat file1 file2 | sort | uniq

Only get lines existing in both files:

cat file1 file2 | sort | uniq -d

Only get lines existing in only one of two files:

cat file1 file2 | sort | uniq -u

[NOTE]: uniq command only works properly when the input is sorted.

redirect man/info to a file

man xxx | col -b > man.txt
info xxx -o info.txt -s

Extract files

unzip example.zip 
tar xvf example.tar 
tar xvfz example.tar.gz 
tar xvfz example.tgz 
tar xvfj example.tar.bz2 

Linux 'tree' command

alias tree='find . -print | sed -e "s;[^/]*/;|__;g;s;__|;   |;g" '

# iDog's version
alias tree='find . -print | sed -e "s;[^/]*/;+-- ;g;s;+-- +;|    +;g;s;+-- +;|   +;g;s;+-- |;|    |;g"'