BASH: print fields from file

If you want to print only some fields from file use "cut" command

e.g.
You want to list accounts on your system you can obtain it from /etc/passwd:

cat /etc/passwd

root:x:0:0:root:/root:/bin/bash
daemon:x:1:1:daemon:/usr/sbin:/bin/sh
bin:x:2:2:bin:/bin:/bin/sh
sys:x:3:3:sys:/dev:/bin/sh
sync:x:4:65534:sync:/bin:/bin/sync


We are interested only in the first field delimited with ":"
so we run:

cat /etc/passwd | cut -d":" -f1

the first cut parameter "-d" tells what field delimiter will be, the second "-f" says which field number should be printed

BASH: bind directories

If you want to bind one directory to another run this command:

mount --bind /source/directory /newly/created/destination/directory

Note: you need to create /newly/created/destination/directory to be able to bind content of /source/directory to it.


To permanently have this binding edit your /etc/fstab and put this line:

/source/directory /newly/created/destination/directory none bind 0 0

Next run this command:

mount -a

BASH: reload fstab

If you made some changes in /etc/fstab and want to reload it so they will become visible just run with root privelages:

mount -a

BASH: count files in directory and subdirectories

There is a simple way to count number of files and subdirectories

find /path/to/my/dir -type f | wc -l

BASH and sed: revert file content

If you want to revert file content you can use sed:

cat myFile.txt | sed -n -e '1!G' -e 'h' -e '$p'


Explanation:

sed -n
surpress printing lines

-e '1!G'
append to the pattern bufor content of the temporary bufor (applies to all lines except the first one(

-e 'h'
overwrite temporary bufor with current pattern content

-e '$p'
end of file found - print pattern bufor

sed: replace string with another one in files

Here is the script to replace string in files to another one

phrase_in=$1
phrase_out=$2
if [ ! "$#" -eq "2" ]; then
echo "incorrect number of arguments"
exit
fi
echo $phrase_in
echo $phrase_out
for filename in `grep -r -l $phrase_in .`
do
sed -i "s:$phrase_in:$phrase_out:g" $filename
echo sed -i s:$phrase_in:$phrase_out:g $filename
done

You execute it with two parameters: string_to_search and string_to_replace

Of course there are also other solutions for this problem.
http://www.jonasblog.com/2006/05/search-and-replace-in-all-files-within-a-directory-recursively.html

But this script is mine :)

Git: check what files you changed before pushing

To make sure what files you have changed before pushing them on remote repo run

git diff HEAD origin/master

If you are pushing to branch replace "master" with remote branch name