Extract only the number from a file name

Some times you may want to extract only the number from a file name, especially when you are working with a huge number of files to do some calculation or to run jobs.

This can be done by (for foo_bar_xyz_file_01_input.in)

echo $f|cut -d_ -f5

Here, $f is the file name.
-d is the delimeter
-f5 is the field where the number is present.

sed tutorial

The stream line editor 'sed' and the 'AWK' are the simple and highly useful languages for processing text files.

Here are some of the tips and tricks to use "sed". Later, I will post on AWK usage.

sed -n '/matchingWord/p' foo.txt

[Note that this is similar to: grep "matchingWord" foo.txt which seems to be very simple for this task. But for many instances, 'sed' may do more.]

sed -i -e 's/match/replacingText/g' hello.txt

Here, the line containing 'match' will be replaced with 'replacingText.




-e : just displays the outcome but don't change the file

-i : change the file (writes in the file)

s  : substitute

g  : is for global substitution. If need only first match, remove g.

Last one is the file name.

You can use this to a bunch of files. 

sed -i -e 's/match/replacingText/g' file*.txt

To delete lines with match pattern

sed -i '/pattern/d' FileName

To replace ":" with " " 

The sed expression s/:/ /g replaces every ":" with a "space".
That is sed substitutes an empty space for every ":" character globally in the file


Sometimes, there may be a need to remove (which is better than replacing a line which contain special characters)

To remove use following onliner

sed '/pattern to match/d' ./filename

To modify the file itself

sed -i '/pattern to match/d' ./filename

Replace the second line (or nth line, first line, third line, etc) using sed:

sed -i '2s/.*/0 5/' c*.in

For other posts like this, see
AWK


For more see following links:
https://stackoverflow.com/a/5410784/6628192