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remove comments (even those starting with spaces), empty lines (even those containing spaces) in one grep command
useful for discarding even those comments which start with blanks or those empty lines which contain blanks

Clean apt-get and gpg cache and keys
Cleans apt-get and gpg cache and keys

Debug your makefile
Say your dependencies specified in your Makefile (or dates on your source files) is causing 'make' to skip some source-files (that it should not) or on the other other end, if it is causing make to always build some source-files regardless of dates of target, then above command is handy to find out what 'make' thinks of your date v/s target date-wise or what dependencies are in make's view-point. The egrep part removes the extra noise, that you might want to avoid.

Default value or argument
I used it for this function, which prints hashes: function liner { num_lines=${1:-42} echo printf %${num_lines}s|tr " " "#" echo } Note the colon-dash, instead of the usual colon-equals.

Doing some floating point calculations with rounding (e.g. at the 3rd decimal)

Convert images (jpg, png, ...) into a PDF
Converts images (maybe from scans) into a PDF

Change the console keyboard layout

Find and display most recent files using find and perl
This pipeline will find, sort and display all files based on mtime. This could be done with find | xargs, but the find | xargs pipeline will not produce correct results if the results of find are greater than xargs command line buffer. If the xargs buffer fills, xargs processes the find results in more than one batch which is not compatible with sorting. Note the "-print0" on find and "-0" switch for perl. This is the equivalent of using xargs. Don't you love perl? Note that this pipeline can be easily modified to any data produced by perl's stat operator. eg, you could sort on size, hard links, creation time, etc. Look at stat and just change the '9' to what you want. Changing the '9' to a '7' for example will sort by file size. A '3' sorts by number of links.... Use head and tail at the end of the pipeline to get oldest files or most recent. Use awk or perl -wnla for further processing. Since there is a tab between the two fields, it is very easy to process.

Sort IPV4 ip addresses

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


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