Bash
Bash Tip – Separate a Bash Variable From Surrounding Letters
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 ${var} to separate the variable from its surrounding.
Have fun 
source: @bashcookbook
Re-Use A Bash Command With Different Parameters
Suppose you have typed and executed this command in your Linux shell:
1 | ./script_a.sh 1.23 && ./script_b.sh 1.23 && ./script_c.sh 1.23.45 |
Now you want to run the same command, but with 2.34 instead of 1.23
A nice way to do it is this:
1 | !!:gs/1.23/2.34 |
Meaning, run the last command (!! is also called ‘bang bang’, and it’s substituted by the last command you executed), and replace every instance of 1.23 by 2.34
via Unix Bash Scripting.
Have fun
Trimming Bash Variables – A Summary
This post should summarize the subject of stripping out bash variables, we already talked about on previous posts
Let’s say we have a bash variable (say x), which stores a string (say “ExExampleStringStr”)
Then we can do the following manipulations:
1.
1 | y=${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”.
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Strip Leading Characters Off A String
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
Strip the File Name Suffix off a Bash Variable
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
Create Multiple Nested Directories in Linux
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
or
mkdir -p a/b{1,2}/c
Will create this tree:
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Tiny Bash Functions to Convert Between Numeric Representations
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
Renaming Files In Linux
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
Convert camelCase to Underscores Using sed
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 |
Sed and AWK – A quick reference
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):
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About Me
My name is Amir Watad. I have a BSc. in biomedical engineering from The Biomedical Engineering school , Technion , Israel, and a BSc. in electrical engineering from The Electrical Engineering school , Technion , Israel.
I'm a Verification Engineer in Mellanox Technologies Ltd.
I love Linux, the Command Line and the OpenSource Community.
I used to write Poems (Arabic) when I was able to find time for this.
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