Category: Software

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”

Passing an Array as an Argument to a Bash Function

Posted on by rchapin

If you want to pass an array of items to a bash function, the simple answer is that you need to pass the expanded values.  That means that you can pass the data as a quoted value, assuming that the elements are whitespace delimited, or you can pass it as a string and then split it using an updated IFS (Internal Field Separator) inside the function.

Following is an example of taking the output of a Hive query (a single → Continue reading “Passing an Array as an Argument to a Bash Function”

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”

Checking that Input or a Variable is an Integer in BASH

Posted on by rchapin

Here is a quick snippet for checking whether or not a variable is a valid integer in BASH.  It is also a howto for regular expressions in a shell script.

# Make sure that FOO is an integer
if [[ ! "$FOO" =~ ^[0-9]+$ ]]; then
        echo "The FOO was NOT an integer"
fi
→ Continue reading “Checking that Input or a Variable is an Integer in BASH”

Creating an Array in Bash from a File With Each Element on a Separate Line

Posted on by rchapin

Let’s say that you have a file and you would like to convert each line in the file to an element in an array.

The key to this is knowing about and how to manipulate the IFS (Internal Field Separator).  The default IFS is whitespace (a space, tab, or newline) and if you create an array passing it a whitespace delimited list of strings, each token will be set to an element in the array.

ARRAY=(a b d
→ Continue reading “Creating an Array in Bash from a File With Each Element on a Separate Line”

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”

Running Multiple Instances of Notepad++ Under Windows 7

Posted on by rchapin

If you want to run multiple versions of Notepad++ under Windows 7 create a .bat file with the following:

"C:\Program Files (x86)\Notepad++\notepad++.exe" -multiInst %1

And simply run the bat file via a cmd prompt/ → Continue reading “Running Multiple Instances of Notepad++ Under Windows 7”

© 2005 Ryan Chapin