AmirWatad.com » Bash

Bash Tip – Separate a Bash Variable From Surrounding Letters

Amir Watad — Fri, 23 Apr 2010 22:25:05 +0000

Sometimes, you might find yourself needing to concatenate the value of a bash variable with a string.
I think it’s best demonstrated with (a somewhat artificial) example:

1
2
3

y=h
echo $yome #won't work. will print the value of the variable "yome" which is a null string (since it's not set)
echo ${y}ome #works. will print "home"

That’s it, the trick is to use the curly brackets ${var} to separate the variable from its surrounding.

Have fun

source: @bashcookbook

--------- Note: Some RSS readers might display this post with incorrect format. View original post at AmirWatad.com

Bash Tip – Separate a Bash Variable From Surrounding Letters

Re-Use A Bash Command With Different Parameters

Amir Watad — Sun, 27 Sep 2009 13:00:31 +0000

Suppose you have typed and executed this command in your Linux shell:

1	./script_a.sh 1.23 && ./script_b.sh 1.23 && ./script_c.sh 1.23.45

Now you want to run the same command, but with 2.34 instead of 1.23
A nice way to do it is this:

1	!!:gs/1.23/2.34

Meaning, run the last command (!! is also called ‘bang bang’, and it’s substituted by the last command you executed), and replace every instance of 1.23 by 2.34

via Unix Bash Scripting.
Have fun

--------- Note: Some RSS readers might display this post with incorrect format. View original post at AmirWatad.com

Re-Use A Bash Command With Different Parameters

Trimming Bash Variables – A Summary

Amir Watad — Sat, 05 Sep 2009 15:07:03 +0000

This post should summarize the subject of stripping out bash variables, we already talked about on previous posts

Let’s say we have a bash variable (say x), which stores a string (say “ExExampleStringStr”)

Then we can do the following manipulations:

1	y=${x%Str*}

This will trim out the shortest match of the pattern “Str*” from the end of the string.
Thus, y will have the value “ExExampleString”.

2.

1	y=${x%%Str*}

This will trim out the longest match of the pattern “Str*” from the end of the string.
Thus, y will have the value “ExExample”.
3.

1	y=${x#*Ex}

This will trim out the shortest match of the pattern “*Ex” from the beginning of the string.
Thus, y will have the value “ExampleStringStr”.
4.

1	y=${x##*Ex}

This will trim out the longest match of the pattern “*Ex” from the beginning of the string.
Thus, y will have the value “ampleStringStr”. (since ExEx is the longest match of the pattern *Ex)

So remember:
# or ## = beginning
% or %% = end
## or %% = longest match
# or % = shortest match
* is a wildcard matching “any string” (including the empty string).

These tips are according to @bashcookbook‘s. I recommend following him on twitter for many useful bash tips
Have fun

--------- Note: Some RSS readers might display this post with incorrect format. View original post at AmirWatad.com

Trimming Bash Variables – A Summary

Strip Leading Characters Off A String

Amir Watad — Fri, 04 Sep 2009 09:05:49 +0000

Say you have a bash variable (say x) storing the string “MyLongString”

This bash command:

1	echo ${x##My}

Will strip the leading string “My” off the original string. And thus the output will be:

LongString

via @bashcookbook

--------- Note: Some RSS readers might display this post with incorrect format. View original post at AmirWatad.com

Strip Leading Characters Off A String

Strip the File Name Suffix off a Bash Variable

Amir Watad — Tue, 01 Sep 2009 21:18:10 +0000

Suppose you have a bash variable storing a file name, say x =file.jpg

You can use this substitution command in order to strip out the file suffix off the string:

1	echo ${x%.*}

The output will be the base name of the file without the suffix.

via @bashcookbook

Enjoy

--------- Note: Some RSS readers might display this post with incorrect format. View original post at AmirWatad.com

Strip the File Name Suffix off a Bash Variable

Create Multiple Nested Directories in Linux

Amir Watad — Fri, 03 Jul 2009 09:27:20 +0000

Did you know that you can create a complete directory tree with one command?

