Coding School

Problem
You want to get up and running with sqlite

Solution
Install sqlite3 on linux, via yum: yum install sqlite3Then just run sqlite dbname

Example
% sqlite3 testdata.dbSQLite version 3.5.9Enter “.help” for instructionssqlite> create table memos(text,priority INTEGER);sqlite> insert into memos values(’deliver project description’,10);sqlite> insert into memos values(’lunch with Christine’,100);sqlite> select * from memos;deliver project description|10lunch with Christine|100sqlite>

Reference
sqlite3 linux man [...]

Problem
Different versions of UNIX handle the stripping of newlines in a string differently. Obviously if you echo a string, the shell automatically expands newlines “\n”.

Solution
sed and tr don’t appear to like performing these substitutions. But with Perl its a steal.

Example
% echo ‘hello world\nhello world\ntest it’ | perl -ane ’s#\\n# #g; print,”";’hello world hello [...]

Problem
You want to resize images from the command line.

Solution
Use image magik mogrify command.mogrify -resize “percentage” image_naAlso you can view current sizing – like this:% identify IMG_3864.JPGIMG_3864.JPG JPEG 563×422 563×422+0+0 DirectClass 8-bit 32.8887kb

Example
mogrify -resize 20% IMG_3705.JPG

Reference
Technorati Tags: mogrifymogrify man page – resize an image

Link to this post!

Problem
You want to get notified when a file arrives. Maybe it is coming in from somewhere else, or just is the result of some processing.What ever the case, never sit there waiting for a file to arrive again!

Solution
Put the code under example tab, in a cron entry. See reference for more detail [...]

Problem
You want to compare 2 streams, with byte offset and line numbers?Pull off content with a byte offset?Display lines before or after a pattern?Send an email – upon job failure?

Solution
The shell is a powerful beast! Anything is possible … with a little know-how. See the examples.

Example
md5sum TARBALL | awk ‘{print $1;}’ | [...]

Problem
You want to make some backups with tar.

Solution
tar is very functional and has many uses.

Example
If you are lucky enough to have GNU tar (tar –version will return GNU if so), then you can compress and backup at the same time. tar zcvf /tmp/filename.tgz .This backups and zips the contents of the current directory, to [...]

Problem
You want to forward all traffic from a port on your box, to another host/port combination.

Solution
The command in the example will port forward, from the local box – any traffic sent to port 8081, will be sent to port 8080 on www.example.com:

Example
ssh -x -g -L 8081:www.example.com:8080 localhostDon't forget, if you need to open LINUX (FC4) [...]

Problem
You want to display line lengths – then average line length of file.

Solution
Snip using awk – see example.

Example
awk ‘ { thislen=length($0); printf(”%-5s %d\n”, NR, thislen); totlen+=thislen}END { printf(”average: %d\n”, totlen/NR); } ‘ filename

Reference
Technorati Tags: gawk, Unix Coding SchoolLinux Man Pages – gawk command

Link to this post!

Problem
You want to loop around a number of times and perform an action.

Solution
Being able to loop around a given number of times, fully utilizes the power of UNIX. See the example.

Example
For example, spin around 100 times and print hello:i=0; while [[ $i -lt 100 ]] ; do echo -n “hello”; ((i++)) ; done; echo “”hellohellohellohellohellohellohellohellohellohellohellohellohellohellohellohellohellohellohellohellohellohellohellohellohellohellohellohellohellohellohellohellohellohellohellohellohellohello…Similarly [...]

Problem
Ever wanted to produce columns of output, rather than your output spilling off the screen.

Solution
Useful command for this is paste, see example for how it works – to split output into 3 columns.

Example
ls | paste – - -comments.php comments-popup.php fat.jsfooter.php header.php index.phpscreenshot.png sidebar.php style.cssAs you'd expect with UNIX, [...]