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diff will usually only take one file from STDIN. This is a method to take the result of two streams and compare with diff. The example I use to compare two iTunes libraries but it is generally applicable.
diff is designed to compare two files. You can also compare directories. In this form, bash uses 'process substitution' in place of a file as an input to diff. Each input to diff can be filtered as you choose. I use find and egrep to select the files to compare.

Sum columns from CSV column $COL
More of the same but with more elaborate perl-fu :-)

Wrap text files on the command-line for easy reading
fold wraps text at 80 characters wide, and with the -s flag, only causes wrapping to occur between words rather than through them.

Run a command if file/directory changes
Example: $ runonchange /etc/nginx nginx -t Ignores vim temp files. Depends on 'inotify-tools' for monitoring of file changes. Alternative to tools like 'entr', 'watchr'.

Create a visually twisted effect by alternating the direction of the "staples" effect vertically. The effect is achieved by moving odd-numbered lines from right to left and even-numbered lines from left to right.
The effect is achieved by moving odd-numbered lines from right to left and even-numbered lines from left to right. For odd-numbered lines (with an index j), the ((j + i) % 2 == 0) condition is satisfied. In this case, the line width is set to i, resulting in the line moving from left to right. For even-numbered lines, the ((j + i) % 2 == 0) condition is not satisfied. The line width is set to $(tput cols) - i, causing the line to move from right to left. This alternating direction of movement creates a twisted visual effect as the lines appear to move in opposite directions. The code runs in a continuous loop, repeatedly updating the lines with changing background colors. There is a slight pause of 0.05 seconds between each iteration to control the speed of the animation.

Get AWS temporary credentials ready to export based on a MFA virtual appliance
You might want to secure your AWS operations requiring to use a MFA token. But then to use API or tools, you need to pass credentials generated with a MFA token. This commands asks you for the MFA code and retrieves these credentials using AWS Cli. To print the exports, you can use: `awk '{ print "export AWS_ACCESS_KEY_ID=\"" $1 "\"\n" "export AWS_SECRET_ACCESS_KEY=\"" $2 "\"\n" "export AWS_SESSION_TOKEN=\"" $3 "\"" }'` You must adapt the command line to include: * $MFA_IDis ARN of the virtual MFA or serial number of the physical one * TTL for the credentials

Tricky implementation of two-dimensional array in Bash.
Since Bash doesn't support two-dimensional arrays, you can limit your columns length by some big enough constant value ( in this example 100 ) and then index the array with i and j, or maybe write your own get() and set() methods to index the array properly like I implemented for example ( see Sample output ). For example for i=0 and j=0...99 you'll pick up one of 100 elements in the range [0,99] in the one-dimensional array. For i=1 and j=0...99 you'll pick up one of 100 elements in the range [100,199]. And so on. Be careful when using this, and remember that in fact you are always using one-dimensional array.

Create date based backups
This script creates date based backups of the files. It copies the files to the same place the original ones are but with an additional extension that is the timestamp of the copy on the following format: YearMonthDay-HourMinuteSecond

prettier "cal" command
Displays the same output as "cal", but with the current day highlighted (probably dependent on gnu grep, as I'm not sure other grep's support the "--color=auto" option). Tested and working on Ubuntu 11 and OSX Lion.

Drop all tables from a database, without deleting it


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