How to verify sha256sum for multiple file or one file.

So, lets say you have downloaded the SHA256SUMS files. This file contains the sha256sum for multiple files and you want to compare the values for only one or some of them, then the simplest thing you can do is:

sha256sum -c SHA256SUMS

Now, with this if you do not have some files present then you might get some errors and if you do not want that, then you can try this:

Get count of lines in scripts (shell)

If you have tried to get the count of lines in file, the you would know about “nl” or “wc -l”. But as you are aware these give you number of lines with other details as well and you need to post process the number to make sure that you have only number and nothing else. In such cases, it is useful to use the count feature of grep and here is a shorthand to get the count of lines in any shell script:

bash – expand shell variables ( bash bug resolved )

As you would have noticed in the recent versions of bash, expansion does not work properly when expanding directory names. So, for something like this

cd $varname

if you press tab, then variable name does not expand properly.

If this is something that is bothering you then you can now add the following in your bashrc and revert to older behaviour:

shopt -s direxpand

Hope this helps you.

ShellCheck – check basic POSIX shell script errors

Here is description of the tool:

Description : The goals of ShellCheck are:

• To point out and clarify typical beginner’s syntax issues,
  :   that causes a shell to give cryptic error messages.

• To point out and clarify typical intermediate level semantic
  :   problems, that causes a shell to behave strangely and
  :   counter-intuitively.

• To point out subtle caveats, corner cases and pitfalls, that may
  :   cause an advanced user’s otherwise working script to fail under
  :   future circumstances.

To install

nice little bash function to search for running processes

Here is a nice little handy function that I use very regurlarly.

You can use this function with parameter to just grep for that or just type psa to see all the running processes.

Just put this in your .bashrc file.

You might find it useful:

psa () 
{ 
    if [[ $1 == "" ]]; then
        ps -eaf;
    else
        ps -eaf | grep --color=auto -i $1;
    fi
}

bash – refer the first parameter from last command quickly

To refer to first parameter from the last command quickly, you can use

!^

Note: This can also be referred as “!!:1“

bash refer parameters from the current command

In bash you can use

!#

to refer to any parameter from the current command, example:

mv ak amit.!#:1.txt
ls amit.ak.txt