Let’s start with a simple example:

mkdir -p a/b/c

will create this tree:

`-- a
    `-- b
        `-- c

And any of these:

mkdir -p a/{b1,b2}/c

mkdir -p a/b{1,2}/c

Will create this tree:

`-- a
    |-- b1
    |   `-- c
    `-- b2
        `-- c

And a little more complicated command:

mkdir -p a/b{1,2,3/c{1,2}}/d

Will create this tree:

`-- a
    |-- b1
    |   `-- d
    |-- b2
    |   `-- d
    `-- b3
        |-- c1
        |   `-- d
        `-- c2
            `-- d

--------- Note: Some RSS readers might display this post with incorrect format. View original post at AmirWatad.com

Create Multiple Nested Directories in Linux

Tiny Bash Functions to Convert Between Numeric Representations

Amir Watad — Fri, 12 Jun 2009 15:02:20 +0000

I have these functions in my aliases file. They make it easy to convert between hex, binary and decimal representations of numbers. You might find it useful.

Just add these to your aliases file (imported from ~/.bashrc):

1
2
3
4
5
6

function h2d { echo "obase=10; ibase=16; $( echo "$*" | sed -e 's/0x//g' -e 's/$[a-z]$/\u\1/g' )" | bc; }
function h2b { echo "obase=2; ibase=16; $( echo "$*" | sed -e 's/0x//g' -e 's/$[a-z]$/\u\1/g' )" | bc; }
function b2d { echo "obase=10; ibase=2; "$*"" | bc; }
function b2h { echo "0x$(echo "obase=16; ibase=2;"$*"" | bc)"; }
function d2b { echo "obase=2; ibase=10; "$*"" | bc; }
function d2h { echo "0x$(echo "obase=16; ibase=10; "$*"" | bc)"; }

Now you should be able to use it like this:

h2d 0xff

The output will be 255 in this case.

h2b is for “hex to binary”, the others are similar (h: hex, b: binary, d: decimal)

Enjoy

--------- Note: Some RSS readers might display this post with incorrect format. View original post at AmirWatad.com

Tiny Bash Functions to Convert Between Numeric Representations

Renaming Files In Linux

Amir Watad — Fri, 29 May 2009 22:40:03 +0000

In a previous post, I wrote about converting strings from camelCase to undescore delimited format.

In this post, we’ll do the same but for file names. We’ll use the command line program “rename” for this purpose.
Here we go:

1. Convert all file names in current directory which are of the form “myFileName” or “MyFileName” into the form of “my_file_name”:

1	rename 's/(.)([A-Z])/$1_\l$2/g' * && rename 's/([A-Z])/\l$1/g' *

2. Convert all file names in current directory which are of the form “my_file_name” into the form “myFileName”:

1	rename 's/([a-z])_([a-z])/$1\u$2/g' *

3. Convert all file names in current directory which are of the form “my_file_name” into the form “MyFileName”:

1	rename 's/([a-z])_([a-z])/$1\u$2/g' * && rename 's/^([a-z])/\u$1/g' *

Enjoy

--------- Note: Some RSS readers might display this post with incorrect format. View original post at AmirWatad.com

Renaming Files In Linux

Convert camelCase to Underscores Using sed

Amir Watad — Fri, 29 May 2009 22:15:34 +0000

This short post deals with converting strings of the form camelCase or CamelCase into camel_case, and vice versa. These are three different popular naming conventions for variable/function/class names.

Convert CamelCase or camelCase to camel_case:

1	sed -e 's/$[A-Z]$/_\l\1/g' -e 's/^_$[a-z]$/\1/g' file.txt

Convert camel_case to camelCase

1	sed -e 's/_$[a-z]$/\u\1/g' file.txt

Convert camel_case to CamelCase:

1	sed -e 's/_$[a-z]$/\u\1/g' -e 's/^$[a-z]$/\u\1/g' file.txt

--------- Note: Some RSS readers might display this post with incorrect format. View original post at AmirWatad.com

Convert camelCase to Underscores Using sed

Sed and AWK – A quick reference

Amir Watad — Sat, 09 May 2009 11:45:57 +0000

Sed (Stream Editor) and AWK (First letters of the surnames of its authors) are very powerful *nix tools for manipulating strings and text files. They combine the power of regular expressions with the power of a programming language for this aim.
Here are two quick references for doing many operations with a one-line code of sed and AWK. (Both are by the same author – Eric Perment):

sed 1-line
awk 1-line

I use these very frequently, as they cover almost anything I would want to do with text files. I loved the simple format the author has chosen to use (plain text).

Another great document (also by Eric Perment) is a comparison between sed and awk commands:
AWK vs. sed

Visit Eric’s homepage to find more sources and information about sed, AWK, perl and other stuff.

Enjoy

--------- Note: Some RSS readers might display this post with incorrect format. View original post at AmirWatad.com

Sed and AWK – A quick reference