Shell

Set default editor

export EDITOR=vim

We can set this variable in the .profile or .bashrc file.

chmod Numerical permissions

A permission have 3 numbers: owner, group and anyone else. An example, 744 stands for; the owner can read, write and execute, group and anyone else can read only the file.

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Append Current Date To Filename in Bash Shell

To get the current date in mm_dd_yyyy format use the following date format syntax:

date +"%m_%d_%Y"

You can store this to a variable name:

now=$(date +"%m_%d_%Y")

or

now=`date +"%m_%d_%Y"`

Finally, you can create a filename as follows:

now=$(date +"%m_%d_%Y")
echo "Filename : /nas/backup_$now.sql"

You can create a shell script as follows:

#!/bin/bash
_now=$(date +"%m_%d_%Y")
_file="/nas/backup_$_now.sql"
echo "Starting backup to $_file..."
# mysqldump -u admin -p'myPasswordHere' myDbNameHere > "$_file"

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How can I delete duplicate lines in a file in Unix?

$ awk '!seen[$0]++' file.txt

seen is an associative-array that Awk will pass every line of the file to. If a line isn’t in the array then seen[$0] will evaluate to false. The ! is a logical NOT operator and will invert the false to true. Awk will print the lines where the expression evaluates to true. The ++ increments seen so that seen[$0] == 1 after the first time a line is found and then seen[$0] == 2, and so on. Awk evaluates everything but 0 and "" (empty string) to true. If a duplicate line is placed in seen then !seen[$0] will evaluate to false and the line will not be written to the output

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How to check spelling at the Linux command line with Aspell

To check the spelling of a file, just type:

$ aspell check file.txt

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How to use unicode characters in Windows command line?

In powershell type:

chcp 65001

It will change the code page to UTF-8. Also, you need to use Lucida console fonts.

(I use this to build a hakyll project on Windows)

Another answer at Windows 10 terminal encoding.

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tar usage

$ tar -czf filename.tar.gz file-1 [file-2 file-3 ...]  # creates a tar.gz o tgz file
$ tar -ztvf filename.tar.gz                            # list the content of a tar.gz or .tgz file
$ tar -xzf filename.tar.gz                             # extract the content of a tar.gz or .tgz file

How do I scroll in tmux?

Ctrl-b then [ then you can use your normal navigation keys to scroll around (eg. Up Arrow or PgDn). Press q to quit scroll mode.

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