Category: Linux

Creating a Samba Share and Configuring an Access Control List for a Shared Directory Under Linux

Posted on by rchapin

Often administrators would like to configure a Samba share that enables users to have the same access to any files within the share.  Without some additional configuration, directories and files created by one user will not have the r/w permissions for other users that have access to that same share.

The end goal is to have a Samba share in which any new files are created with r/w permissions for a specific group to which all of the members of → Continue reading “Creating a Samba Share and Configuring an Access Control List for a Shared Directory Under Linux”

Use awk to Print from nth element to the End of the Line

Posted on by rchapin

If you want to extract from the nth token to the end of the line, following is how you can do that with awk:

Given a source file with the following:

line1 -- 01   0011 1
line2 -- 01   0011 2
line3 -- 01   0011 3
line4 -- 01   0011 4
line5 -- 01   0011 5
line6 -- 01   0011 6
line7 -- 01   0011 7
line8 -- 01   0011 8
line9 -- 01   0011 9
line10 -- 01   0011
→ Continue reading “Use awk to Print from nth element to the End of the Line”

Firewall for Ubuntu 14.04 LTS

Posted on by rchapin

For whatever reason, Ubuntu 14.04 does not seem to come with a firewall.

There are however two packages which provide, both a firewall and a handy GUI front-end for it.  UncomplicatedFireWall is the main package (ufw) and the GUI is gufw.

To install:

apt-get install gufw

This will install the front-end and the dependent packages

To turn it on:

ufw enable

The default is to block all incoming traffic.

To update and add your own firewall rules and allow incoming → Continue reading “Firewall for Ubuntu 14.04 LTS”

Generate a Random String of a Specified Size with a Shell Script

Posted on by rchapin

The following is a one-liner for generating a random string of a fixed size in bash, where the possible characters to use in the string are any digit, letter, and a newline.

By adding the newline, you are fairly sure to prevent getting one long line of text.

< /dev/urandom tr -dc "[:digit:][:alpha:][\n]" | head -c1000 file.out
→ Continue reading “Generate a Random String of a Specified Size with a Shell Script”

One-Liner for Converting CRLF to LF in Text Files

Posted on by rchapin

If you have text files created under DOS/Windows and need to convert the CRLF (carriage return and line feed) characters to LF (line feed) character, here is a quick one-liner.

cat file.txt | perl -ne 's/\x0D\x0A/\x0A/g; print' file.txt.mod

You can also use dos2unix, however, especially under Cygwin I have seen dos2unix fail without giving any meaningful information about why it was unable to complete the task.  In that case, you can just do it by hand. → Continue reading “One-Liner for Converting CRLF to LF in Text Files”

Parsing Command Line Arguments with getopt in Bash

Posted on by rchapin

When writing utility scripts in Bash it is tempting to simply pass positional arguments, use $1, $2, etc. and be done with it.  However if you want to either share this utility with other members of your team and/or incorporate it into your system, it makes sense to implement your command line argument parsing in a more flexible and maintainable manner.

Using getopt you can very easily pass a variety of command line options and arguments.

Following is a link → Continue reading “Parsing Command Line Arguments with getopt in Bash”

Vim Search and Replacing with Backreferences

Posted on by rchapin

It is often helpful to write search and replace commands that save segments of the matched text to use in the replacement string.

Source text:

This is some text (we want to change) with a phone number (301) 555-1234.
We want to remove the parenthesis, but only from the phone number string.

In this example we have a text file that has a phone number in it and we want to remove the parenthesis that surround ONLY the area code → Continue reading “Vim Search and Replacing with Backreferences”

Print Lines in a File From a Specific Line Number Until the End of the File with sed

Posted on by rchapin

If you know that you want all of the lines in a given file from n to EOF the following is the sed command:

sed -n '3,$p' some_file.txt

To print out lines 2 – 5 simply modify it to:

sed -n '2,5p' some_file.txt

→ Continue reading “Print Lines in a File From a Specific Line Number Until the End of the File with sed”

Removing the Last Token From a String in Bash with awk

Posted on by rchapin

Let’s say that you have some number of files for which you want to create a containing directory that is named with all but the last token of the file name, and you want to remove just the last token to create the name of the directory.

Much easier to explain with an example.  Given this list of files:

ls -1
foo_10_10_sometrash
foo_1_sometrash
foo_2_sometrash
foo_3_sometrash
foo_4_sometrash
foo_5_5_sometrash
foo_5_sometrash
foo_6_6_sometrash
foo_7_7_sometrash
foo_8_8_sometrash
foo_9_9_sometrash

You want to create a directory for each → Continue reading “Removing the Last Token From a String in Bash with awk”

Removing The Last N Character From a String in Bash Script with sed

Posted on by rchapin

Here is a quick one-liner for trimming a specific number of characters from the end of a string under bash:

# Remove the last 5 characters
$ echo "somestringwith12345" | sed "s/.....$//g"
$ somestringwith

# Remove the last 3 characters
$ echo "somestringwith12345" | sed "s/...$//g"
$ somestringwith12
→ Continue reading “Removing The Last N Character From a String in Bash Script with sed”
© 2005 Ryan Chapin