Useful Linux Commands

Linux offers very powerful tools for text processing, files search, etc.

This is a short overview of some commands that we are using regularly

Help and description of Linux commands

for many commands to get more info about options and how to use, you can type in terminal

$ commandname --help

$ man commandname

Connecting

Connect to another machine

$ ssh user@host

$ mysql -uuser -p -hhost

MySQL

See also: Using My SQL

Create a database

create database dbname

Set permissions

grant all on dbname.* to "user"@"192.168.1.%" identified by "password";

grant all on dbname.* to "user"@"localhost" identified by "password";

Load from file into database

$ mysql -uuser -p databasename<filename

Dump data from database into file

$mysqldump -uuser -p -hhost dbname > filename.mysql

Set cache variable

mysql> set global query_cache_size = 1000000;

mysql> show global variables like 'query_cache_size';

Searching

To search for files or folders

• find -name
• locate
• wheries
• which

To search for active java processes

e.g. to test whether Pentaho server is running

$ ps -ef |grep java

Text processing

See also: Reading text files

To open text documents in terminal

• vi
• less
• tail
• tail -f
• head

• :q to exit
• / to search for a string

To search for a string in multiple text files

$ grep 'string' *.txt

To search recursively for all files containing the word 'string'

$ grep -r -o 'string' *

• -o only show file names, suppress content
• -r recursive

Replace strings in multiple files

$ sed -i 's/string_old/string_new/g'  *.report

Test what character has the specified octal value

e.g. octal = 200

Can be useful when debugging issues with character types.

$ echo $'\200'

References

• Linux command directory
• Bourne Shell Scripting and Quick Reference
• AWK scripting
• SED stream editor
• bash commands